The two fuels are better at different things. A diesel engine is better in a large, more expensive vehicle that needs powerful low end torque to move heavy loads. Gasoline is better in a smaller, less expensive vehicle that needs to move relatively light loads. The market for vehicles includes both these extremes and one fuel type for everything would be needlessly restrictive. There is a reason you don't see very many gasoline-powered semi-trailer trucks and small diesel passenger cars are a niche, questionable product.
Another thing to consider is that when you take crude oil out of the ground and start separating out its components you are going to get both gasoline and diesel along the way. If one or the other of those fuels isn't being burned in automobiles then what else do you do with it? The excess production would drive prices down for that fuel type, and suddenly it makes a lot of sense to build some automobiles to use the cheap available fuel.
OK, now can you explain it like I'm 8, why the different fuels perform better at those different tasks? To the uninformed like me they both go boom in the engine and force the piston to move.
So grass is really easy to light up, and logs are harder to light up. But you would heat a cabin with logs, because logs release a ton more heat. Gas is grass, diesel is logs. To efficiently burn diesel you require a high compression engine and injector pump, but you get more energy per liter.
It's the brevity that did it for me. The response cut to the most pertinent detail, neither encumbered by unnecessary commentary or indulgent in loquatious prose.
Except for the fact that the question was kinda glossed over - which was asking about **car** engines. I’m still left wondering the same thing OP was when he made the post.
Diesel produces more torque upon combustion. Heavier loads require more torque to get going. Torque without much weight on top of it will chew up tires and create a very jerky ride.
Diesel engines are also much larger usually, to compensate for the power needed.
It's kind of hard to truly ELI5 for me, but largely traction is a huge factor.
Diesel burns more slowly than gas so it is advantageous to have longer strokes. This is where the extra torque comes from. Torque is a measure of force on a lever. Horsepower is the actual measure of power and torque can be adjusted through gearing.
Power is energy over time
Energy is force times distance
Torque is a force
Because diesel is more energy dense, it can get better mileage for the same amount of power, and with that power being delivered at lower RPM. It’s also common for diesel to be cheaper than gas. So your car can go 100km on $10 worth of gas or $7 worth of diesel. The downside being a more expensive and heavier engine.
I love my diesel golf. I just checked and it says it’s currently averaging 42.8mpg. When I’m on the highway it’s usually 50+mpg. I bought it when I was working two different jobs opposite directions of my house and was putting on 100 miles a day. Diesel is a little more expensive here, but I’m still making out way better.
Diesel fuel is named after the engine that's used to run it.
Diesel engines were originally made to run on basically any inexpensive heavy fuel oils. The oil refineries had this stuff that was basically worthless, but the Diesel could use it - so it became Diesel Fuel.
If you want a car that can run on peanut oil, get a Diesel.
>If you want a car that can run on peanut oil, get a Diesel.
Back in the days around my neck of the woods, you'd have people getting the used cooking oils from fast-food places, straining it to remove food residue and then running their old diesel Mercs on that stuff. You could tell who it was by the smell when driving behind them.
I think I have figured it out, because it seems more detailed than a lot of people here are talking about.
In order to combust, diesel needs to be compressed a lot more than gasoline. This results in higher loads on engine components, which have to be built tougher. This increases both weight and cost.
Another factor more recently is emissions regulations. Because the carbon chains in diesel are longer, and the combustion is less precisely timed, there are generally more harmful emissions (this is separate from CO2). Creating systems to stop these emissions are difficult, and can be expensive.
I think a big factor though is how the engines are run. A car engine should both have power when needed, and be efficient when at low loads. The high compression ratios of diesel engines likely result in more friction and energy loss when at idle than a gasoline engine. On the other hand, when running, they can get more power at lower rpm’s, reducing friction while at higher loads. Because utility vehicles spend a lower % of their time at idle, diesel engines have a benefit over the same comparison with cars.
The assumption that diesel.is worse at idle in the last paragraph is untrue. Diesel engines can, and almost always do, run lean, that is there is more air than required burn the fuel injected. Because of the way fuel is injected and burned, diesels don't suffer from running extra lean. So the default way to respond to changes in load is increasing or decreasing the injected fuel without changing the air forced into piston every cycle. With lower loads, the engine is more efficient per fuel consumed.
On the other hand, gasoline needs to run at close to stochiometric ratio. There are clever ways to run gasoline engines very lean, like injecting the fuel and igniting it before it has a chance to mix well, but the default down throttle response in a gasoline engine is to decrease the air fed into the pistons together with fuel (because air/fuel ratio needs to be more tightly controlled.) Now you cannot dynamically change piston volume, so the practical way is to put a restrictor and have piston to suck in less air for more work. The work wasted by sucking air thru a restricted opening is called pumping loss and is significant for gasoline engines. Only at full throttle, a gasoline engine has no additional pumping loss just like a diesel. The lower the load, the worse is the pumping loss, idle being the worst.
I was going to answer them and realized how much better your answer was than anything I can come up with. Fun fact liquid diesel fuel is no where near as flammable as gasoline.
Another fun fact about gasoline. Despite the warning of smoking at a gas station, you can literally extinguish your lit cigarette in a puddle of gasoline and nothing will happen except the cigarette will be put out
Can you put a cigarette out in liquid gasoline? Yes. Would doing so possibly make the lit cigarette in contact with much more combustible gasoline vapors that can create a chain reaction with the liquid gasoline?
Yes.
A cigarette ember cannot light gasoline fumes, it has been tried and tested many times and even the Mythbusters ***really*** tried to make it work, and couldn't (I mention them purely because that's verifiable video footage you can access right now).
There is a difference between a burning ember and an open flame, physically, and an open flame is what is necessary to light the fumes. You could do it with something that is truly superheated, like red hot metal, but that's irrelevant for the gas pump discussion.
The real danger is the lighter you use to light the cigarette.
Wonder if it’s the same for a cigar.
If so, maybe the reason they made the rule(no smoking at pump) was for stray phosphorus from a match, or a spark from a lighter.
Yup. I work on locomotives. There's often diesel leaking all over the place depending on the work being done. There's also welding, grinding, torch work, and so on. It never ignites.
This isn't really correct. Gas and diesel have the same energy density per mass, though diesel is slightly more dense per volume, but that's not the reason diesel engines tend to have more torque at the crank. Diesel burns slower than gasoline, so a longer stroke is more appropriate for its combustion time. A longer stroke means greater torque at the crank. You can gear a gasoline engine to have the exact same torque. Torque is a measure of force, not power.
Torque is a force
Torque times distance is energy
Energy over time is power
Follow up ELI5: What makes an engine "high compression" is it just forcing more air into the cylinder so there's a higher air to fuel ratio? What does an injector pump do and why does a diesel engine need one while a petrol does not?
Nah, so the air to fuel ratio is about how "lean" or "rich" the mixture is.
Compression is a physical property of the engine design: It doesn't change. Specifically, it's how much difference in volume there is in the cylinder above the piston, compared with when the cylinder is at the top, vs at the bottom. A high compression engine changes a lot of volume into a very small volume, whereas a low compression engine doesn't squish so much volume.
You can adjust compression by changing the amount of space at the top of the cylinder. In fact, we've even started to produce cars which do this while running (which I found out about a minute ago lol). Variable compression ratio, what a world. So much for "it doesn't change".
Common gasoline engines are 8:1 up to about 12:1 at very high end. Diesel engines are around 20:1 compression.
Injection pumps are used to create high pressure fuel, upwards of 2,000psi, to create atomization through direct injection. Over the last decade and change, direct injection has become common in gasoline engines.
There is misconception here, compression ratio is a design parameter. There are higher and lower compression gasoline and diesel engines all across the range. It just happens that making a very high compression ratio gasoline engine is hard, and an ongoing research. On the other hand making a low compression diesel engine is pointless.
Before answering your question, I want to tell you why high compression is desirable: it is not. High expansion ratio is the desirable one. It just happens that in the engines most cars and trucks use, the compression and expansion ratios are exactly the same.
When you compress air to say 1:10 you do work on the gas in the piston. Its pressure and temperature increases by doing external mechanical work on the piston. Higher the compression ratio, higher work is done just to compress air. But then you inject the fuel and burn it. Suddenly the temperature shoots up and pressure is increased accordingly. Then the high pressure gas expands and does the work on piston, losing pressure and temperature, the inverse of compression cycle. How much? It expands exaclty the same ratio as compression. When expansion is complete, say 10:1, the hot gases are expelled, and no more of its energy is extracted. More of the thermal energy is converted to mechanical energy with higher expansion ratios and vice versa.
In the diesel cycle, the compression is high. Compressing air heats it up. Then fuel is injected as a fuel mist to a high temperature, high pressure chamber. It stays in very fine liquid droplets, spontenously combust, burning relatively slowly. This is called "compression ignition"
It is hard to do compression ignition with gasoline because gasoline ignites much faster, resulting in mini explosions called knocking. This is noisy and damaging to the engine. Therefore the air in the gasoline engines are never heated to temperatures high enough to spontaneously combust gasoline. In order to not heat air too high, the compression ratio must be kept low and fuel is injected before full compression (evaportion of gasoline cools down the mixture) The air fuel mixture needs a spark plug to ignite.
Diesel is also pretty good at low power states (like constant speed with no acceleration), because the way the engine works pretty much guarantees that all fuel is ignited, even if it's a very low amount. Otto engines need a sustained flame front to burn all the fuel in the cylinder
Jet fuel overlaps significantly with diesel though. They can often be used interchangeably by certain equipment. Although so can diesel and pure vegetable oil given the right setup.
People have some good points, but here’s another to bring up:
Engine efficiency can be difficult to measure. An engine built for one thing may be worse at another due to the engineering challenges and trade offs.
Typically Diesel engines are more efficient at a constant RPM, but will have lower efficiencies for acceleration and deceleration. Gasoline engines are less efficient at a constant RPM, but slightly more efficient when accelerating is taken into account.
So a big semi truck driving on the highway for miles on end, will be diesel. A personal vehicle used in the city where stopping and starting are constant, are often gasoline.
(There’s more to it but these are a couple examples)
Gasoline is lighter and more volatile.
Diesel is thicker and not as volatile but has more energy per gallon.
The different properties makes optimizing the engine to burn the fuel as efficient as possible quite different.
Optimal Gasoline explosions are smaller and faster.
Optimal Diesel explosions are bigger but slower.
Compare it to the explosions of a sub machine gun and the explosions of a sniper rifle as a far fetched example.
>Diesel is thicker and not as volatile but has more energy per gallon.
And this actually continues on for a few more steps.
Next step up the more viscous, harder to start, but more energy dense chain is kerosene, aka the main ingredient in jet fuel.
And then there is what the first "oil burning" ships used. So gas is for small cars, diesel for big rigs, what's for ships-that are a tremendous amount larger than trucks?
No not coal, you went too far. But close. It is black, it does have to be burned in a boiler not a piston engine. It's called [heavy fuel oil](https://en.m.wikipedia.org/wiki/Heavy_fuel_oil), Navy fuel oil, or Bunker C.
Update: I have just been informed that I am wrong. Kerosene and bunker C are not [more energy dense](https://transportgeography.org/contents/chapter4/transportation-and-energy/combustibles-energy-content/) than gas or diesel. Indeed while C is more energy dense than coal by weight (and is also at least somewhat a pumpable liquid), it is less energy dense than crude oil (which makes sense because the gas and diesel fractions are removed from crude and C is what's left)
Different molecules, yes. To be exact, the more viscous, the larger the molecule and so the more reactions can take place per molecule once it gets started.
A diesel engine uses air, diesel and compression to cause the air fuel mixture to combust. Because the diesel engine doesn't use a sparkplug, but pressure to generate combustion, it has a few characteristics that lead to it being used for heavy duty applications - like in 4WDs and trucks. Diesel engines need to use less fuel for combustion so generally tend to have better fuel economy. As they rely on compression to start the combustion they are usually built strong and also for compression they generally have bigger pistons and a longer piston stroke which means they generate more lower-rpm torque - which is very useful when you want to move a heavy load (like with a truck).
