5 Reasons Diesel Engines Make More Torque Than Gasoline
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- Опубликовано: 2 июн 2024
- Why Do Diesel Engines Make So Much Torque?
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If you compare gasoline and diesel models of the same vehicle, the diesel engine tends to have far more torque. Why is this? In this video we'll discuss the major differences between diesel and gasoline engines, that result in the diesel engine producing significantly more torque.
From the compression ratio, the speed of combustion, the bore vs stroke ratio, the use of turbocharging, and the energy density of diesel, there are many logical reasons why it's chosen for high torque applications.
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A question that keeps popping up is why don't any gasoline engines use compression ignition and higher compression ratios to be more like diesel engines. Well, Mazda is doing just that with their SkyActiv-X engine, and I've covered exactly how it works: ruclips.net/video/yNSxow3W7ek/видео.html
Hope everyone's having a great day, thanks for watching!
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Engineering Explained
Does that mean the new Mazda engines will have torque closer to that of a diesel?
Here may be a good question for a video: could you explain the differences/benefits between a V8 diesel and an I6, and how those engineering differences impact performance?
@Engineering Explained, You said that complete combustion of Diesel occurs sooner. But the longer carbon chain of diesel needs more time to burn than petrol which has a shorter length. I have some questions regarding this. Can you kindly spare some time in answering them please?
Mazda SkyActiv-X claims 20% more torque and horsepower while achieving 10% better fuel mileage, ive heard 10mpg improvment on all models.
It would be interesting to plot the torque over the entire 4-stroke cycle and show how this instaneous torque waveform (positive and negative) gets averaged-out by the rotational moment of inertia of the flywheel and combination of instantaneous torques from all the other cylinders.
Hey Jason. Im a wiever from lithuania. My girlfriend calls you the torque guy because she hears you say that alot. Love your videos.
Love it, thanks for watching!
All the best,
The torque guy
Where tf is lithuania
God Slave it's the place where lithium comes from ;)
Its a baltic state. Just above poland
lol u swapped the w and the v
I'm studying thermodynamics in college, first I watched an old video about the difference between gasoline and diesel engines, and somehow I ended up watching a tons of your vids. So interesting, love the way you explain everything!
A couple of things...if I remember my reading correctly, you have #2 backwards. It's gasoline that ignites (and burns out) almost immediately, the moment the spark plug fires. In a diesel however, fuel keeps getting injected until 20-30 degrees past Top Dead Center (TDC) on the power stroke, maintaining pressure for much longer. The reason this is important, is that when a piston is all the way up (at TDC) it produces little to no torque, the crank pointing straight up and being virtually in-line with the connecting rod. It's only when the crank has turned that the connecting rod can push against its side, creating torque. By that time, pressure in a gasoline engine has already dropped considerably, which is why you really have to hit the gas to tow anything with a gas-powered truck.
As for turbos, gas engines have their boost limited by the octane level of the fuel. As a gas engine compresses both gasoline vapors and air, too high a boost will result in detonation upon compression. In a diesel you're just compressing air, the fuel isn't injected until compression is complete. So, the only limit on turbo boost in a diesel is the strength of the engine itself--which is WHY they're built so strong.
Thanks for the comment. I don't have enough background to fully understand the first paragraph (sort of half get it) but the point about diesel turbos is clear even to me.
You do have a point.
I thought about this crank angle thing (because other people mentioned it too) for a while and I think a lot of people missunderstand how pressure works. If all the fuel is combusted immediately higher initial pressure will be created in the chamber. If the fuel is combusted slower then the chamber will start with a lower initial pressure but decrease slower because some of the fuel will be burning and counteracting that pressure loss. If as you say it would be best for the fuel to burn at the best crank-lever angle then gasolines engines would fire the spark plug then, which they dont do, most even advance the timing of the ignition before TDC.
Gasoline has a flame front, a spark plug initiates the flame which travels.
The diesel burns everywhere at once because there’s no one single point where it has to start.
I saw a diesel drag pickup running 140 lbs of boost. 140!
This channel taught me more that all of my years in school and college, thanks legend❤️
Some people are natural teachers and love to impart their knowledge. Too bad in most countries teachers salaries are so bad, otherwise more people with the actual calling and ability would take a teaching job
@@svarthofde2492 it's not only salary, many of them can't do what they would want to because education is very strict and systematical, they're getting fired and getting harassment in their address, basically a dead system that still exists, ignorant parents who only care about their children graduation and grades and not their knowledge doesn't help either
That doesn't reflect well on you, I must say 🤣
Maybe you were not curious or inquisitive and just expected to be spoon fed everything.
You either got a bad school or didn't studied enough.
Your post is a standard text in many yt channels...didnt school teach you to be original ?
One of the few channels ran by a youth who's able to properly explain the automotive world in detail! I'm a mechanical engineer too and this is how these kind of topics should be explained!
Too easy to test drive expensive cars only because you have a lot of money and saying things that everyone would be able to notice only by reading a brochure.
