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by skywal_l 1601 days ago
Diesel engines might not have throttle plate but they use injection which certainly do not inject air when acceleration is released, so the cylinders will act exactly the same way. Reading the web I see conflicting account on this subject. Strange...

Also, I though that modern petrol engines did not have throttle plates anymore and use the same injection system than diesel engines (no more carburetors).
2 comments
ska 1601 days ago
> use injection which certainly do not inject air when acceleration is released,

FWIW injectors don't inject air; the airflow is separate, get's compressed (and hence heated) then the fuel is injected, then bang (in diesel)

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garaetjjte 1601 days ago
>work the same way as 4cyl

I'm not sure what you mean, both Otto and Diesel cycles are four-stroke.

In petrol engines power is usually controlled by throttle plate which limits volume of air going into cylinder, and enough fuel is added during the intake stroke (either by injection or carburetor) to have combustion close to stoichiometric.

In diesel engines there's no throttle plate and engine always runs on lean mixture, and power is controlled only by amount of injected fuel, which is done after air is already compressed and hot.

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ska 1601 days ago
Point was injectors inject fuel not air...

I think we cross-edited, remaining confusion I think was about 2 vs 4 stroke but it's not really relevant so I had adjusted with a nod to when diesel injection occurs in 4.

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throwaway0a5e 1601 days ago
The fuel system doesn't provide restriction on the air going through the engine.

A diesel engine that's not dumping in fuel (because your foot isn't on the pedal) has about as much engine braking as a gas engine that's run out of fuel but the operator has floored the pedal.

A gas engine has a throttle that can restrict airflow. A diesel can either be equipped with an exhaust brake or compression brake. The latter is tons more effective but louder.

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