Pre/post ignition

[garfield at pilgrimhouse.com]

On Thu, 21 May 1998 22:31:24 -0400, Clare Snyder <snyder at huron.net>
wrote:

>When an engine is running too hot or too lean, or has too high a
>compression or too low an octane fuel, the flame front propogation from
>the plug causes enough heat and pressure to cause the fuel to
>self-ignite elsewhere in the cyl, and the two flame fronts collide. This
>is referred to as detonation.

OK, this makes more sense. I was having a tough time imagining post-ign
events that were BEYOND the normal flame propagation time. Couldn't see
how this would be possible. What you're decribing above would say that
the ionization current would rise faster and higher, due to uneven and
more sudden/violent combustion explosion, and this lines up perfectly
with both the time issues AND the fact that detonation raises temps and
pressures way above normal. So detection of pre-ignition would be a
simple matter of finding ionization BEFORE the spark window, but
detection of knock/detonation involves distinguishing normal from
abnormal ionization current-level/waveform-maybe WITHIN the
post-ignition window, so it's not merely a matter of timing in the case
of knock. NOW that's making more sense to me. Thanks. The fractions are
beginning to add up. B)

Gar