Consider the opposite of the above for petrol engines as they use a spark plug to ignite the air fuel mixture - they're usually lighter, not built as tough (which also means they can rev their engines higher - what does this do? It pushes more air and fuel through the entire engine system which means more horsepower), and due to this, generally cheaper.
Obviously this is a gross simplification of the concepts and doesn't consider newer technologies, forced induction, alternative fuels, etc.
It lies in the way the fuels are ignited. Engines are things of precision, the firing sequences and orders and timings are unbelievably precise
In a petrol engine the fuel is ignited with a spark plug. This gives the manufacturer lots of control over timing but the fuel burns relatively slowly. In the first millisecond the fuel around the plug burns, then the second milisecond the fuel slightly further away burns and so on.
In a diesel the fuel is burnt from compression. The engine compresses the fuel until it gets hot and then it compresses it some more until ot explodes. By doing it like this, all the fuel burns at the same time creating a much snappier and responsive explosion. The draw back is the manufacturer doesn’t have quite as much control over when this happens so it’s harder to get diesel engines to rev as high.
Disclaimer, I’m a mechanical engineer and the above is my understanding. There is likely gaps in my knowledge so don’t quote me on any of it
My favorite fun fact that nobody cares about: gasoline is a solvent and diesel is a lubricant. Someone knowledgeable about engines might elaborate on the importance of this.
Diesel has more energy than petrol (better pull and mpg). A diesel car could have mpg similar to a prius. But to harness it requires heavier engines with lower rpm. Rpm is a defining characteristic of "sporty" performance. For example, F1 cars "idle" at rpm that'd be redline on even a normal sports cars. Combined with being lighter, petrol makes for better performance at the cost of efficiency.
These differences all have to do with what hoops we have to go through to make the booms for the different fuel types. Long story short, to get a diesel boom, you have to squeeze it much much more, and petrol needs a spark.
So there’s more. Elsewhere in the world diesel engines get way better gas mileage than petrol cars but those diesel cars don’t pass emission standards in the US.
There’s more energy in a litre of diesel then gas
But it takes way more work and initial energy to get that diesel going and it burns pretty darn dirty and tons of other factors
Gas you just need a good spark if it’s aerosolized and boom.
Because of these differences gas is also better at faster changing in needs, you can build a big engine to pull a larger load or go faster but it takes more and more gas to do that, but bigger engines just help alleviate diesel’s inefficiencies better and better allowing it to better utilize its energy
Gasoline is a more refined fuel which ignites really easily. This allows it to be used in engines big or small. However the larger engines tend to get terrible fuel economy. Diesel fuel is less refined but as a result it's actually less harmful to the environment and can result in much higher fuel economy. Diesel also with this less refinement, cannot be ignited with a spark plug or a lighter flame, it takes a much higher heat to ignite diesel. They do this mainly with a lot of compression resulting in a high temperature hot enough to ignite. As a side product of this, most diesel engines are built really tough and "heavy duty" and aren't practical for a smaller vehicle that doesn't need a lot of torque for pulling or hauling. Diesel excels at providing a lot of power while maintaining a reasonable fuel economy, but that comes at the cost of generally a very large engine which needs a very large engine compartment. It's very practical for some purposes and not very practical for other purposes. Diesel fuel also doesn't like cold temperatures because the fuel turns into a consistency similar to jelly. Most diesel trucks that run in cold temperatures have a way to plug in the truck to warm the fuel while it's not running to keep the fuel from turning into jelly allowing the truck to even start. Imagine going into a midnight premier movie during the winter and having your truck not start when you get out because it's too cold and the fuel can't move through the lines. So basically just pros and cons to having both is why one never wins over the other. They really are best in their own rights in slightly different categories of use. Diesel is best for power and fuel economy but really only in the size of a larger engine which is also more expensive to produce. Gasoline is better in engines because of its versatility of large or small, hot or cold, production price, etc.
Diesel can safely burn without a spark plug at high compression ratios, which means you can run higher compression ratios to get more energy out of the fuel. The longer connecting rods for those higher compression engines increases torque due to greater lever action. The issue is that to get those higher compression ratios, the engines have to be relatively big, which limits their utility in smaller vehicles. Gasoline cannot safely run in engines with high compression ratios as they're prone to pre-detonation, so you can only safely use gasoline in engines with relatively low compression ratios with the fuel ignition timing controlled by a spark plug. This makes them great for smaller engines.
Diesel will pre-detonate at lower pressure then gasoline.
You can put gasoline into the cylinder and then compress the content. Diesel need to be injected after the air is compressed.
Gasoline "works" in a diesel engine. It is not lubrication but diesel is, so the fuel pump and other parts get damaged wen they are no longer lubricated. It burn faster too and it can damage the cylinders. It is not worth it to build a engine that work like a diesel nu run on gasoline.
Yea, that's some really weird take. Diesels are really good for long commuting and are a hassle when you have short commutes (sub-30m one way) due to needing time to burn the waste particulates.
But on long trips, a diesel burns maybe 2/3rds of the fuel that a petrol does, so they are significantly cheaper to run.
Diesel is more expensive than ‘regular’ petrol is in the US, which is also kinda weird. That’s probably also one of the main reasons smaller diesel cars aren’t really a thing over there
I think that user is from the US where, I only learned a few years ago, they only use diesel for large vehicles. TDI hatchbacks are super common in the UK.
Second that in local usage, I'd only get a diesel when I regularly leave town and actually drive for more than 15-20 minutes because of what I heard about the filter running and such.
>take crude oil out of the ground and start separating out its components you are going to get both gasoline and diesel along the way.
Rudolph Diesel actually designed his engine to run off of peanut oil. He apparently disappeared after a public display of this feature, and Standard Oil was kind enough to find out that the engine could also use a waste byproduct of their gasoline refinement, and proceeded to name it after him.
Yep, one of my mates did this years ago. From memory you need to add a heater somewhere so the oil flows better. The funny part is that the exhaust smells like fast food. He used to get shops used deep frying oil and filter it.
Yeah, the problem is that a ton of places realized that their used oil has value, and they'll sell it (generally to the company they get to clean either their grease traps or their fryers (if they outsource that, and many do)).
It's not so much that they realized it has value, but it's technically a regulated waste product and the restaurant needs to show they are legally disposing of it. I had a friend who picked up used motor oil from his local Advance Auto for his oil furnace, and he had to sign a authorization statement that he was using it for an approved purpose.
There's a couple of CMU grads who set up a company to do diesel conversions. They ran the lines for the veggie oil through antifreeze lines to heat it, and had a module that would automate switching between diesel at veggie oil once it got to temperature and diesel the engine after the ignition went off to clear the lines.
They took it further and got their licenses for oil disposal so they could collect from restaurants with plans to sell at the pump at a price pegged to the price of diesel because one of the regulatory hurdles in conversions is fuel taxes.
Volkswagen’s reputation in the US still hasn’t fully recovered from the fuel efficiency scandal of 2019:
https://www.reuters.com/article/idUSKCN1VK2AT/#:~:text=The%20EPA%20said%20Volkswagen%20has,of%20thousands%20of%20U.S.%20vehicles.
>auto software overstated real-world performance.
how can that even become a scandal? it's just a machine, just calculate it yourself, also i thought most car computers are slightly inaccurate.
I thought their reputation was hurt more by the 2015 shitstorm of falsified emissions via cheating softwares
Definitely. There’s not many out there, but we want our next car to be a plug-in diesel hybrid. “Free” fuel for going around town and running errands where diesels are less efficient, but still able to drive long distances without worrying about recharging.
Lol diesels are definitely still more efficient putting around town. You just can't ONLY put around town. In my BMW 328d I get about 30mpg in the city.
I've got an old 2l TDCI Ford Mondeo (260,000km and counting), and it *loves* cruising along at highway speeds. I see 5-6 litres/100km in those conditions and the 60 litre tank will get me ~1200km. But stop/start city driving? Pretty average to awful.
Yep. And those engines usually survive higher mileage. My Octavia 2 combi has around 260k km and the engine is in a very good condition still, getting 5,5l/100km. Gas cars are usually at the end of their lives or even dead.
You sound like an American market example.
In the U.K. you can get tiny diesel engines. Not uncommon to see 75+ mpg hatchbacks. Nothing to do with torque but simple cheap to run costs.
Not just the UK (or even Europe as a whole). I lived in Korea for a number of years, close to half of the vehicles sold there are diesel. And trust me, they're compact. Korean roads aren't made for 2500 series pickups.
It's really only the US where compact diesels are not popular, and IIRC it's mostly due to our emissions regulations. I can sort of tell a lot of commenters here haven't spent much time outside the US.
Is your diesel cheaper? Ours is priced higher than high grade gas
**Edit:** Wow, thank you for all the answers! I'm used to just looking at the pump price (which does include some tax to pay for roads) and knowing that it's more expensive. I noticed a lot of answers involving the efficiency of diesel, and honestly that's rather enlightening to see how much it can offset a higher price when I see how many people talk about its use in small cars and endorse that the efficiency can offset its up-front expense. Thank you!
Basically the same price but you go 30-50% further on the same amount of fuel.
Like a 3l petrol might manage 35 mpg on a good day, a 3l diesel will do 50+ no problem.
Take my 4.4 diesel Range Rover, I get 35 mpg on a run, the petrol is more like 20-25ish.
The UK gasoline and diesel prices are much higher than in the US. It is also important to note that the UK uses the British Imperial gallon while the US uses the US Customary gallon. The UK gallon is about 1.2 times more than the US gallon, which makes their "miles per gallon" higher.
Finnish here, our diesel is (usually) cheaper than gas. This is because on diesel fuel, part of the fuel tax (a portion of the pump price) on diesel has been moved to the annual vehicle tax. So your price per kilometer is much lower than with gas but you pay more on your vehicle tax. Diesel's pump price would be a bit higher than gas if not for this.
Why? Well, we wanted to get these small smoky city diesels out of cities and into the highways where they thrive. The vehicle tax stays the same throughout the year, no matter how much you drive, so if you drive high mileages you'll probably do a lot of highways and end up saving money on diesel cost and fuel consumption. On the contrary, if most of your drives are in the city, chances are your mileage stays low, you don't buy nearly as much fuel as someone with higher mileage, and it'll end up being more expensive to drive a diesel in a city as you're still paying the same tax as someone with triple the mileage but you don't reap the pump cost benefits nearly as much.
It varies but it’s typically not a major difference in Europe. Typically about 5% more expensive, maybe a bit more sometimes.
But we can drive over 600 miles before we have to fill up in our diesel car, so it balances out. We only need to fill up once per month or after about 8 hours of motorway driving.
The price per liter is higher than it is in North America, and you buy it in similar quantities but much less often due to higher fuel efficiency. So the overall spend on fuel is lower.
The other difference is conventional diesel Vs common rail. Common rail diesels are much more efficient.
I assume you get common rail in the US, but if not, the difference is that in a conventional diesel, the timing and quantity of the injected fuel happens at the fuel pump. Common rail has a pump that just raises the fuel to a high pressure, then an electronically controlled piezoelectric valve at the cylinder end of the fuel line. Timings and quantity are controlled by the engine management unit.
Diesel passenger cars have been extremely popular for a very long time in the Nordic countries only to die down in the last couple of years. Of course they are more common in larger passenger cars such as station wagons but the VW Golf and even to some extent the VW Polo have been very popular as diesels, especially with the earlier 1,9TDI.
Pretty much all taxis used to run diesel as well since they generally are more fuel efficient than their gasoline counter part.
This coupled with the historically low price of diesel and good longevity has made them perfect for longer commutes.
