Diesel Vs. Gas-Torque Question

[Graeme H Burvill]

I was asked today why a diesel engine puts down so much more torque than a gas engine. I didn't really know the answer, but I figured it was down to how diesel burns compared to gas. Honestly I have no idea though, i really don't know anything about diesel engines. Anyone able to shed some light on this for me?

[Brett Haviland]

longer stroke and bigger displacement.  Plus it uses diesel instead of gasoline, which means that diesel fuel has more energy availible inside of it then highly volitile gasoline.

[Shane Sawatzki]

wayyyyyyyyyyy higher compression, no need for spark plugs, the compression is so high the diesel just ignites. along with what brett said about the bigger displacement and longer stroke

[Remi Raymond]

Brett sort-of nailed it.
Diesel has higher potential energy in it for when it goes boom
The mechanical side (bore, stroke, rpm, compression etc..) is just how the energy is extracted.

It's actually the same science behind low vs high octane power production potential for the same reasons, Diesel is just much higher up the same scale.

higher octane is made by cooking crude oil for less time
if you take it out a bit early, you have high octane
if you take it out when it's still raw inside, you have diesel.

Or something like that, anyway.

[John Hartman]

yep, more chemical engergy per unit of fuel.

So, for the same amount of burned fuel you get more energy.

Its also why they get better mileage for the same sized engine.

[Richard Steger]

"The air is compressed much more than is the case with a gasoline engine, then near the point where the piston reaches the end of its compression stroke, fuel begins to be injected at high pressure. Within about a millisecond after fuel injection begins, the fuel ignites in the hot, highly compressed air. Combustion continues as fuel continues to be injected until some time after the piston begins moving down again, then the hot gases push the piston down the power stroke." quoted from: http://www.tdiclub.com/TDIFAQ/TDiFAQ-6.html   So the combustion event is much longer in duration during the power stroke and is controlled by the fuel injection process.  With newer common rail setups, piezo injectors have multiple injections per power stroke.  Even modern Direct Injection gassers have a short combustion cycle because although the direct injection of the fuel charge reduces possible detonation and permits increased compression ratios, combustion is still initiated by a spark, therefore of short duration.   http://www.bankspower.com/techarticles/show/27-Why-Diesels-Make-So-Much-Torque  This page states that the combination of the greater thermal energy of the fuel, leverage of long stroke engines and length of combustion causing higher cylinder pressures gives diesels their greater torque.