As always can't wait for the next video! Thanks Jason \m/
Perfectly put 👍
P
Channel ran by a 'youth'....a few weeks ago, this guy said he was born in 1953...so he's 65, certainly surprised me...!
he's from 1963
Steam engines- "Hold my beer."
loke yeah they make 25hp but can go to speeds of up to 200mph
Steam tractors:
Horsepower: 150
Cylinders: 1
Torque: Enough to move the world
Also external combustion, not internal
@@renz1013 no steam engine that makes 25 is going to make anything go 200mph
@@chaztitan6457 No Steam Engine ever went significantly beyond 200 km/h (125 MPH), and these had about 2500 kW (3400 HP)
Jason, great video. But I have a different take. Diesel fuel is an "oil" and burns SLOWER than gas. This is why diesels cannot create much horsepower; beyond about 4000 rpm the diesel piston is literally "running away from" the expansion of a slower combustion rate. But because diesel burns SLOWER, combustion reaches peak expansion LATER -- when the piston is LOWER in the cylinder. In your video on "torque vs. horsepower" you do a good job of explaining that Torque = Force X Lever Length. At Top Dead Center and Bottom Dead Center the effective "lever length" of the engine crank is ZERO. So during combustion, lever length (torque potential) starts at zero, rises to maximum as the crank turns and the lever length increases, then falls back to zero. In a "standard" gas engine (normally aspirated, square bore, decent compression ratio) peak combustion pressure is reached at ONLY 15 DEGREES OF CRANK ROTATION (midway between 1 and 2 o'clock, on a clock.) This is because gas burns quickly. But at 15 degrees "lever length" is VERY short. Torque is minimal even though combustion pressure is highest at this point. As the piston descends cylinder pressure DECREASES (because volume INCREASES.) That "typical" gas engine has its best "mechanical" torque potential at 72 degrees of crank rotation (which added to 18 degrees of conrod angle = 90 degrees. Best torque is created by pushing on the lever at 90 degrees.) But that "standard" gas engine develops peak torque at ONLY 42 DEGREES of crank rotation, because this is the best intersection of rising mechanical (torque) advantage and decreasing combustion pressure. After 42 degrees, combustion pressure drops so rapidly there's too little pressure to take advantage of the better mechanical advantage that exists at 72 degrees (the "longer lever" moment.) But because diesel burns slower, it reaches peak combustion pressure when the piston is at a LOWER point in the cylinder, where there is a greater mechanical (torque) advantage. So, diesels create higher torque, but produce very little horsepower because diesel burns too slow to keep pushing the piston faster and faster. (And this is why the torque/horsepower curves of a diesel engine "cross" at much lower rpm than gas engines.) Gasoline burns so much faster, it can "push" an engine to higher rpm, and since (as in your "torque/horsepower" video) power is the SPEED at which work is accomplished, gas engines develop higher horsepower. But less torque because they create peak combustion pressure at a less advantageous (earlier) crank angle than diesels. However, since gas engines can rev faster, they can generate more of these "peak moments" per revolution of the vehicle's wheel. So they accelerate faster, have a wider useful rpm band, and don't need as many gears to move a vehicle to a high top speed. Incidentally, the difference in "burn speed" between gas and diesel sheds light on why a super/turbocharged engine develops more power. Not only does it raise the temperature (higher thermal energy) it raises the compression ratio. Higher compression ratios cause the burn to take LONGER to complete. Meaning there is higher combustion pressure when the piston is lower in the cylinder, where there is more mechanical (torque) advantage. This is a big part of the reason why super/turbocharging either a diesel or gas engine increases its power. Sorry for the long comment. Hope this is useful...
Impressive and understandable explanation!👏👏👏👍🍻
I'm on board with this, the diesel is getting much of it's torque from the stroke length and good for you for pointing out that with the slower burn that there is most certainly a HP limit. Just another note diesels were not always turbocharged. Although sure your getting some torque increase from turbo charging diesels they really put turbo's on to get the HP up there, e.g spin them faster. A current CAT bulldozer is still turbo because why not take the extra torque but they were looking for the HP as that means you push more dirt around in a given time. Same for hauling freight on the highway, increase the HP and you can pull the load faster and get paid more. If you drive a diesel often, you will notice they mostly never "lug". They always have extra torque on hand.
I agreed with everything in your comment right up to the point where you said that higher compression slows the burn rate. I'm sure that is not true. In fact, in a gasoline (or any spark fired fuel) engine it increases the speed of the burn. This is why higher compression is necessary for extremely high rpm engines. With lower compression the burn rate hits its max at a lower rpm and will not push the piston faster. To make an engine that will run at 8000 rpm you must increase both air flow AND compression.
With diesel, turbocharging increases cylinder pressure, increases the amount of oxygen in the cylinder, and allows the injection of a lot more fuel. It's the additional fuel that creates more torque.
I agree that higher pressure when the piston is lower in the cylinder is giving the high compression engine more power. But the piston must be moving a lot faster too for this to work.
@@michaelcooley8275 You're totally correct, higher compression doesn't slow the burn rate. A volatile gas expands FURTHER when it explodes if it has been compressed more before combustion. So it takes longer to reach full expansion which means there is more combustion force when piston is lower in the cylinder, where the torque from a superior crank angle is better. If I said the burn rate is slower I spoke incorrectly. Good catch.
That's def also part of it. Its several different things put together really
I don't know if you've mentioned this in other videos, but the implications of piston speed: A higher piston linear speed means that the peak force experienced by the connecting rod will be higher and thus the connecting rod must be stronger in order to withstand this force. (This also applies to the wrist pin, the piston itself, the crankshaft etc)
Jason, love your videos and I really appreciate your ability to convey complex topics in a way that mere mortals can understand.