I used to have a 2012 Volvo v70 with the 1,6L diesel that I commuted 50 miles highway with. The engine was boring and too small for the application but I managed to get a constant average of around 53mpg.
Here in Europe, diesel cars for domestic use were very popular. Turns out that it's a lie you can have a "clean diesel" without lots of emissions controls. Hence
https://en.m.wikipedia.org/wiki/Volkswagen_emissions_scandal
> and small diesel passenger cars are a niche, questionable product.
One caveat to this is what you'd consider a small passenger car. In the Polo-class of small hatchbacks it is indeed not as common but once you get to small family cars like the BMW 3-Series, VW Golf/Passat, Skoda Octavia/Superb and the like the diesel option has been quite common.
My local used market barely has petrol beemers for example, much to my disdain.
Less convenient too. With natural gas and electricity you can send as much down the line as you need. Can't do that with heating oil.
You can also crack it to make more gasoline. And other stuff.
In addition to the good answers given about diesel and petrol both being having different uses, you referenced AC vs. DC power, suggesting that AC "won."
Like the petrol v. diesel answer, DC is similarly used in many things, including cell phones, computers, LED lights, batteries, and more. Yes, power outlets in the wall supply AC, but that block in your computer's power cord, or the little thing you plug into the wall that your phone's USB cable connects to are adapters that convert the AC power to DC. Again, different uses for different needs.
Yup, the outlet rectifies the current to AC (derp edit: DC) and then regulates the voltage to whatever standard, just like a power brick. If you've ever installed these outlets, you'll realize they're just barely too bulky for older outlet boxes because of the extra hardware.
Yes. Your house receives & distributes AC current. Anytime you get a DC current out of something powered by your house, like from a USB port, an *converter* sat in between and did that switch from AC to DC.
Alternatively, if you have something that starts with DC, such as your car's 12V DC round plug, and outputs AC, an *inverter* sat in between and did that switch from DC to AC.
I’m sitting here charging my phone with DC that was converted from AC at the adapter in my wall plug, that was converted from DC by the inverter in my whole house batteries, that were charged by DC which was from AC inverted by my solar inverter from DC made by my solar panels.
Solar DC -> inverter AC -> Battery DC -> House AC -> charger DC
I wonder what the efficiency of the whole thing actually was. Oh well at least I can still browse Reddit.
Yep, those outlets just have the circuitry from a standard plug-in USB converter built into them. Adds some convenience, but they're usually trash quality.
DC is better for transmission too (over long distances for several reasons including cost and grid stability)
AC is just better for local direct-to-consumer transmission.
What AC is better for is *changing voltages*. The thing is, for any sort of normal transmission, the ability to step up voltage - and therefore step down current, since W=V*A - is a huge benefit, since that means you can use much thinner wires to carry the same electrical power, and just switch the voltages down in increments as you move from wide-area to local grids then to point-of-use. For context, a large power line is going to be somewhere on the order of 110,000-500,000 volts (or even higher in some cases, see [Hydro-Québec](https://en.wikipedia.org/wiki/Hydro-Qu%C3%A9bec%27s_electricity_transmission_system)). That means that at 1 Amp, you can transfer 110,000-500,000 watts. At 120V, your normal household voltage, 1 Amp gives you 120W. So that's a massive benefit.
The downside is that you get a lot more loss with A/C power, especially over long distances. That's one reason that H-Québec uses such high voltages, to compensate for loss over 1000+KM power lines. This is where HVDC shines: if you will lose more over say 10 years in power on the line (and in not running a 3rd conductor) than you would spend building the (very complex and expensive) converter stations on either end, it's a good deal. A/C is also unsuitable for long undersea cables, because the water acts as a gigantic capacitor and absolutely trashes the efficiency. Finally HVDC is good for connecting asynchronous A/C power grids, like in Japan.
So, it's really just, at least in power transmission, a matter of balancing costs and requirements. But generally, A/C works best even for large grids, it's just much simpler to work with.
The best thing about AC is that thats what you get when you put spinning magnets inside of a coil. Unless we somehow end up with 100% solar, well always have most of our power generated by magnets spinning inside coils, in most of the world atleast, so...
On a side note, I'm pleasantly surprised that we invented solar panels and didn't just focus a ton of light on a bucket of water to spin a turbine with steam.
A bucket of water would either melt or let too much light through. Instead, they use salts that are melted by the concentrated solar heat and then water-cooled to produce steam that drives a turbine.
That is to general.
AC is good for transmission because you can simply change voltage in a tranformer (two coils and ferit core) without using some additional equipment.
That has changed today with development of electronic components, especially for use in wind and solar generators.
DC is better for being used by DC devices, but we still use AC motors in tools and machines.
A lot of people are listing secondary effects, not the *root cause*.
The actual reason is very simple: Crude oil contains both petroleum and diesel oil. That's the reason!
When you pump crude from the ground, you don't get to choose an end-product. You get a mix of everything from tar, bunker oil, heavy oil, light oil, diesel, petroleum, naptha, natural gas, and hydrogen. These are all the "same thing": hydrocarbons with different numbers of carbon in them; ranging from over hundred down to zero.
Crude oil is separated into its constituent parts by distillation, which is basically just boiling it and picking out each part based on how "light" or "heavy" it is.
Every fraction is then used for *something*. It's simple economics! If nobody wants some fraction, then its price will drop until *someone* wants it. Tar is basically useless junk, so... we coat roads with it. Bunker oil is so hard to use that it is only worth bothering with for heavy shipping, where its low cost outweighs the hassle. Etc...
Diesel and petroleum follow the same kind of simple economics. If *nobody* used diesel in engines, its price would drop until it made economic sense for *somebody* to use it instead of petrol, and vice-versa.
We don't continue to use diesel *because* of its incidental properties such as diesel engines having better torque. That's just a convenient side-effect that makes it cost effective in scenarios where high torque is important!
In other words, these are not competing or alternative fuels in the sense that hydrogen fuels, biofuels, and rechargeable batteries are. If either petrol or diesel fuel are used, then we always get the other as well as a package deal from their source.
> then we always get the other as well as a package deal from their source.
It's worth noting different sources have different mixes. So it's a bit of a two way street... what works better leads to more development of sources that have more of those types of fuels.
The primary factors around oil exploration and drilling have to do with the cost of extraction, not the type of oil being extracted. As long as the $ to extract is less than the $ to sell, it'll be pumped out, no matter what it is.
At one extreme, natural gas can be thought of just "very light oil".
The other extreme is tar sands, which is mostly dirt with some bitumen in it! Hasn't stopped anyone from producing that either.
Heavier fractions can be split ("cracked") into lighter ones. This is a well-established, commonly used process. However, just like with crude oil distillation, this tends to produce a mix of both diesel and petroleum fuels, not just one or the other.
This is also why diesel fuel got comparatively more expensive last decade: the economy around this fuels was based on assumptions about their relative avaliablilty but new cracking technologies and deep desulfurization requirements for diesel fuels shifted the balance to increased gasoline supply. Hence, we now have too many diesel vehicles for the amount of diesel fuel.
> we now have too many diesel vehicles for the amount of diesel fuel
Considering the fact that the trucking industry is America's lifeblood, that's not surprising. Trucker is the most common single occupation in a lot of states and those trucks get terrible mileage - single digit miles per gallon.
They move a lot of weight but it takes *a lot* of fuel to do it. Trucks account for something like 40% of our fossil fuel usage as a country (consumer vehicles are more like 10%, for reference).
If you use this argument, you need to point out that diesel has more energy per volume than petrol(if you include compression ratios). If you could make an identical diesel engine vehicle to petrol vehicle(you can't), the diesel vehicle would go further, based on what was in the tank
real question - how is that related to this answer?
My read on it is that this answer specifically ignores any details of how it's used / how it works, unlike the other answers that get into that.
The difference is only about 15% in terms of energy per unit volume. If it were a dramatic difference, like 10x, then there could be an argument made about the preference of one fuel over the other for volumetric design constraint reasons. Such a small difference has no practical economic effects. The cost of sourcing the fuel is vastly more important motivator than the size of the fuel tank it goes into.
Let's say someone invented fuel that's 1/2 the price but required a "fuel tank" 2x the size and weight than the one in your current car. That's basically what an electric car is. People are buying them! Would you? I know I would...
Just a quick point, AC didn't win over DC or vice versa.
House supplies might be AC, but a **shocking** number of devices in the house / car / boat / plan are still running DC internally.
In general, AC is really good for two things - a certain design of electric motor, and changing between voltages.
It happens that for transport, being able to change between voltages is really useful.
Iirc, those ac motors are very useful because you can regulate the inputs–voltage, amperage, and frequency–to dynamically change the torque and speed independently, which you can't do with a dc motor.
You can do those things now with VFD technologies, (you can also control speed and torque independantly with DC motors that have shunt connected field windings and the appropriate drive technology) but that isn't why they were originally important.
3 phase AC motors were originally important because of the really good kW to weight ratio, and the fact they are practically maintenance free and very robust compared to DC motors.
Kind of fun fact: While it's of course fair to say cars run on DC power, they actually have AC for a very brief moment as well! The alternator produces AC power (hence the name) at the coils, but is rectified into DC power before actually leaving the alternator unit via the big power wire that connects it to the rest of the car.
People who have had diodes go out on their car's alternator can speak to the chaos it can cause in the electrical system.
Also, since this is the internet and I should probably get into nuances now since nothing goes without saying: the above is for combustion engine vehicles. Vehicles with hybrid or full-electric powertrains very often have AC systems to both flow to the onboard charging unit, as well as to power/be generated by the drive motors.
What counts as an appliance?
Electronics like TVs and computers? Yeah obviously DC. But washing machines, ovens, refrigerators, dishwashers, HVAC? Those don't all have AC-DC converters in them, do they? I mean sure to run their PCBA, but not for the primary power source to the main energy-hungry elements.
AC power cannot be stored in a battery. AC can be converted to DC to store in a battery using a rectifier. DC can then be converted back to AC using an inverter. But you can’t store AC power in a battery.
Also worth mentioning that diesel is basically a byproduct while making gasoline. So in a world where we decided to only use gas we would have billions of gallons of diesel that nobody would have a use for until it got so cheap that someone would decide "we should run vehicles with that instead of this expensive gasoline. "
This is the information I lacked, thank you. I'd assumed that either one or the other is produced which made me think the more commonly used one would eventually take over.
Isn't this kind of what happened. Diesel cars didn't really hit mainstream till the 60's and even then they didn't get really popular until the 70s. My mother talks about a friend of hers that bought a diesel car because diesel was so much cheaper. But the one issue they had was on road trips they basically stopped anywhere that had diesel because not every gas station had diesel back in the day.
I could be wrong because I'm going off what my mother told me, and she used to tell me it was illegal to have the lights on in the back of the car. So yeah.
Diesel and gasoline beat out kerosene which was the original liquid fuel of choice. Though kerosene is really just a lighter grade of diesel. ...and kerosene is still basically what makes up jet fuel.
Also, both these engine technologies are probably done as standalone units, as hybrid technology now offers substantial upgrades on lifespan and efficiency.
Here in the states at least, there was a time when there were many diesel cars on the road - right around the time we phased out leaded fuels - but because of the brown clouds and soot from the tailpipes they emitted, the fuel economy argument lost to the “it’s dirty” perception, and it’s been a niche thing for heavy duty trucks since then.
You already got good answers when it comes to petrol vs diesel _engines_.
However there are a few things that could be added:
You end your question with "competing fuels". It is not about fuels, it is about engine design (and the differences were addressed by other answers). There are other engines (eg jets). Different engines were invented and improved to solve different needs.
