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Originally Posted by veilsidebr
Diesel engines have more compression ratios than ottos engine. This is one of the factors. What increases torque, in any engine, is the bore. How more bore you have on an engine, how torque you will have, because the area of explosion would be higher. Less bore and much stroke increase the revs of a car.
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Wrong way round i think mate, larger stroke more torque and revs less freely. As the con rod has a larger moment about which to turn the crank with a larger stroke. But there is a higher rotating inertia in the bottom end then , so it doesnt rev as freely.
Power = torque x angular velocity, so due to diesels not reving high, due to the high compression ratio and no real need to, the bhp figures are low.
As was stated before, the combustion in a diesel cycle is assumed to take place under constant pressure, and is ignited by detonation. So the force downwards takes place over a longer period of time. Where as the otto (petrol) cycle is not considered to be constant pressure combustion, but constant volume, so the combustion is more or less immediate.
If u ask again in a years time i mite b able to b of more help, after ive started the specialist course on combustion!!
cheers