Pre/post ignition

[Clare Snyder]

Bruce Plecan wrote:
> 
> As I recall from a Texaco Research Film (?) from the early 70's,
> in a series of variable compression engines they were able to
> generate a pre-ignition event at 5-7d pre ignition.
>   If someone has something more current/up to date, I'd like to
> hear it, cause the neural net involved with this is an old set.....
>   Just to stir things up,  wouldn't the most viotile stuff react first,
> leaving little or nothing combustable, for a post event?.
>   Cheers
> Bruce
>From what I remember from my trade school days (both as a student, and
later as an instructor) the primary differentiation is between
pre-ignition and detonation. Now, in a practical sense, preignition
CAUSES detonation sometimes - the fuel gets squeezed a bit too hard, the
cyl is a bit too warm, the octane is a bit too low, and the fuel
detonates, or appears to. Sometimes it just burns normally, but because
the ignition starts too soon maximum pressure occurs too early, and the
engine knocks. Other times it starts out that way, but due to extreme
conditions, the fuel starts to burn from the other side of the cyl as
well, and you have detonation. The differentiation between pre-ignition
and detonation is pre-ignition happens before the spark. Over advanced
ignition does not cause pre-ignition. It does cause spark knock.This
spark knock is the result of the formerly mentioned pre-ignition
detonation.
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.
So, pre-ignition is a pre-spark event, while detonation is usually, and
for the purposes of general discussion, a post spark event. Hope this
helps CLARE-ify things for some.
-- 
                               _/\_
                       --|-----([])-----|--
                         S    0/  \0    B
         Alls well that ends well!! www.snyder.on.ca is back
                  E-Mail service is back to normal
                  To avoid bouncing E-Mail messages
                    Reply to Clare at snyder.on.ca
                                OR
Remove the R from clsnyder in my E-Mail Address to reply. Stop the
spammers!!!
It's hard to soar like an eagle when your stuck with a bunch of
Turkeys!!!