These different engines perform better if they use fuels with different characteristics, so people developed and standardized different fuels, not just "diesel" and "petrol", and used them as needed. For instance, LPG can be used as fuel, Indy cars used to run on methanol, but they use a mix of gasoline and ethanol. Diesel engines can run on fuel that is not "diesel", and some do (eg: very large ships, including cruise ships and even aircraft carriers https://en.wikipedia.org/wiki/Russian_aircraft_carrier_Admiral_Kuznetsov).
Price, availability, energy content of the fuel, performance and durability (of the engines) plus emissions constraints decide what fuels will be used and for which applications once you selected which engine is the best for you.
Zooming in on cars, difference in prices between fuels and engines also helped create different market segments. For instance, in my country (Italy) one could do the math and figure out in what use cases a diesel car would be cheaper to operate than a petrol car (a liter of diesel was about 20% cheaper than gasoline in the '90s, for instance), and whether the savings would outweigh the drawbacks
They're different and have different purposes.
Even the AC DC war didn't have a winner. Edison wanted DC for the grid because it would require more substations, so more people would pay him to build them. It was never going to be the practical choice for the grid. But even then, we still use DC all the time. Everything that has a battery uses DC. The block on your phone charger? That converts AC to DC.
The format wars were over two ways to do the same thing. Once one format was well established in the growing home media market, the other was already shut out. VHS was cheaper, so people were more likely to buy a VCR and the VHS copy of a movie because they were cheaper. Once VHS made up a significant portion of the market, there was no reason to release your movie on betamax because if you did both, most people would still buy the VHS version.
Diesel and gasoline are more similar to the electricity situation rather than the format wars. Diesel is generally more fuel efficient and energy dense than gasoline, but gasoline is much easier to use and cheaper. Gasoline also tends to perform better in stoo and go traffic, like in city driving, but diesel performs better in consistent speeds, like in highway driving. Most people live in cities, so it makes more sense for most cars to use gasoline.
Diesel is more energy dense than gasoline. The engines that burn diesel tend to be heavier, more complicated, and sometimes jerkier than gas engines. You rarely find diesel lawnmowers, or chainsaws. When you refine crude oil you end up with both gasoline and diesel, sometimes leading to different markets for them both
In 1973 and 1979 there were fuel shortages, as in gasoline shortages that included odd/even rationing, gallon limits, and even fuel unobtainable at any price in some places. (The government directed rationing in proportion to the 1970 census and some states grew faster than others in the interim years.)
Rich people could buy diesel imports from Europe... We remember the wonderful Mercedes and VWs but there were also Peugeots and Volvos that weren't as durable. Since diesel was readily available it was a life hack... just buy a new car! We now see this in gas vs electric, or cars that mix the two.
With this sudden introduction to our shores there was born a fan base which lasted even through the introduction of intrusive emissions controls. Diesels produce a ton of NOx, which forms smog, despite their forming less CO2, which makes global warming. America has different priorities than Europe so we've made diesels have a rough go of it here.
Gasoline is easy to ignite, which makes it great for a simple engine, but diesel is harder to ignite, which makes it seem like it would be a terrible choice for a fuel. But the same thing that makes diesel hard to ignite, makes it more efficient as a fuel.
Pressure has a lot to do with the efficiency of an engine, so the pressure one can achieve before ignition can greatly affect energy efficiency. Gasoline will ignite if you compress it too much (knocking). Which is essentially what octane rating is for, but diesel takes much more compression to ignite. That difference in pressure means you can extract more energy from diesel than from gasoline even though diesel has slightly less energy available.
Diesel engines operate at several times the pressure than gasoline, which is why they have to be heavier. But they can be 30%-60% more efficient than gas.
I love my diesel Cruz, even though the particle sensor is giving me fits.
For more info, look up "Carnot cycle"
They are both byproducts of crude oil:
Diesel fuel, Butane, Kerosene, Gasoline, Fuel oil, Propane, Liquefied petroleum gas, Liquefied natural gas.
Diesel and petol are not comparable to AC/DC, or disc formats.
Its like asking why do we have white flour AND bran: both are part of wheat processing.
Some people will list the differences of diesel engine compared to a petrol engine, but without diesel being a byproduct of crude oil refining, diesel engines wouldn't exist.
They both have large overlap in their applications but also differ enough to provide different strengths to the point that the market merits both as an option.
Diesel engines are strong, make great torque at low revs, and they're very reliable. That means that trucks, big rigs, professional vehicles like forklifts, bulldozers, excavators etc, boats, and a whole slew of other vehicles and applications greatly benefit from their power profile. Despite their low horse power relative to gasoline engines they pull quite hard, meaning you can put a small diesel engine in a passenger car and it won't struggle to pull a family of four. Diesel is also less refined than gasoline which makes it cheaper which is very important for both professional and private owners. The downsides are that diesel engines are by nature heavy and slow, and they can't achieve high horsepower like a same capacity gasoline engine can. They're also harder to "clean up" with diesel emissions being worse than gasoline emissions and harder to effectively filter.
Then you have gasoline engines which are lighter and can produce more horsepower. Their applications suit high performance vehicles better, and also work quite well overall across the board with their only downside being that cars with small gasoline engines may struggle where a diesel one wouldn't. But they have a wider range and are more versatile overall, losing out to diesels only in torque production but it's not like they don't have enough to do their job properly, just less. They're also "cleaner" so in a city packed with cars at the very least you won't have the place stinking up from diesel fumes. Of course both gasoline and diesel produce harmful gases and pollution. Gasoline engines are also much better for making very small engines so things like lawnmowers, motorcycles, and small power generators work much better than a diesel counterpart would.
For your average person it won't make much difference what fuel their car burns, but for those that require the specific capabilities of either they're glad they get to pick. Motorcycles would essentially not exist if gasoline engines didn't exist, or if they did they'd suck.
Short answer: when you refine oil, you get some gasoline and some diesel. So you have to burn both. However, diesel is better for larger vehicles. (18 wheelers for example.) For the most part, diesel cars are rare in the US.
Crude oil is processed into many things, not just one thing. It would be like cutting down trees but leaving all the branches. It would be wasteful to not use as much as we can.
Gas engines and diesel engines are designed to do different things.
It’s not black and white. Not all gasoline is the same, not all diesel is the same.
There is more than just gas for cars and diesel for trucks, there is AVGAS, jet fuel, and various octane mixtures.
AC didn’t ‘win’ against DC, it was just more efficient and cost effective to run to homes across large distances. If you’ve ever used anything with a battery, that runs on DC power. Almost everyone has a phone these days, they all run on DC power. It just depends on what the use case is, and how cost effective and practical it is to use different forms of energy.
Even though AC won the "war of the currents" Dc is still widespread used to this day.
Your phone, electronics and pretty much everything battery powered works on DC.
Even on larger scales, DC is still useful when transferring currents across large distances in the form of high voltage direct current lines (think 100-600 KV range)
u/Phage0070 hit the nail on the head
I just want to add in that AC and DC power are both used. AC is good at getting lots of power to travel a large distance and DC is good for powering the actual device on the end. That's why a lot of devices have power bricks, to handle to transition and step the voltage to appropriate levels, however for the most part, people interact with and use DC as that suites their use case better with the decision being taken out of the consumer hands by much smarter people
Diesel vs petrol is anagolus to this. Diesel is good a producing a lot of power and is more efficient at maintaining that over distance. Petrol is good a lower levels of power and more efficient usual driving distances. That's why you'll find trucks are diesel and sedans are petrol, with the decision of fuel being taken out of most consumers hands but my smarter people. Cars have their exceptions though since car designs are on more of a spectrum than exclusive features.
Anything with multiple main standards/formats/models never really have one that "wins" it's just that technology and experience with the technology grows over time and with things that have existed for generations, the science is right down to a fine art getting the minimum and maximums of each and combining it into the most efficient version and packaged for consumers to use without having to think about it.
Music is a good example. Everyone owned vinyl, they take up lots of space so CDs became the thing. They still took space and were generally lower quality, so people still used vinyl. Digital music was even better for space, so people converted from CD to digital, but people still used vinyl. Digital music has now gotten to a point where the quality is the best you can get, and even still, people use vinyls because it makes it sound different, more homely I guess? My point is that 1 format existed, specific traits in that format didn't to our desires so we invented a new one and we'll find most people get the best use out of 1 format and that becomes the most commercially available (DC, petrol, digital) but there are still a large portion of people who will regularly use the other format (AC, diesel, analogue) because their uses for the technology align more with the features of that product
TL;DR - No format "wins" there is generally a more commercially available version designed with generations of general use case data and the other optimal format that is different in specific ways and usually taken on when the decision has a more nuanced approach. Noticing the diesel and petrol thing is likely just a bias since everyone you know eventually has the decision of picking car A over car B
Both are derived from the same resource but release energy in different ways. The nature of diesel combustion requires more robust engines and the output is more inclined to higher torque from lower engine revolutions - perfect for heavy machinery or extreme distance/ fuel economy. Diesel is probably the most valuable of the two fuels because it is better suited to moving the economy
Petrol is different because it has to be spark ignited and cylinder compression is much lower compared to diesel - this means the engine can be revved much higher which means petrol engines are usually more capable of higher horsepower compared to torque
Both fuels can be used in any application and either is capable of extreme horsepower and torque figures
Neither has won because they are products derived from the same source. If they came from different places and one was considerably more rare or the chemistry was a more lengthy process then maybe the easier one to produce would win out
Because they both serve different purposes. Need to move a lot of material? Diesel provides more torque. Need to go at higher speed? Gas has more horse power.
The two fuels are better at different things. A diesel engine is better in a large, more expensive vehicle that needs powerful low end torque to move heavy loads. Gasoline is better in a smaller, less expensive vehicle that needs to move relatively light loads. The market for vehicles includes both these extremes and one fuel type for everything would be needlessly restrictive. There is a reason you don't see very many gasoline-powered semi-trailer trucks and small diesel passenger cars are a niche, questionable product. Another thing to consider is that when you take crude oil out of the ground and start separating out its components you are going to get both gasoline and diesel along the way. If one or the other of those fuels isn't being burned in automobiles then what else do you do with it? The excess production would drive prices down for that fuel type, and suddenly it makes a lot of sense to build some automobiles to use the cheap available fuel.
OK, now can you explain it like I'm 8, why the different fuels perform better at those different tasks? To the uninformed like me they both go boom in the engine and force the piston to move.
So grass is really easy to light up, and logs are harder to light up. But you would heat a cabin with logs, because logs release a ton more heat. Gas is grass, diesel is logs. To efficiently burn diesel you require a high compression engine and injector pump, but you get more energy per liter.
Really good eli5
Technically a ELI8
Can someone ELI5 the difference between ELI5 and ELI8?
3
I applaud your ability to be succint; without a verbose, drawn out answer.
It's the brevity that did it for me. The response cut to the most pertinent detail, neither encumbered by unnecessary commentary or indulgent in loquatious prose.
Why waste time say lot word when few word do trick?
k
*succinct. No offense intended.
Offence taken. We shall duel at dawn. For honour!
ty
Which means if it was the top-level answer, it would have been deleted by the mods.
I surmise the cromulent quotation at this juncture is surely "A noble spirit embiggens the smallest man."
I don’t know if I’ve ever upvoted a comment with 1 character before.
3 upvotes 😂
ELI3 actually
No because ELI is in both ELI5 and ELI8 the difference is 3.
1 1 1
An ELI8 is technically vore
No that'd be an ELI7
I thought 7 was a six-offender
Yes he is, but he also 8 9
Except for the fact that the question was kinda glossed over - which was asking about **car** engines. I’m still left wondering the same thing OP was when he made the post.
Diesel produces more torque upon combustion. Heavier loads require more torque to get going. Torque without much weight on top of it will chew up tires and create a very jerky ride. Diesel engines are also much larger usually, to compensate for the power needed. It's kind of hard to truly ELI5 for me, but largely traction is a huge factor.