Thanks for answering a question I always wanted to ask, but could never find anyone to properly answer. That has always befuddled me about diesels, and their amazing way of producing gobs of torque.
I always wondered this, I had a vague idea but you explained all perfectly and resolved all my doubts. One of the best content creators here, keep up your great work man! Cheers from a proud Diesel owner in Argentina!
There were a couple of questions in my mind about Diesel engines, but after watching this video, everything is clear. Thank You.
Hands down the best RUclips channel for so many reasons.
Jason could probs do the maths to prove it.
This was a very satisfying video sir, u never stop making one of the best auto explanation videos ever. Keep it up ur awesome work.👊🏼👊🏼
I admire people who are able to explain technical things so well! Thank you!
Great video as usual! I would argue that in a Diesel engine complete combustion does not always occur right away.
You make it sound as if the fuel is injected in a quick shot and bam, it’s all instantly burned up just after TDC.
The duration of injection or number of separate injection events per power stroke depend on the amount of fuel needed to be injected which is primarily determined by engine load. At idle a small quick shot of fuel may be all that is needed to keep everyone happy, but obviously when pulling 40 tons over a mountain the engine will require a lot more fuel. What I was taught is that one of the beautiful things about a Diesel engine, and one of its main torque producing characteristics, is that it can continue to inject fuel and burn it throughout the entire power stroke. In convention gasoline engines a given amount of fuel and air is drawn into the cylinder in response to a given load, what’s taken in is what you get and as it burns during the power stroke the amount of downward force drops off as the fuel is used up. A diesel is capable of continuing to inject fuel throughout the stroke and will therefore maintain the downward push the whole way down, equaling more torque.
Take a look at how a normal inline injection pump meters fuel with its port and helix set up. At light load there is only a small amount of the helix exposed which means that a small amount of fuel will be injected, but the plunger will still make a full stroke, so it would still be injecting fuel during the power stroke if it had been given it. As load increases more fuel is metered in and then injected, not all at once, but throughout the power stroke.
I came here to say this.
This is called the “Cutoff Ratio” and has become electronically controlled in common rail diesels. The classic diesel thermodynamic cycle maintains constant cylinder pressure throughout the power stroke, achieved in practice by continuing to burn fuel as the piston descends and the volume increases. This means that a diesel piston is still being pushed down with the same force when its (longer) crank arm is at 90 degrees. THAT’s where the stump-pulling torque originates.
(Great channel.)
Also: common rail systems can control the rate of fuel delivery by modulating the rail pressure, so the fuel dose can be delivered quickly at high rpm and high load, or drizzled more slowly at lower load or rpm.
My CDI’s rail pressure varies from 4500psi at idle to >22,000psi at full load.
By electronically varying the timing and duration of the injection event for a given fuel dose the engine module has good control.
Fuel is injected at extremely high pressure, so it'll burn quickly and glow plugs may help
I’m doin me a good ol learn
that'll learn ya
Very informative vid. Thanks again for another great vid. These are great! 👍🏼
Also, diggin’ the new adding of animation..score! 😁
Man do I love your way of simplifying complex concepts.
Excellent use of graphics and videos 👍🏻👍🏻
Excellent lecture, thank you. Makes me sad that I’m giving up my 6MT TDI Golf and have decided on the gas-driven NC Miata for cruising. I’d love a way to replicate that low-torque push for an MX-5 and get real efficiency. Diesels are awesome for so many driving use cases.
I love your videos man. I’ve never fully understood the engineering behind diesel motors. This video explained a lot for me. Thanks
I love seeing your videos. You do great job of explaining with great illustrations. Please keep up with your great works.
Thanks!
Great succinct and informational video Jason!
I was just thinking in these past few days whether you ever made a vid on this exact issue. Question answered. Superb video. I enjoy all of them very much.
Another one of my life questions answered! Keep 'em coming! I love your videos!
Man thank you for all of your videos. I have learned SO much from them. I try to watch them all when my Exede internet is not about maxed out. I hate satellite internet. Your videos are explained in a way that I understand easily when compared to other engineering channels I watch.
Very interesting videos, thank you for taking the time to create and upload them.
Absolutely beautifully executed. Bravo! Definitely liked. Already subscribed ;)
Diesel engines are great, it’s a shame they’re being killed off.😢
Yeah, the petrol companies love inefficient engines. They require you to visit the pump more often.
@@Kit_Bear What a poor attempt to label oil companies as the problem. Environmentalists are the ones pushing against anything that burns hydrocarbon fuels.
@@haliax8149 So you are a polluter-friendly turd!
Environmentalists killed the diesel
@@stmounts No. Where exactly does it say "I love pollution" in my statement regarding diesels? Carbon recycling systems seem to be the best option from what I've learned. C02 and water with thermal input being used to produce commodities like methyl alcohol to power existing vehicles.
Thank you for making diesel videos! Looking forward for more diesel content, especially on how to improve performance on diesel engines.
I always learn new stuff from you. Thank you! I usually have to update my knowledge about engines so I like watching this vids!
Very nice video. The way you explain things is just amazing. I am 19 year old kid who is about to join college. And I am incredibly passionate about cars and engines thats why I watch your videos.....
