5 Reasons Diesel Engines Make More Torque Than Gasoline

Why Do Diesel Engines Make So Much Torque?

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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[EngineeringExplained]

Hope everyone's having a great day, thanks for watching!

[Edvinas_Bartkus]

Hey Jason. Im a wiever from lithuania. My girlfriend calls you the torque guy because she hears you say that alot. Love your videos.

[kirk]

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.

[linamdiazv]

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!

[ytfazefan]

This channel taught me more that all of my years in school and college, thanks legend❤️

[ubertuber]

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...

[WilliamITA]

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/

[markhoult]

Hands down the best Youtube channel for so many reasons.

Jason could probs do the maths to prove it.

[rfmerrill]

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)

[mianarshed]

There were a couple of questions in my mind about Diesel engines, but after watching this video, everything is clear. Thank You.

[Bowhunter]

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.

[chucki]

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.

[johnnycaprice]

Steam engines- "Hold my beer."

[Dourkan]

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!

[toyotabrony]

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.👊🏼👊🏼

[Raptorman]

Jason, love your videos and I really appreciate your ability to convey complex topics in a way that mere mortals can understand.

[qasimmir]

Diesel engines are great, it’s a shame they’re being killed off.😢

[cantanto]

I admire people who are able to explain technical things so well! Thank you!

[alanhardy]

Excellent video that explains things very well, but perhaps It's also worth mentioning that although diesel fuel is more energy dense, it has a slower burn rate than gasoline, which imposes a limit on the maximum rpm at which a diesel engine can continue to produce power. That comes out at only around 4000rpm, and there's nothing to be gained by designing the engine to spin faster in order to do more work because the fuel won't be able to burn fast enough to keep up with the shorter compression/ignition cycles.

[yasir]

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