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Author: Subject: Diesel Engine Questions
phelpsa

posted on 5/12/10 at 08:57 PM Reply With Quote
Diesel Engine Questions

Why does brake efficiency increase with load when there is no throttle to introduce pumping losses proportional to load?

Why does the amount of power lost to coolant decrease as load is increased?

Any input or help would be very much appreciated!

Adam






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steve m

posted on 5/12/10 at 08:59 PM Reply With Quote
Also why are diesels so bloody noisy when cold ??
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dinosaurjuice

posted on 5/12/10 at 09:24 PM Reply With Quote
not sure exactly, but there farrr superior to petrol engines IMO of course
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martthefridgeman

posted on 5/12/10 at 09:33 PM Reply With Quote
Normaly aspirated or turbocharged ?
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LBMEFM

posted on 5/12/10 at 09:49 PM Reply With Quote
Diesel "knock" is louder when cold because it's the sound of the cold diesel oil travelling through the injector, as it warms up it becomes thinner and therefore quieter.
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phelpsa

posted on 5/12/10 at 09:56 PM Reply With Quote
quote:
Originally posted by martthefridgeman
Normaly aspirated or turbocharged ?


I know that the test engine was turbocharged, however we weren't officially told this which would lead me to believe it shouldn't matter....






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steve m

posted on 5/12/10 at 11:08 PM Reply With Quote
" Diesel "knock" is louder when cold because it's the sound of the cold diesel oil travelling through the injector, as it warms up it becomes thinner and therefore quieter"

plausible, but sureley incorrect, as the diesel no mater what temperature the engine is, will still arrive at the injector cold

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RazMan

posted on 6/12/10 at 12:10 AM Reply With Quote
I thought it had something to do with the glow plugs pre-igniting the mixture. Definitely something about the timing of the burn IIRC - maybe the burn is retarded when it is cold?

[Edited on 6-12-10 by RazMan]





Cheers,
Raz

When thinking outside the box doesn't work any more, it's time to build a new box

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SeanStone

posted on 6/12/10 at 12:50 AM Reply With Quote
The diesel works by pressurising air without the presence of fuel, only injecting it just before peak pressure and temperature is reached. The peak temperatures will be lower when the engine is cold so I can only presume that will cause later combustion of fuel, resulting in a more prominent knock, possibly from the resulting natural retardation of combustion!
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