That can't be true! The media says the younger generation only cares about cell phones and public busses! :)
volvo09 I DON'T KNOW WHICH SURVEY YOU ARE TALKING ABOUT BUT WHAT I KNOW IS I LOVE ONLY CARS!!
volvo09 he his watching this in a phone ahahahah
passion is always the best teacher. Just go for it if you like it.
Liucu Liu cannot agree more!
Well explained as always. Thanks.
Stunning explanation. Thanks for your time and solving that problem for me. Just subscribed. Cheers. Jon.
I always enjoy your informative vids, this one was particularly instructive.
Very well done video, my hat is off to you sir, thank you
Hey man, congrats on your great show, really enjoy learning from it. I was wondering if you could do a vid explaining what are rpms, and the fuction they do on ones vehicle. Would really appreciate if you did this, man. Thanks!
Some time ago I was asked about interesting and useful channel on RUclips. Well, I gave EngineeringExplained as an example. Good job!
You always explain in a simple way that I can understand. I appreciate all your videos, thank you.
i appreciate how simple to understand, remember & share your knowledge, thanks for being so dang smart..
The true reason most diesels make more BMEP is as follows:
1) They do not suffer from detonation or pre-ignition, meaning an ultimately higher Cylinder pressure and temperature is possible. (a gasoline engine would need to be run on a very high octaine fuel to produce the same BMWP without damaging abnormal combustion events)
2) Compression ratio. An engine is a thermal device, ultimate efficiency depends on compression ratio. Higher CR = more BMEP
3) Average cylinder surface area during combustion. Again, DI engines burn their fuel at lower average combustion chamber volumes and hence lose less heat to the chamber walls. More heat = more pressure = more BMEP
In all cases the charge burn angle is calibrated to position the peak pressure point at a geometrically optimum point in the stroke. For most engines (typical geometries), this is around 10 to 15 degCA ATDC. In a SI engine this is done by optimising the ignition angle (where the spark occurs) and for a DI engine by optimising the injection angle and injection mass profile.
Modern DI gasoline engines are now actually pretty close to diesel engines in terms of maximum BMEP, but can produce significantly more ultimate power as they don't suffer from the same burn rate limitation as a diesel that limits the practical speed for peak power to around 5krpm
When they used Diesel engines in LeMans racing (Audi and Peugeot) even these racing engines have the max power around 5000 Rpm.
And the reason is exactly you stated that the burn velosity restricts higher RPM.
A follow up video would be nice, since I think there is some confusion here.
I actually did some combustion development and port optimisation for the Audi R10 TDI LeMans engine, and ultimate burn rate was the power limiter that drove the engine design towards a high BMEP, low speed, low friction type architecture! Add in the mandatory air restrictor and it was always going to be a engine dominated by it's combustion efficiency rather than combustion power!
Amazing comment better than the video ! How are the new gasoline engines get torque as a diesel counterpart, but more power and they have quite good economy too ?
Well that's a amazing coincidence that i choose to mention the LeMans diesel :)
Spoken from a true garage tuner !
Awesome! I just asked my DJ to get a diesel-turntable to gain more BPM!
I really enjoy your explanatory videos on mechanical engineering. All of them are very well explained.... please, keep posting
Great video. Thanks for putting it together. Very informative.
Hi Jason - Nice video. It would be interesting if you could do a segment (if you have not already) on how engine designers create an engine for more or less torque, along with how they control what RPM that torque reaches its peak. Obviously your video touched on some aspects of what influences torque; it would be interesting to list all the variables and their trade-offs versus each other. Thanks.
Well, there is actually only one reason that diesel engine is PERMITTED to have more torque than gas engine, and that is because diesel engine is built much tougher than a gas engine in order to handle more torque. Diesel engine has a slower combustion process therefore cannot produce torque at high speeds, so to make up for this, it must have higher torque at lower rpm to compensate for the lack of torque at higher rpm. Gas engine is designed to be light, plus risk of detonation at lower speeds with higher loads, therefore is NOT permitted to have high torque at slower speeds, because it will self-destruct. At higher rpm, gas engine cannot complete its combustion until the piston is halfway down, therefore cannot impart all of its combustion energy to the piston, so its peak torque is lower than that of the diesel engine that is ALLOWED to burn more fuel at lower speeds due to the lack of detonation risk, but that's by design only. Theoretically, a diesel and a gas engine burning the same quantity of fuel per stroke at low rpm at which complete combustion happens early in the piston downward stroke should have similar torque...but of course, in real life, the gas engine is NOT allowed to have its peak torque due to its lighter construction and the risk of detonation at lower speeds with higher loads.
Excellent video explained in such a way even I could understand it. Bravo!!!
Happy to hear it, thanks!
your videos are brilliant. When ever i explain stuff to my kids i always use your videos and they get it every time.
Thanks for clearing this up for me. Very easy to understand.
I appreciate a lot your work: it's great, keep going!
Unfortunately I have to say something about the topic of this video:
First of all It's true that Diesel engines have higher compression ratios resulting in higher Peak firing Pressures and consequently higher values of torque BUT this is not the "true reason" why CI engines have more torque COMPARED to SI ones.