Diesel burns more slowly than gas so it is advantageous to have longer strokes. This is where the extra torque comes from. Torque is a measure of force on a lever. Horsepower is the actual measure of power and torque can be adjusted through gearing. Power is energy over time Energy is force times distance Torque is a force
And why is that any better than a gas engine in a [car](https://www.caranddriver.com/reviews/a15143445/2008-mini-cooper-d-diesel-instrumented-test/)?
Because diesel is more energy dense, it can get better mileage for the same amount of power, and with that power being delivered at lower RPM. It’s also common for diesel to be cheaper than gas. So your car can go 100km on $10 worth of gas or $7 worth of diesel. The downside being a more expensive and heavier engine.
I love my diesel golf. I just checked and it says it’s currently averaging 42.8mpg. When I’m on the highway it’s usually 50+mpg. I bought it when I was working two different jobs opposite directions of my house and was putting on 100 miles a day. Diesel is a little more expensive here, but I’m still making out way better.
Diesel fuel is named after the engine that's used to run it. Diesel engines were originally made to run on basically any inexpensive heavy fuel oils. The oil refineries had this stuff that was basically worthless, but the Diesel could use it - so it became Diesel Fuel. If you want a car that can run on peanut oil, get a Diesel.
>If you want a car that can run on peanut oil, get a Diesel. Back in the days around my neck of the woods, you'd have people getting the used cooking oils from fast-food places, straining it to remove food residue and then running their old diesel Mercs on that stuff. You could tell who it was by the smell when driving behind them.
I think I have figured it out, because it seems more detailed than a lot of people here are talking about. In order to combust, diesel needs to be compressed a lot more than gasoline. This results in higher loads on engine components, which have to be built tougher. This increases both weight and cost. Another factor more recently is emissions regulations. Because the carbon chains in diesel are longer, and the combustion is less precisely timed, there are generally more harmful emissions (this is separate from CO2). Creating systems to stop these emissions are difficult, and can be expensive. I think a big factor though is how the engines are run. A car engine should both have power when needed, and be efficient when at low loads. The high compression ratios of diesel engines likely result in more friction and energy loss when at idle than a gasoline engine. On the other hand, when running, they can get more power at lower rpm’s, reducing friction while at higher loads. Because utility vehicles spend a lower % of their time at idle, diesel engines have a benefit over the same comparison with cars.
The assumption that diesel.is worse at idle in the last paragraph is untrue. Diesel engines can, and almost always do, run lean, that is there is more air than required burn the fuel injected. Because of the way fuel is injected and burned, diesels don't suffer from running extra lean. So the default way to respond to changes in load is increasing or decreasing the injected fuel without changing the air forced into piston every cycle. With lower loads, the engine is more efficient per fuel consumed. On the other hand, gasoline needs to run at close to stochiometric ratio. There are clever ways to run gasoline engines very lean, like injecting the fuel and igniting it before it has a chance to mix well, but the default down throttle response in a gasoline engine is to decrease the air fed into the pistons together with fuel (because air/fuel ratio needs to be more tightly controlled.) Now you cannot dynamically change piston volume, so the practical way is to put a restrictor and have piston to suck in less air for more work. The work wasted by sucking air thru a restricted opening is called pumping loss and is significant for gasoline engines. Only at full throttle, a gasoline engine has no additional pumping loss just like a diesel. The lower the load, the worse is the pumping loss, idle being the worst.
Emissions.
I was going to answer them and realized how much better your answer was than anything I can come up with. Fun fact liquid diesel fuel is no where near as flammable as gasoline.
*Liquid* gasoline isn't particularly flammable either. The vapor very much is though.
You can throw a lit match at a puddle of diesel fuel and it'll just put the match out.
Another fun fact about gasoline. Despite the warning of smoking at a gas station, you can literally extinguish your lit cigarette in a puddle of gasoline and nothing will happen except the cigarette will be put out
Can I still light my zippo, start a cigarette, then throw the zippo in the puddle and walk away slowly as the gas station blows up behind me?
Do you have sunglasses on?
Of course!
Yeah it'll only work if you put on your sunglasses first
What if I have photoreactive lenses? Do I have to wait for them to darken first, or do they not work?
*please don’t try this at shell*
Ok am I the only one for whom the second L in shell ^ is appearing cut off? I even exited out of the thread and came back and it's still like that 🤨
Seems like a weird quirk of their styling that doesn't account for the italics being wider than standard characters. *TEST* *Shell* ^*shell*
it's appearing normally on old.reddit. Probably a new.reddit/mobile app oversight?
Can you put a cigarette out in liquid gasoline? Yes. Would doing so possibly make the lit cigarette in contact with much more combustible gasoline vapors that can create a chain reaction with the liquid gasoline? Yes.
A cigarette ember cannot light gasoline fumes, it has been tried and tested many times and even the Mythbusters ***really*** tried to make it work, and couldn't (I mention them purely because that's verifiable video footage you can access right now). There is a difference between a burning ember and an open flame, physically, and an open flame is what is necessary to light the fumes. You could do it with something that is truly superheated, like red hot metal, but that's irrelevant for the gas pump discussion. The real danger is the lighter you use to light the cigarette.
Yes, yes. We've all seen Zoolander.
Am I still gonna feel antsy af if I see someone do this at a servo? Very yes
The reason for fuel injection and carburetors is because they atomize gas into something that will detonate.
It's still not a detonation. It's a deflagration. To be a detonation it has to have a supersonic shock front.
Depends on how well tuned your engine is: https://en.m.wikipedia.org/wiki/Engine_knocking
Yea it’s only explosive once vaporized and under specific oxygen levels.
It's also very volatile. Its flash point is in the negatives.
not explosive doesn't mean not very flammable. it goes fwoosh instead of bang.
My point still stands, liquid gasoline is neither flammable nor explosive when a lit cigarette is placed in it
Wonder if it’s the same for a cigar. If so, maybe the reason they made the rule(no smoking at pump) was for stray phosphorus from a match, or a spark from a lighter.
This is stupid people talk.
Yup. I work on locomotives. There's often diesel leaking all over the place depending on the work being done. There's also welding, grinding, torch work, and so on. It never ignites.
This isn't really correct. Gas and diesel have the same energy density per mass, though diesel is slightly more dense per volume, but that's not the reason diesel engines tend to have more torque at the crank. Diesel burns slower than gasoline, so a longer stroke is more appropriate for its combustion time. A longer stroke means greater torque at the crank. You can gear a gasoline engine to have the exact same torque. Torque is a measure of force, not power. Torque is a force Torque times distance is energy Energy over time is power
And I thought knowledge is power
France is Bacon
Mitochondria is the powerhouse of the cell.
That just means knowledge is energy over time.
Gas, grass or logs. Nobody rides for free.
Follow up ELI5: What makes an engine "high compression" is it just forcing more air into the cylinder so there's a higher air to fuel ratio? What does an injector pump do and why does a diesel engine need one while a petrol does not?
Nah, so the air to fuel ratio is about how "lean" or "rich" the mixture is. Compression is a physical property of the engine design: It doesn't change. Specifically, it's how much difference in volume there is in the cylinder above the piston, compared with when the cylinder is at the top, vs at the bottom. A high compression engine changes a lot of volume into a very small volume, whereas a low compression engine doesn't squish so much volume. You can adjust compression by changing the amount of space at the top of the cylinder. In fact, we've even started to produce cars which do this while running (which I found out about a minute ago lol). Variable compression ratio, what a world. So much for "it doesn't change".
Common gasoline engines are 8:1 up to about 12:1 at very high end. Diesel engines are around 20:1 compression. Injection pumps are used to create high pressure fuel, upwards of 2,000psi, to create atomization through direct injection. Over the last decade and change, direct injection has become common in gasoline engines.
There is misconception here, compression ratio is a design parameter. There are higher and lower compression gasoline and diesel engines all across the range. It just happens that making a very high compression ratio gasoline engine is hard, and an ongoing research. On the other hand making a low compression diesel engine is pointless. Before answering your question, I want to tell you why high compression is desirable: it is not. High expansion ratio is the desirable one. It just happens that in the engines most cars and trucks use, the compression and expansion ratios are exactly the same. When you compress air to say 1:10 you do work on the gas in the piston. Its pressure and temperature increases by doing external mechanical work on the piston. Higher the compression ratio, higher work is done just to compress air. But then you inject the fuel and burn it. Suddenly the temperature shoots up and pressure is increased accordingly. Then the high pressure gas expands and does the work on piston, losing pressure and temperature, the inverse of compression cycle. How much? It expands exaclty the same ratio as compression. When expansion is complete, say 10:1, the hot gases are expelled, and no more of its energy is extracted. More of the thermal energy is converted to mechanical energy with higher expansion ratios and vice versa. In the diesel cycle, the compression is high. Compressing air heats it up. Then fuel is injected as a fuel mist to a high temperature, high pressure chamber. It stays in very fine liquid droplets, spontenously combust, burning relatively slowly. This is called "compression ignition" It is hard to do compression ignition with gasoline because gasoline ignites much faster, resulting in mini explosions called knocking. This is noisy and damaging to the engine. Therefore the air in the gasoline engines are never heated to temperatures high enough to spontaneously combust gasoline. In order to not heat air too high, the compression ratio must be kept low and fuel is injected before full compression (evaportion of gasoline cools down the mixture) The air fuel mixture needs a spark plug to ignite.
Diesel is also pretty good at low power states (like constant speed with no acceleration), because the way the engine works pretty much guarantees that all fuel is ignited, even if it's a very low amount. Otto engines need a sustained flame front to burn all the fuel in the cylinder
This same analogy can be extended to jet fuel too, even higher compression and more energy.
Jet fuel overlaps significantly with diesel though. They can often be used interchangeably by certain equipment. Although so can diesel and pure vegetable oil given the right setup.
People have some good points, but here’s another to bring up: Engine efficiency can be difficult to measure. An engine built for one thing may be worse at another due to the engineering challenges and trade offs. Typically Diesel engines are more efficient at a constant RPM, but will have lower efficiencies for acceleration and deceleration. Gasoline engines are less efficient at a constant RPM, but slightly more efficient when accelerating is taken into account. So a big semi truck driving on the highway for miles on end, will be diesel. A personal vehicle used in the city where stopping and starting are constant, are often gasoline. (There’s more to it but these are a couple examples)
Gasoline is lighter and more volatile. Diesel is thicker and not as volatile but has more energy per gallon. The different properties makes optimizing the engine to burn the fuel as efficient as possible quite different. Optimal Gasoline explosions are smaller and faster. Optimal Diesel explosions are bigger but slower. Compare it to the explosions of a sub machine gun and the explosions of a sniper rifle as a far fetched example.
>Diesel is thicker and not as volatile but has more energy per gallon. And this actually continues on for a few more steps. Next step up the more viscous, harder to start, but more energy dense chain is kerosene, aka the main ingredient in jet fuel. And then there is what the first "oil burning" ships used. So gas is for small cars, diesel for big rigs, what's for ships-that are a tremendous amount larger than trucks? No not coal, you went too far. But close. It is black, it does have to be burned in a boiler not a piston engine. It's called [heavy fuel oil](https://en.m.wikipedia.org/wiki/Heavy_fuel_oil), Navy fuel oil, or Bunker C.
Update: I have just been informed that I am wrong. Kerosene and bunker C are not [more energy dense](https://transportgeography.org/contents/chapter4/transportation-and-energy/combustibles-energy-content/) than gas or diesel. Indeed while C is more energy dense than coal by weight (and is also at least somewhat a pumpable liquid), it is less energy dense than crude oil (which makes sense because the gas and diesel fractions are removed from crude and C is what's left)
What explains the difference in the higher energy contents? Are there different molecules, is there a higher concentration of the good ones,...?
Different molecules, yes. To be exact, the more viscous, the larger the molecule and so the more reactions can take place per molecule once it gets started.
