Hi Peter

diesel engine will intake pure air, compress it (much further than
a
gasoline engine compresses the mixture - temperatures get really
hot
just from the adiabatic compression), and then injects the fuel
into
the compressed (and hot!) air, where it immediately ignites due to
the
high temperature of the compressed air. Thus my comment, that the
fuel
cannot preignite, as it is not there prior to the time it is
supposed
to ignite. No preignition - no detonation.


actually you were fine down to this point. what you mean is that when
ther is no "premixing" there is no detonation. Detonation involves a
supersonic combustion wave moving through the mixture.

good point. The proper definition of detonation in general is
supersonic combustion, as you pointed out. The proper term for what
happens, when the fuel-air mixture or part of it on a spark ignition
engine preignites, would be "knock". However quite often the two terms
can be heard used interchangeably when discussing engines, because the
result is very similar as far as the engine is concerned. Both lead to
a much higher pressure-gradient in the cylinder. And it is really
difficult to tell, whether a portion of the mixture preignited before
it was reached by the flamefront, or whether the combustion went
supersonic and just got there quicker.

In any case, both will never happen on a diesel engine.

good discussion at
http://www.safetynet.de/Seiten/articles/CMRNov99.pdf

very interesting paper, thanks.

regards,
Friedrich

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