In fact, while the SI engine works always stoichiometric (or even slightly in the rich side (relative A/R (Air Fuel ratio) ~0.9)), the Diesel engine cannot work anywhere close to the stoichiometric A/R due to t bad air utilization (min relative A/R is in the order of 1.2-1.3) thus resulting in ~20% less fuel injected (in mass) for the same quantity of air in the cylinder. Lower fuel injected means lower energy released in the combustion and so lower torque (this "base" 20% deficit is partially, but non totally, compensated by the higher compression ratio and higher Diesel specific energy). If you compare the torque figures of old naturally aspirated diesels with NA SI engines of the same time you'll verify what I'm saying.
The second thing you mentioned is not wrong but it's not that relevant: the combustion of a Diesel engine is more efficient when it tends to a constant-volume combustion (like in the case of the IDEAL Otto cycle).
For partial loads, the actual duration of the two combustion processes, even if they're fundamentally different, is comparable and I would say that there are so many variables involved (speed, temperature, fuel quality, turbulence in the clinder, etc) that is difficult to say which combustion process is the most efficient.
However, at high loads, the combustion process of a SI engine is definetly occurring faster than a CI one since the latter has to fight against a "mixing controlled combustion" during which fuels struggles to find air to react with. (In fact, CI engines rotate slower than SI ones)
For what concerns the third point you presented... it's just a false myth: the higher lever of a longer stroke is counteracted by the lower force resulting from a smaller bore. If you take the condensed formula to compute engine power you'll notice that bore and stroke are multyplied together giving as a result the displacement (longer stroke -> smaller bore).
So, the reason why diesel engines have much higher specific torque than SI ones is turbocharging.
Thanks to the very high allowed boost ratio it is possible to force a lot of air inside the cylinder and so it is possible to burn more diesel than gasoline (for a given displacement). This results in a much higher torque together with a more efficient engine. (Power output, unfortunately, si affected by the "slow" combustion process that doesn't allow the engine to rotate as fast as a SI engines).
This comment doesn't want to be against you.
You've always done a great job. It's just to make things a little bit clearer.
Appreciate the feedback, thanks for sharing your insight!
Diesels also have much stronger internals resulting in more spinning mass within the engine which helps with torque. If you lighten the internals in a gasoline engine, you'll gain power but at the sacrifice of torque.
Jason I'm your fan but that was not the best movie you did. Federico pointed out why in very good and informative post above. Remeber your movies are also wached (with pleasure!) by professionals. :-)
I'm curious about one of your last statements.
"Power output, unfortunately, is affected by the "slow" combustion process that doesn't allow the engine to rotate as fast as a SI engines)."
My question is, doesn't the combustion process happens quicker on a Ci engine than in a SI engine?
As was explained in the video, (or how i think it was, and how i have interpreted) the burning process of a diesel engine happens in slightly faster instant than petrol.
And another question, when comparing both CI and SI as turbocharged engines, is it expected to the SI engine have more torque (and?) horsepower?
Thank you in advance if you answer! :)
In SI engine fuel is injected during intake stroke. It has time during intake stroke and then majority of compression stroke to vaporate and form proper A/F mixture. There is no such a time in diesel. In diesel fuel burns once its injected but injection itself takes some time thus crank angle rotation. Moreover at high loads mixture is too reach right at the injector nozzles and it needs some time to mix with air to burn. Thats why you see black smoke in diesels under load. They don't fully burn fuel. All in all diesel combustion takes longer then gas at high loads.
I always learn a lot from you videos. Thanks for posting! I even have my wife watching some of them with me.
Happy to hear it, thank you both for watching!
Engineering Explained
Haha watching your vids is like hanging out and listening to my dad talk engineering. just you’re 40 years younger 😬
Another informative video. Nice work!
Awesome explanation! I love your animations!
LOVE IT!!! Thank you for the killer, straight to the point vid with some GREAT visual aides!!
I'm sure this was not quick and easy to put together!! (well, at least not QUICK...most likely quite easy for that brain of yours my friend!!) :-)
If you do the calculations, you will find that bore and stroke does not effect torque, when cylinder pressure and displacement are equal. The idea that it will is a very common misconception since it is easy to see how a longer stroke might increase torque, yet less obvious that a larger piston will likewise increase torque.
Yeah, if you are looking at *work cylinder-wise*. In fact the crankshaft of a long-stroke engine acts as a reductor, producing lower speed and higher torque.
Great Explanation! Thank You!
Great videos keep them coming.
I was always taught and read that diesel combustion took longer than gas. Some of the combustion occurs in the power stroke. Otto vs Diesel cycle
Doesn't take as long, but you can (if you want to make more power) continue to inject fuel during the combustion stroke with diesels. Not efficient, but you'll make more power and it will appear to burn longer (though really it's just a continuation of fuel injection).
This is what I was taught by instructors while taking diesel technology courses. The torque output has a direct correlation to fuel timing. Because of the slow burning nature of diesel fuel, during the power stroke it can be injected into the cylinder after top dead center.
That's true which is another reason it's more suitable to a long stroke low revving engine to take full advantage of it and the fact that diesel fuel has more like 30% more energy per gallon than gasoline, not 15% as he stated.
You touched on all the right points, however, Diesel engines do not burn evenly nor completely as you stated, the combustion in a Diesel is a Heterogeneous one , when fuel is injected, the outer part of the spray burns lean while the inner does not and takes longer to combust, secondly I expected you to expound more on the importance of no throttle body in a diesel, rather than generalizing it as pumping losses, the more technically correct term would be Higher Volumetric effiency as a result of no throttle body
And who cares about heterogenous burn? That's why diesel engines are made sturdier.