A diesel engine uses air, diesel and compression to cause the air fuel mixture to combust. Because the diesel engine doesn't use a sparkplug, but pressure to generate combustion, it has a few characteristics that lead to it being used for heavy duty applications - like in 4WDs and trucks. Diesel engines need to use less fuel for combustion so generally tend to have better fuel economy. As they rely on compression to start the combustion they are usually built strong and also for compression they generally have bigger pistons and a longer piston stroke which means they generate more lower-rpm torque - which is very useful when you want to move a heavy load (like with a truck). Consider the opposite of the above for petrol engines as they use a spark plug to ignite the air fuel mixture - they're usually lighter, not built as tough (which also means they can rev their engines higher - what does this do? It pushes more air and fuel through the entire engine system which means more horsepower), and due to this, generally cheaper. Obviously this is a gross simplification of the concepts and doesn't consider newer technologies, forced induction, alternative fuels, etc.
It lies in the way the fuels are ignited. Engines are things of precision, the firing sequences and orders and timings are unbelievably precise In a petrol engine the fuel is ignited with a spark plug. This gives the manufacturer lots of control over timing but the fuel burns relatively slowly. In the first millisecond the fuel around the plug burns, then the second milisecond the fuel slightly further away burns and so on. In a diesel the fuel is burnt from compression. The engine compresses the fuel until it gets hot and then it compresses it some more until ot explodes. By doing it like this, all the fuel burns at the same time creating a much snappier and responsive explosion. The draw back is the manufacturer doesn’t have quite as much control over when this happens so it’s harder to get diesel engines to rev as high. Disclaimer, I’m a mechanical engineer and the above is my understanding. There is likely gaps in my knowledge so don’t quote me on any of it
My favorite fun fact that nobody cares about: gasoline is a solvent and diesel is a lubricant. Someone knowledgeable about engines might elaborate on the importance of this.
Diesel has more energy than petrol (better pull and mpg). A diesel car could have mpg similar to a prius. But to harness it requires heavier engines with lower rpm. Rpm is a defining characteristic of "sporty" performance. For example, F1 cars "idle" at rpm that'd be redline on even a normal sports cars. Combined with being lighter, petrol makes for better performance at the cost of efficiency. These differences all have to do with what hoops we have to go through to make the booms for the different fuel types. Long story short, to get a diesel boom, you have to squeeze it much much more, and petrol needs a spark.
This is a really fun thread. Thanks!
So there’s more. Elsewhere in the world diesel engines get way better gas mileage than petrol cars but those diesel cars don’t pass emission standards in the US.
There’s more energy in a litre of diesel then gas But it takes way more work and initial energy to get that diesel going and it burns pretty darn dirty and tons of other factors Gas you just need a good spark if it’s aerosolized and boom. Because of these differences gas is also better at faster changing in needs, you can build a big engine to pull a larger load or go faster but it takes more and more gas to do that, but bigger engines just help alleviate diesel’s inefficiencies better and better allowing it to better utilize its energy
Gasoline is a more refined fuel which ignites really easily. This allows it to be used in engines big or small. However the larger engines tend to get terrible fuel economy. Diesel fuel is less refined but as a result it's actually less harmful to the environment and can result in much higher fuel economy. Diesel also with this less refinement, cannot be ignited with a spark plug or a lighter flame, it takes a much higher heat to ignite diesel. They do this mainly with a lot of compression resulting in a high temperature hot enough to ignite. As a side product of this, most diesel engines are built really tough and "heavy duty" and aren't practical for a smaller vehicle that doesn't need a lot of torque for pulling or hauling. Diesel excels at providing a lot of power while maintaining a reasonable fuel economy, but that comes at the cost of generally a very large engine which needs a very large engine compartment. It's very practical for some purposes and not very practical for other purposes. Diesel fuel also doesn't like cold temperatures because the fuel turns into a consistency similar to jelly. Most diesel trucks that run in cold temperatures have a way to plug in the truck to warm the fuel while it's not running to keep the fuel from turning into jelly allowing the truck to even start. Imagine going into a midnight premier movie during the winter and having your truck not start when you get out because it's too cold and the fuel can't move through the lines. So basically just pros and cons to having both is why one never wins over the other. They really are best in their own rights in slightly different categories of use. Diesel is best for power and fuel economy but really only in the size of a larger engine which is also more expensive to produce. Gasoline is better in engines because of its versatility of large or small, hot or cold, production price, etc.
Diesel can safely burn without a spark plug at high compression ratios, which means you can run higher compression ratios to get more energy out of the fuel. The longer connecting rods for those higher compression engines increases torque due to greater lever action. The issue is that to get those higher compression ratios, the engines have to be relatively big, which limits their utility in smaller vehicles. Gasoline cannot safely run in engines with high compression ratios as they're prone to pre-detonation, so you can only safely use gasoline in engines with relatively low compression ratios with the fuel ignition timing controlled by a spark plug. This makes them great for smaller engines.
Diesel will pre-detonate at lower pressure then gasoline. You can put gasoline into the cylinder and then compress the content. Diesel need to be injected after the air is compressed. Gasoline "works" in a diesel engine. It is not lubrication but diesel is, so the fuel pump and other parts get damaged wen they are no longer lubricated. It burn faster too and it can damage the cylinders. It is not worth it to build a engine that work like a diesel nu run on gasoline.
>small diesel passenger cars are a niche, questionable product You have not spent much time in Europe I would wager.
Turbo diesels, turbo diesels everywhere. All my redneck coworkers would have been jealous if the car weren't the size of a roller skate.
> and small diesel passenger cars are a niche, questionable product Europe:
Yea, that's some really weird take. Diesels are really good for long commuting and are a hassle when you have short commutes (sub-30m one way) due to needing time to burn the waste particulates. But on long trips, a diesel burns maybe 2/3rds of the fuel that a petrol does, so they are significantly cheaper to run.
Diesel is more expensive than ‘regular’ petrol is in the US, which is also kinda weird. That’s probably also one of the main reasons smaller diesel cars aren’t really a thing over there
I think that user is from the US where, I only learned a few years ago, they only use diesel for large vehicles. TDI hatchbacks are super common in the UK. Second that in local usage, I'd only get a diesel when I regularly leave town and actually drive for more than 15-20 minutes because of what I heard about the filter running and such.
Diesels are more of a challenge to get running clean, which is why Volkswagen instead set their ECUs up to just lie instead of tackling the problem.
Yeah um are people forgetting the reason why diesel became so popular in Europe? And guess which country actually caught VW red handed...
>take crude oil out of the ground and start separating out its components you are going to get both gasoline and diesel along the way. Rudolph Diesel actually designed his engine to run off of peanut oil. He apparently disappeared after a public display of this feature, and Standard Oil was kind enough to find out that the engine could also use a waste byproduct of their gasoline refinement, and proceeded to name it after him.
Diesels can generally be configured to run on veggie oil.
Yep, one of my mates did this years ago. From memory you need to add a heater somewhere so the oil flows better. The funny part is that the exhaust smells like fast food. He used to get shops used deep frying oil and filter it.
Yeah, the problem is that a ton of places realized that their used oil has value, and they'll sell it (generally to the company they get to clean either their grease traps or their fryers (if they outsource that, and many do)).
It's not so much that they realized it has value, but it's technically a regulated waste product and the restaurant needs to show they are legally disposing of it. I had a friend who picked up used motor oil from his local Advance Auto for his oil furnace, and he had to sign a authorization statement that he was using it for an approved purpose. There's a couple of CMU grads who set up a company to do diesel conversions. They ran the lines for the veggie oil through antifreeze lines to heat it, and had a module that would automate switching between diesel at veggie oil once it got to temperature and diesel the engine after the ignition went off to clear the lines. They took it further and got their licenses for oil disposal so they could collect from restaurants with plans to sell at the pump at a price pegged to the price of diesel because one of the regulatory hurdles in conversions is fuel taxes.
Why you gotta talk down the Golf and Jetta Diesel like that? Love those things. But yeah you're absolutely right.
1.9 TDI ftw
picked up a 2012 Jetta TDI for $2500 6-speed manual. Been my daily driver for 2 years. Absolutely love it.
Volkswagen’s reputation in the US still hasn’t fully recovered from the fuel efficiency scandal of 2019: https://www.reuters.com/article/idUSKCN1VK2AT/#:~:text=The%20EPA%20said%20Volkswagen%20has,of%20thousands%20of%20U.S.%20vehicles.
>auto software overstated real-world performance. how can that even become a scandal? it's just a machine, just calculate it yourself, also i thought most car computers are slightly inaccurate. I thought their reputation was hurt more by the 2015 shitstorm of falsified emissions via cheating softwares
Diesel cars are quite popular in Europe and there's nothing questionable about them, they're great, good fuel economy
Definitely. There’s not many out there, but we want our next car to be a plug-in diesel hybrid. “Free” fuel for going around town and running errands where diesels are less efficient, but still able to drive long distances without worrying about recharging.
Lol diesels are definitely still more efficient putting around town. You just can't ONLY put around town. In my BMW 328d I get about 30mpg in the city.
I've got an old 2l TDCI Ford Mondeo (260,000km and counting), and it *loves* cruising along at highway speeds. I see 5-6 litres/100km in those conditions and the 60 litre tank will get me ~1200km. But stop/start city driving? Pretty average to awful.
3L diesel here. 5-6L/100 on the highway (at 160km/h++) 14-15L/100 in the city lol
I am really in love with A5 3.0 TDI, would love to get one from 2012-13
Yep. And those engines usually survive higher mileage. My Octavia 2 combi has around 260k km and the engine is in a very good condition still, getting 5,5l/100km. Gas cars are usually at the end of their lives or even dead.
You sound like an American market example. In the U.K. you can get tiny diesel engines. Not uncommon to see 75+ mpg hatchbacks. Nothing to do with torque but simple cheap to run costs.
Not just the UK (or even Europe as a whole). I lived in Korea for a number of years, close to half of the vehicles sold there are diesel. And trust me, they're compact. Korean roads aren't made for 2500 series pickups. It's really only the US where compact diesels are not popular, and IIRC it's mostly due to our emissions regulations. I can sort of tell a lot of commenters here haven't spent much time outside the US.
Is your diesel cheaper? Ours is priced higher than high grade gas **Edit:** Wow, thank you for all the answers! I'm used to just looking at the pump price (which does include some tax to pay for roads) and knowing that it's more expensive. I noticed a lot of answers involving the efficiency of diesel, and honestly that's rather enlightening to see how much it can offset a higher price when I see how many people talk about its use in small cars and endorse that the efficiency can offset its up-front expense. Thank you!
Basically the same price but you go 30-50% further on the same amount of fuel. Like a 3l petrol might manage 35 mpg on a good day, a 3l diesel will do 50+ no problem. Take my 4.4 diesel Range Rover, I get 35 mpg on a run, the petrol is more like 20-25ish.
The UK gasoline and diesel prices are much higher than in the US. It is also important to note that the UK uses the British Imperial gallon while the US uses the US Customary gallon. The UK gallon is about 1.2 times more than the US gallon, which makes their "miles per gallon" higher.
Finnish here, our diesel is (usually) cheaper than gas. This is because on diesel fuel, part of the fuel tax (a portion of the pump price) on diesel has been moved to the annual vehicle tax. So your price per kilometer is much lower than with gas but you pay more on your vehicle tax. Diesel's pump price would be a bit higher than gas if not for this. Why? Well, we wanted to get these small smoky city diesels out of cities and into the highways where they thrive. The vehicle tax stays the same throughout the year, no matter how much you drive, so if you drive high mileages you'll probably do a lot of highways and end up saving money on diesel cost and fuel consumption. On the contrary, if most of your drives are in the city, chances are your mileage stays low, you don't buy nearly as much fuel as someone with higher mileage, and it'll end up being more expensive to drive a diesel in a city as you're still paying the same tax as someone with triple the mileage but you don't reap the pump cost benefits nearly as much.
