"Gord Beaman" wrote in message
...
Bruce Simpson wrote:


To give you an idea of the difference (in terms of shock, vibration
and noise) -- in a deflagration, the flame travels at just a few
meters per second, in a detonation the flame front effectively travels
at several times the speed of sound.

Yes, the operative word here is 'effectively' because there's
actually no defined flame-front at all. As the normal flame front
progresses across the firing chambre a certain area of the
remaining fuel/air charge starts getting squeezed (and heated by
it) till it's internal temperature arrives at it's ignition point
then the whole remaining area detonates almost instaneously
producing an extremely high spike of pressure which is
practically useless against the inertia of the piston/crank etc.
This spike quickly punches and burns holes in the piston etc.

The big problem with regards to power from a detonation is
that it all most always occurs during the compression stroke.
During the normal operating cycle the spark is fired to ignite
the mixture substantially before the piston reaches the top of
the compression stroke, with the normal "slow" burn the flame
front hasn't burned far before the piston reaches top dead center
and started back down during the power stroke. Maximum
pressure is achieved during the power stroke.
The ignition for the detonation likely comes from a normal
spark event (there are other causes) but the environment in the
combustion chamber has put mixture to close to the ignition
point and it all -or portions of it- tip over the edge and start
burning before the normal flame front gets there.