Fantastic basic explanation. Thank you
Great video as always!
It's good thing. I knew about diesels for so many years. Been driving diesels since I was a kid.
I still drive gas and diesel! 6.6 liter V8 Duramax and 5.7 Vortec gas. Lol
Look at the Nissan Patrol from the 90's. They have a 4.2L naturally aspirated diesel (TD42) and a 4.2L naturally aspirated petrol engine (TB42). The bore and stroke are identical on both, yet the petrol produces 15% more torque and 30% more power at only 200 rpm more. I realise this is a one off but it's a great comparison of engines with identical bottom ends which eliminates the bore and stroke argument.
Reason why dragster snatches 6.2 Chevy diesel engine blocks and throw on gas heads and use electronic ignition because the blocks are the same there just beefier! then supercharge it or turbocharge it and crank up the boost!
Your math is wrong. You were supposed to compare torque/fuel, not torque/engine_configuration
TB42 is a fuel monster, while TD42 consumption is decent for its performance.
Awesome introduction! thanks for the clarification.
I see that you made some workout since the last year ! Results are showing up ! Keep going with your videos, I really appreciate them
Btw I'm a viewer from France, you are becoming an "international car engineering explainer"
The stroke length is very important for more torque and your illustration shows it quite clearly. In order to have a longer stroke, the crankshaft has to have a larger offset to the connecting rod in order to move the longer piston stroke. That larger distance means that the piston is in effect pushing the crankshaft around using more leverage. It's like using a longer wrench to loosen a stuck bolt. The larger offset the crankshaft has is like the longer wrench.
USWaterRockets But.... If you keep the same capacity of the cylinder then longer stroke means smaller bore and piston area thus force pushing piston down. All equalizes. ZERO effect on torqe. Jason simplified it too much imho.
Sewer Razus
Correct. Longer stroke with smaller bore means lower stress of the components, provided RPM is not too high.
Since area is dimension squared, halving bore diameter means quadrupling stroke length to get the same displacement. Force on the piston is area times pressure, area is one quarter so it's quarter the force. Torque on the shaft is force times crank length, so that's quarter the force and quadruple the length. All comes back zero. And why wouldn't it? The compressed combustion products make certain amount of mechanical work by expanding to certain volume. This means this amount of mechanical work will go to the shaft, no matter the bore and stroke configuration.
Mi 28 +1, I was very surprised Jason was so confused when he spoke about it
The thing he missed is that the diesel injection and so its burn duration is longer, so the cylinder pressure is held constant as the piston descends. This means the combustion pressure is still at its maximum when the crank is swinging past the 90’ and the piston has its best leverage. A gasoline engine has lost a significant amount of pressure by the time the crank swings through 90 degrees, so the piston isn’t generating the same torque.
It doesn't matter, power in = power out. You can't bypass thermodynamics by jumping through hoops in specific order.
Yesterday i wanted to search engineeringexplained video of this but forgot, now i'm remembered....
Excellent explained!
Earned a sub and like from me. I've watched several of your videos and you are so good at explaining everything and breaking it down for mechanical idiots like me! Keep it up man!
Please make a video of gasoline versus ethanol. How does a full flex fuel engine performs with each one of these fuels?
complex topic. Would be interesting but this is closer to chemistry than engineering. :) A simplified answer from me (not an expert) would be ethanol has less energy than gasoline but burns hotter and faster (cleaner) allowing for you to pump more in at a time to make up for the energy loss. High ethanol fuels can overheat an engine or burn out seals on an engine not made for it.
Unless technology has changed -- which is very probable -- it used to take 1 gallon of gasoline to produce 1 gallon of ethanol so it was more of a waste of time for anything other than performance engines like F1 or NASCAR vehicles.
acephantom903 I live in Brazil and here we have flex fuel engines for over 30 years. Nowadays more than 90% of veihcles sold each year here are flex ones. Almost every gas station here has pure ethanol (94% actually) pumps. Most flex engines here can produce more torq and power from ethanol than gasoline. In many parts here is cheaper to run on ethanol than in gasoline.
That is interesting. I wonder how you have ethanol so cheap. Maybe it isn't that the ethanol is cheap but the cost to import gasoline is high? Flex fuel engines are made to handle to increased heat while normal gasoline engines can handle a max of 20% ethanol before it gets dangerous. Because you have such high ethanol contents, your car's computer can see that and can increase fuel injection to give you stronger power than gasoline as it doesn't need as much air while combusting. Do your flex fuel vehicles also have a setting to increase fuel efficiency when running high ethanol rather than higher power? It would only be a computer setting change to have the different modes.
Fernando Sousa ... iirc...it takes 30% more ethanol to get the same energy output of gas. Ethanol also is higher octane so lots of turbo guys like it for high boost.
Fernando Sousa
I had a Brazilian classmate in tech school some 20 odd years ago, and that’s about what he said.
Gasoline is for washing parts 😂
You are so young and know Soo much about engines . I like your videos
You're probably the first person calling him young on the internet, I bet he would shed a tear of happiness if he read that
Best channel for brainy petrolheads! Awesome job simplifying complex topics. Amazing job as well incorporating the live examples at the right time for a smooth overall explanation!
Interesting, I always thought Diesel burned slower than gasoline, I did know about most of the stuff other than that, but as always, a new surprise awaits every time you review some known topic. Great explanations as always, you always set expectations quite high on your videos, and deliver the expected. Keep it up!