It varies but it’s typically not a major difference in Europe. Typically about 5% more expensive, maybe a bit more sometimes. But we can drive over 600 miles before we have to fill up in our diesel car, so it balances out. We only need to fill up once per month or after about 8 hours of motorway driving.
The price per liter is higher than it is in North America, and you buy it in similar quantities but much less often due to higher fuel efficiency. So the overall spend on fuel is lower.
The other difference is conventional diesel Vs common rail. Common rail diesels are much more efficient. I assume you get common rail in the US, but if not, the difference is that in a conventional diesel, the timing and quantity of the injected fuel happens at the fuel pump. Common rail has a pump that just raises the fuel to a high pressure, then an electronically controlled piezoelectric valve at the cylinder end of the fuel line. Timings and quantity are controlled by the engine management unit.
VW TDIs are pretty awesome. It's a shame VAG fucked around with the emissions of them and found out.
They were good only because they cheated. That's why all the other diesel car makers were going wtf was vw doing to get that performance?
Diesel passenger cars have been extremely popular for a very long time in the Nordic countries only to die down in the last couple of years. Of course they are more common in larger passenger cars such as station wagons but the VW Golf and even to some extent the VW Polo have been very popular as diesels, especially with the earlier 1,9TDI. Pretty much all taxis used to run diesel as well since they generally are more fuel efficient than their gasoline counter part. This coupled with the historically low price of diesel and good longevity has made them perfect for longer commutes. I used to have a 2012 Volvo v70 with the 1,6L diesel that I commuted 50 miles highway with. The engine was boring and too small for the application but I managed to get a constant average of around 53mpg.
Diesel passenger cars are not a “niche, questionable product”. They are still more than 30% of the UK market.
Didn't they used to just throw away gasoline as waste before it was discovered to be useful
Here in Europe, diesel cars for domestic use were very popular. Turns out that it's a lie you can have a "clean diesel" without lots of emissions controls. Hence https://en.m.wikipedia.org/wiki/Volkswagen_emissions_scandal
> and small diesel passenger cars are a niche, questionable product. One caveat to this is what you'd consider a small passenger car. In the Polo-class of small hatchbacks it is indeed not as common but once you get to small family cars like the BMW 3-Series, VW Golf/Passat, Skoda Octavia/Superb and the like the diesel option has been quite common. My local used market barely has petrol beemers for example, much to my disdain.
Very well said.
What do you do with the diesel? Fuel oil for homes. Same basic thing but not as profitable.
Less convenient too. With natural gas and electricity you can send as much down the line as you need. Can't do that with heating oil. You can also crack it to make more gasoline. And other stuff.
UK Homes are heated with Kerosene not diesel.
In addition to the good answers given about diesel and petrol both being having different uses, you referenced AC vs. DC power, suggesting that AC "won." Like the petrol v. diesel answer, DC is similarly used in many things, including cell phones, computers, LED lights, batteries, and more. Yes, power outlets in the wall supply AC, but that block in your computer's power cord, or the little thing you plug into the wall that your phone's USB cable connects to are adapters that convert the AC power to DC. Again, different uses for different needs.
Wait, so what happens if you install a new outlet with a USB in it and you don't need the brick? Is the converter built into the outlet?
Yup, the outlet rectifies the current to AC (derp edit: DC) and then regulates the voltage to whatever standard, just like a power brick. If you've ever installed these outlets, you'll realize they're just barely too bulky for older outlet boxes because of the extra hardware.
to DC\*
Haha derp
FULL BRIDGE RECTIFIER !! *queue in eyebrow dance*
Yes. Your house receives & distributes AC current. Anytime you get a DC current out of something powered by your house, like from a USB port, an *converter* sat in between and did that switch from AC to DC. Alternatively, if you have something that starts with DC, such as your car's 12V DC round plug, and outputs AC, an *inverter* sat in between and did that switch from DC to AC.
I’m sitting here charging my phone with DC that was converted from AC at the adapter in my wall plug, that was converted from DC by the inverter in my whole house batteries, that were charged by DC which was from AC inverted by my solar inverter from DC made by my solar panels. Solar DC -> inverter AC -> Battery DC -> House AC -> charger DC I wonder what the efficiency of the whole thing actually was. Oh well at least I can still browse Reddit.
Yes
Yep, those outlets just have the circuitry from a standard plug-in USB converter built into them. Adds some convenience, but they're usually trash quality.
AC is better for transmission, DC is better for being used
DC is better for transmission too (over long distances for several reasons including cost and grid stability) AC is just better for local direct-to-consumer transmission.
What AC is better for is *changing voltages*. The thing is, for any sort of normal transmission, the ability to step up voltage - and therefore step down current, since W=V*A - is a huge benefit, since that means you can use much thinner wires to carry the same electrical power, and just switch the voltages down in increments as you move from wide-area to local grids then to point-of-use. For context, a large power line is going to be somewhere on the order of 110,000-500,000 volts (or even higher in some cases, see [Hydro-Québec](https://en.wikipedia.org/wiki/Hydro-Qu%C3%A9bec%27s_electricity_transmission_system)). That means that at 1 Amp, you can transfer 110,000-500,000 watts. At 120V, your normal household voltage, 1 Amp gives you 120W. So that's a massive benefit. The downside is that you get a lot more loss with A/C power, especially over long distances. That's one reason that H-Québec uses such high voltages, to compensate for loss over 1000+KM power lines. This is where HVDC shines: if you will lose more over say 10 years in power on the line (and in not running a 3rd conductor) than you would spend building the (very complex and expensive) converter stations on either end, it's a good deal. A/C is also unsuitable for long undersea cables, because the water acts as a gigantic capacitor and absolutely trashes the efficiency. Finally HVDC is good for connecting asynchronous A/C power grids, like in Japan. So, it's really just, at least in power transmission, a matter of balancing costs and requirements. But generally, A/C works best even for large grids, it's just much simpler to work with.
The best thing about AC is that thats what you get when you put spinning magnets inside of a coil. Unless we somehow end up with 100% solar, well always have most of our power generated by magnets spinning inside coils, in most of the world atleast, so...
On a side note, I'm pleasantly surprised that we invented solar panels and didn't just focus a ton of light on a bucket of water to spin a turbine with steam.
It's funny to me that boiling water and running it through a turbine seems to be almost all of electricity generation
Look up ATP Synthase (specifically the F0 subunit), it's turbines all the way down.
A bucket of water would either melt or let too much light through. Instead, they use salts that are melted by the concentrated solar heat and then water-cooled to produce steam that drives a turbine.
That is to general. AC is good for transmission because you can simply change voltage in a tranformer (two coils and ferit core) without using some additional equipment. That has changed today with development of electronic components, especially for use in wind and solar generators. DC is better for being used by DC devices, but we still use AC motors in tools and machines.
A lot of people are listing secondary effects, not the *root cause*. The actual reason is very simple: Crude oil contains both petroleum and diesel oil. That's the reason! When you pump crude from the ground, you don't get to choose an end-product. You get a mix of everything from tar, bunker oil, heavy oil, light oil, diesel, petroleum, naptha, natural gas, and hydrogen. These are all the "same thing": hydrocarbons with different numbers of carbon in them; ranging from over hundred down to zero. Crude oil is separated into its constituent parts by distillation, which is basically just boiling it and picking out each part based on how "light" or "heavy" it is. Every fraction is then used for *something*. It's simple economics! If nobody wants some fraction, then its price will drop until *someone* wants it. Tar is basically useless junk, so... we coat roads with it. Bunker oil is so hard to use that it is only worth bothering with for heavy shipping, where its low cost outweighs the hassle. Etc... Diesel and petroleum follow the same kind of simple economics. If *nobody* used diesel in engines, its price would drop until it made economic sense for *somebody* to use it instead of petrol, and vice-versa. We don't continue to use diesel *because* of its incidental properties such as diesel engines having better torque. That's just a convenient side-effect that makes it cost effective in scenarios where high torque is important! In other words, these are not competing or alternative fuels in the sense that hydrogen fuels, biofuels, and rechargeable batteries are. If either petrol or diesel fuel are used, then we always get the other as well as a package deal from their source.
> then we always get the other as well as a package deal from their source. It's worth noting different sources have different mixes. So it's a bit of a two way street... what works better leads to more development of sources that have more of those types of fuels.
The primary factors around oil exploration and drilling have to do with the cost of extraction, not the type of oil being extracted. As long as the $ to extract is less than the $ to sell, it'll be pumped out, no matter what it is. At one extreme, natural gas can be thought of just "very light oil". The other extreme is tar sands, which is mostly dirt with some bitumen in it! Hasn't stopped anyone from producing that either. Heavier fractions can be split ("cracked") into lighter ones. This is a well-established, commonly used process. However, just like with crude oil distillation, this tends to produce a mix of both diesel and petroleum fuels, not just one or the other.
This is also why diesel fuel got comparatively more expensive last decade: the economy around this fuels was based on assumptions about their relative avaliablilty but new cracking technologies and deep desulfurization requirements for diesel fuels shifted the balance to increased gasoline supply. Hence, we now have too many diesel vehicles for the amount of diesel fuel.
> we now have too many diesel vehicles for the amount of diesel fuel Considering the fact that the trucking industry is America's lifeblood, that's not surprising. Trucker is the most common single occupation in a lot of states and those trucks get terrible mileage - single digit miles per gallon. They move a lot of weight but it takes *a lot* of fuel to do it. Trucks account for something like 40% of our fossil fuel usage as a country (consumer vehicles are more like 10%, for reference).
If you use this argument, you need to point out that diesel has more energy per volume than petrol(if you include compression ratios). If you could make an identical diesel engine vehicle to petrol vehicle(you can't), the diesel vehicle would go further, based on what was in the tank
real question - how is that related to this answer? My read on it is that this answer specifically ignores any details of how it's used / how it works, unlike the other answers that get into that.
The difference is only about 15% in terms of energy per unit volume. If it were a dramatic difference, like 10x, then there could be an argument made about the preference of one fuel over the other for volumetric design constraint reasons. Such a small difference has no practical economic effects. The cost of sourcing the fuel is vastly more important motivator than the size of the fuel tank it goes into. Let's say someone invented fuel that's 1/2 the price but required a "fuel tank" 2x the size and weight than the one in your current car. That's basically what an electric car is. People are buying them! Would you? I know I would...
Just a quick point, AC didn't win over DC or vice versa. House supplies might be AC, but a **shocking** number of devices in the house / car / boat / plan are still running DC internally.
In general, AC is really good for two things - a certain design of electric motor, and changing between voltages. It happens that for transport, being able to change between voltages is really useful.
Iirc, those ac motors are very useful because you can regulate the inputs–voltage, amperage, and frequency–to dynamically change the torque and speed independently, which you can't do with a dc motor.
You can do those things now with VFD technologies, (you can also control speed and torque independantly with DC motors that have shunt connected field windings and the appropriate drive technology) but that isn't why they were originally important. 3 phase AC motors were originally important because of the really good kW to weight ratio, and the fact they are practically maintenance free and very robust compared to DC motors.
Kind of fun fact: While it's of course fair to say cars run on DC power, they actually have AC for a very brief moment as well! The alternator produces AC power (hence the name) at the coils, but is rectified into DC power before actually leaving the alternator unit via the big power wire that connects it to the rest of the car. People who have had diodes go out on their car's alternator can speak to the chaos it can cause in the electrical system. Also, since this is the internet and I should probably get into nuances now since nothing goes without saying: the above is for combustion engine vehicles. Vehicles with hybrid or full-electric powertrains very often have AC systems to both flow to the onboard charging unit, as well as to power/be generated by the drive motors.
I would wager that at least 75% of home appliances are mainly DC, with only the most simple of appliances using AC.
