"Friedrich Ostertag" wrote:

Hi Gord (and Peter),

Why must knock be supersonic?

Peter Skelton

Well, it's not exactly supersonic actually, it's more like
'instantaneous'.

It's actually two different things. "Detonation" means supersonic
combustion. "Knock" means preignition of part of the charge before it
is reached by the flamefront (or in extreme cases the whole charge even
before the spark). However one can lead to the other and the result is
pretty much the same anyway: extreme pressure gradients. Therefore the
terms are sometimes used interchangeably.

Less than a half minute with heavy detonation
wrecked it. Don't futz around with detonation!. It'll bite yer
butt!.

true ...

regards,
Friedrich

Yep...very good Friedrich...that's exactly as I see it...one
point, you use the term 'preignition' and although I see how you
meant it now (and you're correct) I never use that term unless
I'm describing the occurance of spark, it can be confused with
that..

A little levity for a sober subject. Our 'dash one' for the Argus
describes detonation like this.

"Detonation will be evidenced by a rapid rise in cylinder head
temp, a rapid rise in oil temp, a rapid drop in torque closely
followed by structural parts of the engine emitting from the
exhaust stacks"

I think they used that to scare the snot outta us engineers (it
worked too!)
--

-Gord.