By the way I finally started watching these on my 4K tv, I can finally read the whiteboard
one of the best youtube teacher .....lots of love from india....
Hema Kumar i wouldn't say one of the best but he surtainly is does the job ;D.
great video, very informative and comprehensive
Well done! Thank you for explonation !
But gasoline engines run on the Otto cycle which has a constant volume heat addition straight line on the graph. This represents gasoline burns much faster than diesel. And diesel cycle has constant pressure heat addition.
Diesel does burn SLOWER than gasoline, that's why they can't rev that high...
NA diesel does not have more torque than a NA gasoline. The higher CR AND turbo (and multijet) gives higher torque. Turbocharge a gasoline and torque is there as well. Diesel efficience is higher due to higher CR (higher thermal efficienty) and higher BTU/volume compared to gasoline.
You are aware that you are contradicting everything he says in this video? Diesels can't rev that high due to longer strokes and higher piston speeds relative to rpm and diesel fuel burns quicker in an engine, almost instantaneous as it uses the heat created under much higher compression. @@ivojanssens221
@@Leemur2335 no way! Diesel engine sounds like the chain of many explosions but gasoline one doesn't. Just think, why? The answer's simple - combustion at diesel engine is the fast explosion. Not the same, and gasoline combustion flows very slowly in one cycle.
Thank you for explaining this. I've always wondered why diesel is stronger than a gas engine.
Part of diesel efficiency is its lack of a throttle body. It always fills the cylinder with air, it varies the power output by varying how much fuel is injected. If you’ve seen a truck with just a hint of black smoke under load, they are running about as powerful as they can without wasted fuel.
Its because turbocharging...Naturally aspirated diesels have much less torque and power than gasoline engine in same displacement.
Same displacement, gasoline engine more power. Equal power, diesel more torque.
Yes, more torque but only in crank, diesels have smaller usable rpm, then they have much taller gears to achieve same vehicle speed.
I’m sorry to say he did not explain it. He was also wrong regarding literally almost every reason he gave. There is one reason: Diesel engines don’t have to worry about knock and or pre-ignition at low engine speed like gasoline engines do. You know how on modern turbo gas engines how the middle part of the torque chart is flat? That’s a limitation to avoid knock. High pressure, high temperature, and ample time mean that the combustion would not proceed as desired if the boost pressure wasn’t reigned in.
Excellent video, perfectly presented, clear, concise.
Well explained and illustrated.
Bore / Stroke doesn't affect the torque - Consider 2 engines have the same volume and pressure. One has 2times the stroke but only half the piston area. You get 2 times the distance and half the force.
No, you will get more torque because of the longer arm of the crankshaft. But you'll get less horsepower because it can't rev as high as the short stroke engine.
Bravo, at least somebody understands physics and mechanics. Most of the posts and comments on here are just wrong, and the frightening thing is that people with no technical insight blindly accept it.
Yeah, but in fact the crankshaft of a long-stroke engine acts as a reductor, producing lower speed and higher torque.
Erm, probably the most important part would be the turbo on the side. A non turbo diesel (aka NA diesel) has very little torque compared to equal sized petrol engine. So obviously it is the turbo. Sure, a turbocharged petrol will not make as much torque as a diesel from factory, but then it has the rpm benefit. A 2.4l 6 cylinder diesel with no turbo makes less torque than an 8V 2.3l 4 cylinder.
Volvo fan? ;)
szafirowy01 yeah... B230F vs. D24 :D But I changed brands about 3 years ago... Now it is Jaaaaaaaaaag :D
Mmm, similar to what I like ;)
Nathaniel Vas try the BW 1.9 SSI. A TDI without the turbo. Otherwise direct injected. Still makes less torque.
Appreciate your work !
Cleared my doubts. Well explained sir. Ty
Do not agree with your suggestion that diesel has a faster speed of combustion. In fact diesel fuel burns more slowly in the engine because it is being sprayed into the cylinder with the injector over a considerable portion of the piston down stroke. In fact the ideal is to produce a constant cylinder pressure as the piston descends and this is the main reason diesels have higher torque. With a gasoline engine the spark determines almost instantaneous combustion with very rapid flame progression at the top of the piston stroke and the pressure falls off rapidly with the piston descending. Clearly this will produce lower torque. Dan Hanlon.
This is true. This is also the main reason why diesel engines can't rev past a certain point. Depending on stroke length, the theoretical limit can be anywhere between 5.5 and 7000 rpm. For most engines, it is around 6000 rpm. If you exceed this limit, you will still have considerable expansion when the piston hits BDC, grenading the engine.
Diesel burns MUCH slower than gasoline, which helps it push on the piston for a longer period, taking advantage of the longer stroke... That, is why they have more torque.
It does burn slower, but that doesn't translate into producing more torque.
Let me know if you would like a more detailed explanation.
Brady Black I'm not the original commenter but I'd like a detailed explanation
Of course! To put in layman's terms, when you combust fuel past top dead center you are effectively reducing the amount of possible work you can get out of it. Fuel that has been burned at the beginning of the the power stroke will have more of its energy extracted out as work (torque). This is mildly similar to how a higher compression ratio will result in more power output. Injecting fuel late (and therefore igniting late because we are talking about a diesel engine) is reducing the amount of work the fuel could have done. Obviously this is inevitable because diesel engines can't inject fuel instantaneously, but it is in no way beneficial.
