Engine braking
Discussion
I have driven petrol cars and diesel cars and can't say that I noticed much difference in the engine braking between either, but I read somewhere recently that diesel engines cannot 'engine brake' at all due to their design.
I am not sure how I have managed to drive for 20 odd years without knowing that!
Has anyone got a technical explanation for why diesels can't engine brake?
I am not sure how I have managed to drive for 20 odd years without knowing that!
Has anyone got a technical explanation for why diesels can't engine brake?
Ayahuasca said:
I have driven petrol cars and diesel cars and can't say that I noticed much difference in the engine braking between either, but I read somewhere recently that diesel engines cannot 'engine brake' at all due to their design.
I am not sure how I have managed to drive for 20 odd years without knowing that!
Has anyone got a technical explanation for why diesels can't engine brake?
You read incorrect information.I am not sure how I have managed to drive for 20 odd years without knowing that!
Has anyone got a technical explanation for why diesels can't engine brake?
Well I never.
wikipedia said:
Petrol (gasoline) engines
The term engine braking usually refers to the braking effect caused by throttle position induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
When the throttle is lifted less air is allowed to pass through the intake manifold, and the engine works against this vacuum. It is the deceleration of the engine against this vacuum which provides the braking effect.
Diesel engines
Diesel engines vary fuel flow to control power rather than throttling air intake and maintaining a constant fuel ratio as petrol engines do. As they do not maintain a throttle vacuum, they are not subject to the same engine braking effects as petrol engines are.
The effect seems pretty pronounced on diseasels I've driven. The term engine braking usually refers to the braking effect caused by throttle position induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
When the throttle is lifted less air is allowed to pass through the intake manifold, and the engine works against this vacuum. It is the deceleration of the engine against this vacuum which provides the braking effect.
Diesel engines
Diesel engines vary fuel flow to control power rather than throttling air intake and maintaining a constant fuel ratio as petrol engines do. As they do not maintain a throttle vacuum, they are not subject to the same engine braking effects as petrol engines are.
miniman said:
Well I never.
You do know who rights Wiki dont you ?wikipedia said:
Petrol (gasoline) engines
The term engine braking usually refers to the braking effect caused by throttle position induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
When the throttle is lifted less air is allowed to pass through the intake manifold, and the engine works against this vacuum. It is the deceleration of the engine against this vacuum which provides the braking effect.
Diesel engines
Diesel engines vary fuel flow to control power rather than throttling air intake and maintaining a constant fuel ratio as petrol engines do. As they do not maintain a throttle vacuum, they are not subject to the same engine braking effects as petrol engines are.
The effect seems pretty pronounced on diseasels I've driven. The term engine braking usually refers to the braking effect caused by throttle position induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
When the throttle is lifted less air is allowed to pass through the intake manifold, and the engine works against this vacuum. It is the deceleration of the engine against this vacuum which provides the braking effect.
Diesel engines
Diesel engines vary fuel flow to control power rather than throttling air intake and maintaining a constant fuel ratio as petrol engines do. As they do not maintain a throttle vacuum, they are not subject to the same engine braking effects as petrol engines are.
pinchmeimdreamin said:
miniman said:
Well I never.
You do know who rights Wiki dont you ?wikipedia said:
Petrol (gasoline) engines
The term engine braking usually refers to the braking effect caused by throttle position induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
When the throttle is lifted less air is allowed to pass through the intake manifold, and the engine works against this vacuum. It is the deceleration of the engine against this vacuum which provides the braking effect.
Diesel engines
Diesel engines vary fuel flow to control power rather than throttling air intake and maintaining a constant fuel ratio as petrol engines do. As they do not maintain a throttle vacuum, they are not subject to the same engine braking effects as petrol engines are.
The effect seems pretty pronounced on diseasels I've driven. The term engine braking usually refers to the braking effect caused by throttle position induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
When the throttle is lifted less air is allowed to pass through the intake manifold, and the engine works against this vacuum. It is the deceleration of the engine against this vacuum which provides the braking effect.
Diesel engines
Diesel engines vary fuel flow to control power rather than throttling air intake and maintaining a constant fuel ratio as petrol engines do. As they do not maintain a throttle vacuum, they are not subject to the same engine braking effects as petrol engines are.
Without a throttle, a diesel engine does not have to pull the piston down against the intake manifold vacuum, so theoretically a diesel has less engine braking than a gasoline engine by 0.7bar BMEP. BUT, modern diesels have throttles, and the deccel you actually get when you let go of the throttle these days is a carefully controlled negative torque demand, so you never really see the "raw" effect of trailing throttle like you used to.
A little off track but sort of relevent-ish. I was followed along one of my favorite roads when I had my BMW E36 track day car. Turned out it was a Police car. I had pulled into a petrol station when the officer asked me....
"You like to lift off a few seconds before you brake for corners; don't you?"
"Yes, why do you ask?"
"The two foot flame out of your exhaust a few seconds before your brake lights come on gives you away".
Very nice chap, we had a chat about cars and stuff until he got called away ten minutes later.
"You like to lift off a few seconds before you brake for corners; don't you?"
"Yes, why do you ask?"
"The two foot flame out of your exhaust a few seconds before your brake lights come on gives you away".
Very nice chap, we had a chat about cars and stuff until he got called away ten minutes later.
Engine braking is caused by pumping losses, so a diesel will had the greatest effect as they always fill the cylinders and have much higher compression.
Engine braking is not caused by a throttle vacuum.
So diesels do engine brake, more so than petrols.
Automotive development engineer:1
Wikipedia:0
Engine braking is not caused by a throttle vacuum.
So diesels do engine brake, more so than petrols.
Automotive development engineer:1
Wikipedia:0
Cost Captain said:
Engine braking is caused by pumping losses, so a diesel will had the greatest effect as they always fill the cylinders and have much higher compression.
Engine braking is not caused by a throttle vacuum.
So diesels do engine brake, more so than petrols.
Automotive development engineer:1
Wikipedia:0
You know the best thing about Wikipedia? If it's wrong, you can put it right!Engine braking is not caused by a throttle vacuum.
So diesels do engine brake, more so than petrols.
Automotive development engineer:1
Wikipedia:0
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