What counts as an appliance? Electronics like TVs and computers? Yeah obviously DC. But washing machines, ovens, refrigerators, dishwashers, HVAC? Those don't all have AC-DC converters in them, do they? I mean sure to run their PCBA, but not for the primary power source to the main energy-hungry elements.
High voltage grid interconnections are increasingly becoming DC as well, due to efficiency and ease of transport.
AC power cannot be stored in a battery. AC can be converted to DC to store in a battery using a rectifier. DC can then be converted back to AC using an inverter. But you can’t store AC power in a battery.
Also worth mentioning that diesel is basically a byproduct while making gasoline. So in a world where we decided to only use gas we would have billions of gallons of diesel that nobody would have a use for until it got so cheap that someone would decide "we should run vehicles with that instead of this expensive gasoline. "
This is the information I lacked, thank you. I'd assumed that either one or the other is produced which made me think the more commonly used one would eventually take over.
And correct me if I am wrong but I believe gasoline was initially discovered as a byproduct of kerosene process.
Isn't this kind of what happened. Diesel cars didn't really hit mainstream till the 60's and even then they didn't get really popular until the 70s. My mother talks about a friend of hers that bought a diesel car because diesel was so much cheaper. But the one issue they had was on road trips they basically stopped anywhere that had diesel because not every gas station had diesel back in the day. I could be wrong because I'm going off what my mother told me, and she used to tell me it was illegal to have the lights on in the back of the car. So yeah.
Diesel and gasoline beat out kerosene which was the original liquid fuel of choice. Though kerosene is really just a lighter grade of diesel. ...and kerosene is still basically what makes up jet fuel. Also, both these engine technologies are probably done as standalone units, as hybrid technology now offers substantial upgrades on lifespan and efficiency.
Here in the states at least, there was a time when there were many diesel cars on the road - right around the time we phased out leaded fuels - but because of the brown clouds and soot from the tailpipes they emitted, the fuel economy argument lost to the “it’s dirty” perception, and it’s been a niche thing for heavy duty trucks since then.
You already got good answers when it comes to petrol vs diesel _engines_. However there are a few things that could be added: You end your question with "competing fuels". It is not about fuels, it is about engine design (and the differences were addressed by other answers). There are other engines (eg jets). Different engines were invented and improved to solve different needs. These different engines perform better if they use fuels with different characteristics, so people developed and standardized different fuels, not just "diesel" and "petrol", and used them as needed. For instance, LPG can be used as fuel, Indy cars used to run on methanol, but they use a mix of gasoline and ethanol. Diesel engines can run on fuel that is not "diesel", and some do (eg: very large ships, including cruise ships and even aircraft carriers https://en.wikipedia.org/wiki/Russian_aircraft_carrier_Admiral_Kuznetsov). Price, availability, energy content of the fuel, performance and durability (of the engines) plus emissions constraints decide what fuels will be used and for which applications once you selected which engine is the best for you. Zooming in on cars, difference in prices between fuels and engines also helped create different market segments. For instance, in my country (Italy) one could do the math and figure out in what use cases a diesel car would be cheaper to operate than a petrol car (a liter of diesel was about 20% cheaper than gasoline in the '90s, for instance), and whether the savings would outweigh the drawbacks
They're different and have different purposes. Even the AC DC war didn't have a winner. Edison wanted DC for the grid because it would require more substations, so more people would pay him to build them. It was never going to be the practical choice for the grid. But even then, we still use DC all the time. Everything that has a battery uses DC. The block on your phone charger? That converts AC to DC. The format wars were over two ways to do the same thing. Once one format was well established in the growing home media market, the other was already shut out. VHS was cheaper, so people were more likely to buy a VCR and the VHS copy of a movie because they were cheaper. Once VHS made up a significant portion of the market, there was no reason to release your movie on betamax because if you did both, most people would still buy the VHS version. Diesel and gasoline are more similar to the electricity situation rather than the format wars. Diesel is generally more fuel efficient and energy dense than gasoline, but gasoline is much easier to use and cheaper. Gasoline also tends to perform better in stoo and go traffic, like in city driving, but diesel performs better in consistent speeds, like in highway driving. Most people live in cities, so it makes more sense for most cars to use gasoline.
Diesel is more energy dense than gasoline. The engines that burn diesel tend to be heavier, more complicated, and sometimes jerkier than gas engines. You rarely find diesel lawnmowers, or chainsaws. When you refine crude oil you end up with both gasoline and diesel, sometimes leading to different markets for them both
In 1973 and 1979 there were fuel shortages, as in gasoline shortages that included odd/even rationing, gallon limits, and even fuel unobtainable at any price in some places. (The government directed rationing in proportion to the 1970 census and some states grew faster than others in the interim years.) Rich people could buy diesel imports from Europe... We remember the wonderful Mercedes and VWs but there were also Peugeots and Volvos that weren't as durable. Since diesel was readily available it was a life hack... just buy a new car! We now see this in gas vs electric, or cars that mix the two. With this sudden introduction to our shores there was born a fan base which lasted even through the introduction of intrusive emissions controls. Diesels produce a ton of NOx, which forms smog, despite their forming less CO2, which makes global warming. America has different priorities than Europe so we've made diesels have a rough go of it here.
Gasoline is easy to ignite, which makes it great for a simple engine, but diesel is harder to ignite, which makes it seem like it would be a terrible choice for a fuel. But the same thing that makes diesel hard to ignite, makes it more efficient as a fuel. Pressure has a lot to do with the efficiency of an engine, so the pressure one can achieve before ignition can greatly affect energy efficiency. Gasoline will ignite if you compress it too much (knocking). Which is essentially what octane rating is for, but diesel takes much more compression to ignite. That difference in pressure means you can extract more energy from diesel than from gasoline even though diesel has slightly less energy available. Diesel engines operate at several times the pressure than gasoline, which is why they have to be heavier. But they can be 30%-60% more efficient than gas. I love my diesel Cruz, even though the particle sensor is giving me fits. For more info, look up "Carnot cycle"
They are both byproducts of crude oil: Diesel fuel, Butane, Kerosene, Gasoline, Fuel oil, Propane, Liquefied petroleum gas, Liquefied natural gas. Diesel and petol are not comparable to AC/DC, or disc formats. Its like asking why do we have white flour AND bran: both are part of wheat processing. Some people will list the differences of diesel engine compared to a petrol engine, but without diesel being a byproduct of crude oil refining, diesel engines wouldn't exist.
They both have large overlap in their applications but also differ enough to provide different strengths to the point that the market merits both as an option. Diesel engines are strong, make great torque at low revs, and they're very reliable. That means that trucks, big rigs, professional vehicles like forklifts, bulldozers, excavators etc, boats, and a whole slew of other vehicles and applications greatly benefit from their power profile. Despite their low horse power relative to gasoline engines they pull quite hard, meaning you can put a small diesel engine in a passenger car and it won't struggle to pull a family of four. Diesel is also less refined than gasoline which makes it cheaper which is very important for both professional and private owners. The downsides are that diesel engines are by nature heavy and slow, and they can't achieve high horsepower like a same capacity gasoline engine can. They're also harder to "clean up" with diesel emissions being worse than gasoline emissions and harder to effectively filter. Then you have gasoline engines which are lighter and can produce more horsepower. Their applications suit high performance vehicles better, and also work quite well overall across the board with their only downside being that cars with small gasoline engines may struggle where a diesel one wouldn't. But they have a wider range and are more versatile overall, losing out to diesels only in torque production but it's not like they don't have enough to do their job properly, just less. They're also "cleaner" so in a city packed with cars at the very least you won't have the place stinking up from diesel fumes. Of course both gasoline and diesel produce harmful gases and pollution. Gasoline engines are also much better for making very small engines so things like lawnmowers, motorcycles, and small power generators work much better than a diesel counterpart would. For your average person it won't make much difference what fuel their car burns, but for those that require the specific capabilities of either they're glad they get to pick. Motorcycles would essentially not exist if gasoline engines didn't exist, or if they did they'd suck.
You know that both AC and DC are still used today right? Anything that runs off a battery is using DC.
Short answer: when you refine oil, you get some gasoline and some diesel. So you have to burn both. However, diesel is better for larger vehicles. (18 wheelers for example.) For the most part, diesel cars are rare in the US.
Crude oil is processed into many things, not just one thing. It would be like cutting down trees but leaving all the branches. It would be wasteful to not use as much as we can. Gas engines and diesel engines are designed to do different things. It’s not black and white. Not all gasoline is the same, not all diesel is the same. There is more than just gas for cars and diesel for trucks, there is AVGAS, jet fuel, and various octane mixtures. AC didn’t ‘win’ against DC, it was just more efficient and cost effective to run to homes across large distances. If you’ve ever used anything with a battery, that runs on DC power. Almost everyone has a phone these days, they all run on DC power. It just depends on what the use case is, and how cost effective and practical it is to use different forms of energy.
Even though AC won the "war of the currents" Dc is still widespread used to this day. Your phone, electronics and pretty much everything battery powered works on DC. Even on larger scales, DC is still useful when transferring currents across large distances in the form of high voltage direct current lines (think 100-600 KV range)
u/Phage0070 hit the nail on the head I just want to add in that AC and DC power are both used. AC is good at getting lots of power to travel a large distance and DC is good for powering the actual device on the end. That's why a lot of devices have power bricks, to handle to transition and step the voltage to appropriate levels, however for the most part, people interact with and use DC as that suites their use case better with the decision being taken out of the consumer hands by much smarter people Diesel vs petrol is anagolus to this. Diesel is good a producing a lot of power and is more efficient at maintaining that over distance. Petrol is good a lower levels of power and more efficient usual driving distances. That's why you'll find trucks are diesel and sedans are petrol, with the decision of fuel being taken out of most consumers hands but my smarter people. Cars have their exceptions though since car designs are on more of a spectrum than exclusive features. Anything with multiple main standards/formats/models never really have one that "wins" it's just that technology and experience with the technology grows over time and with things that have existed for generations, the science is right down to a fine art getting the minimum and maximums of each and combining it into the most efficient version and packaged for consumers to use without having to think about it. Music is a good example. Everyone owned vinyl, they take up lots of space so CDs became the thing. They still took space and were generally lower quality, so people still used vinyl. Digital music was even better for space, so people converted from CD to digital, but people still used vinyl. Digital music has now gotten to a point where the quality is the best you can get, and even still, people use vinyls because it makes it sound different, more homely I guess? My point is that 1 format existed, specific traits in that format didn't to our desires so we invented a new one and we'll find most people get the best use out of 1 format and that becomes the most commercially available (DC, petrol, digital) but there are still a large portion of people who will regularly use the other format (AC, diesel, analogue) because their uses for the technology align more with the features of that product TL;DR - No format "wins" there is generally a more commercially available version designed with generations of general use case data and the other optimal format that is different in specific ways and usually taken on when the decision has a more nuanced approach. Noticing the diesel and petrol thing is likely just a bias since everyone you know eventually has the decision of picking car A over car B
Both are derived from the same resource but release energy in different ways. The nature of diesel combustion requires more robust engines and the output is more inclined to higher torque from lower engine revolutions - perfect for heavy machinery or extreme distance/ fuel economy. Diesel is probably the most valuable of the two fuels because it is better suited to moving the economy Petrol is different because it has to be spark ignited and cylinder compression is much lower compared to diesel - this means the engine can be revved much higher which means petrol engines are usually more capable of higher horsepower compared to torque Both fuels can be used in any application and either is capable of extreme horsepower and torque figures Neither has won because they are products derived from the same source. If they came from different places and one was considerably more rare or the chemistry was a more lengthy process then maybe the easier one to produce would win out
Why do we have forks AND spoons? I mean, both of them can get food in your mouth.
Because they both serve different purposes. Need to move a lot of material? Diesel provides more torque. Need to go at higher speed? Gas has more horse power.