Does that make sense?
Brady Black Makes perfect sense. If you ignite the fuel when the fuel is compressed to as small space as possible (TDC) it gives more powerful expansion compared to igniting later when it would produce less force
Kinda. So the pressure IS higher (I think thats what you mean by a more powerful expansion), but it is also that the force exerted on the piston is being over more time (more crank angle degrees).
Amazing explanation - thank you!
Thanks so much! I searched for why semi trucks run on diesel engines and your video was the only one that could explain it properly.
Jason, stroke does not have a direct impact on Torque. Toque is a function of mean effictive pressure and displacement. For the the same displacment, the longer stoke engine would have a longer moment arm but the area will be lower, thus resulting in a lower force acting on the piston for the same efftive pressure.
Agree totally :-)
That may be true of normally aspirated engines burning the same fuel at the same compression ratio. You act like a longer stroke engine necessarily will have a corresponding smaller bore and vice versa. Forget displacement because it doesn't mean the same thing when you compare a diesel engine to a gasoline engine. A short stroke gasoline engine might make the same peak torque as a long stroker of the same swept volume but it will make it at a much higher RPM which isn't conducive to getting a load rolling from a stop or for engine longevity. The diesel is not going to have the same pressure as a gasser, it will have more because the fuel is more energy dense and it's operating at a higher compression ratio, another reason the diesel engine has to be built stronger. GM tried to convert a gas engine to diesel and it was a total failure because it wasn't strong enough to handle the higher pressure and torque created by burning diesel.
All that being said I think what he really means is the longer stroke does mean more leverage turning the crank at lower RPM which is the definition of a 'torquey' engine.
This doesn't seem to jive with the labeling of a spark-ignition Otto cycle as a constant volume expansion where cylinder pressure drops during power stroke versus Diesel cycle labeled as a constant pressure expansion. Constant pressure suggests combustion is occurring and fuel is being supplied during a significant portion of the power (expansion) stroke. This in turn suggests slow burning in Diesel and a controlled explosion in Otto. Please elaborate?
see above comment reply
The post contradicts ur nomenclature. This post states that diesels complete combustion sooner than the gas version. What further elaboration is needed?
The explantation regarding the false logic provided. Diesel does not complete combustion sooner, look at basic thermodynamic p-v plots of otto and diesel cycles.
Reiterating a statement from a posted vid is not an explanation and has nothing to do with logic. false logic... lol
Have fun getting him to look at ur basic or non basic thermodynamic p-v plots, thats outside my purview.
I was simply referring to the false logic provided in the video. There is no problem if this is outside your scope of understanding, but I find it unfair for you to criticize his request for an elaboration. His question was valid, and you told him to rewatch the video.
Beautifully explained.
This video has clarified some points to me. Good explanation 👏👏👏
Love your channel man. I'm not an engineer, but I'm a good mechanic and great MX/Snowmobile rider. Everytime me n my buddies get into an argument over something, I pull up one of your vids. So thanks for helping me win drunken arguments! Lol
I love my 520D ❤️
amazing car, amazing engine
What about 525D :D
Jerrypintoswe drive and 530d and get back here..
Bharath M of course its faster. Still love my 520D
Bharath M or 535d
I love your shows. You explain your topics so well. Pete 🇬🇧
Thank you for these excellent videos. Wish I would have discovered you sooner!
Take a gasoline enginge and a diesel engine same bore and stroke and same displacement and you will find out that the gas engine makes more torque.
If you mean both with the bore and stroke of the gas ones, yes. If with an arbitrary bore/stroke, no.
You can't because of octan's flash point. Over 12 Cr, gas engine starts knocking...
Diesel engines make way less torque compared to equivalent (same era, same displacement and same boost) gasoline engines.
For example, 2004 Golf V 2.0 SDI makes 140Nm while 2.0 FSI makes 200Nm
Or 1994 Merc C 2.0 D makes 140Nm while 2.0 G makes 190Nm
This is the reason that NA diesel engines have disappeared and turbo is a must.
The only common "torque advantage" of the diesel is the lower rpm range.
Also longer stroke for same displacement does not increase torque because greater leverage compansates greater force for the same pressure
Actually the only true advantage diesel engines have, is efficiency.
Any car maker can produce a gasoline engine cheaper, more reliable and with a better torque curve over the entire rpm range from the same displacement, than any given diesel engine. but can't even get close to the diesel efficiency. As simple as that.
I agree Diesel engines are good for efficiency, I also think diesel is good for longevity, but with all the emissions killing and cooking Diesel engines it's not worth having one anymore,plus the price of a Diesel engine upgrade ,,, and the manufacturers got people tricked into thinking 300k is a lot of miles for a diesel , so many post on you tube people bragging of 150k & 200k on their new model Diese truck
yes but now they make more torque i like diesel for an everyday car and gas for a weekend car
poseidonsr 2.0 SDI have 75hp and 140nm and fsi 140hp 200nm... u dont need turbo for torque lol
@@antoniotod9614 my 1.6dit subaru petrol engine has 250nm torque between 1800-4800 rpm.
Your math is wrong. You were supposed to compare torque/fuel, not torque/engine_configuration
Very awesome video, kudos
Awesome explanation !!