Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Mon, 30 Sep 2002 09:56:03 -0400
Message-ID: <redirect-1794217@logan.com>
From: "Gary Casey" <glcasey@adelphia.net>
Subject: Detonation
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<<Fuel doesn't cool the engine.

Fuel alters the burn rate and that alters the location (in relation to TDC)
of the 50% burn time for the charge - - and that alters the peak combustion
pressure and temperature - - and therefore, the rate of heat transfer into
the cylinder.

One can get into all sorts of misunderstandings if one treats fuel as a
coolant, rather than something that modifies the rate of burn of the charge.

Regards,  George >>

Exactly right, George.  Excess fuel makes a good detonation suppressant.  I
was too loose with my analogies.  Modern car engines have been pushed to
higher compression ratios partly by using richer mixtures as well as
retarded spark timing to reduce detonation in response to knock sensor
inputs.  At light loads during the emissions test retarded timing is used
and then at full load when pre-ignition could otherwise be a concern richer
mixtures are used.

I suppose you could use water injection as a detonation suppressant, but it
is just easier to use fuel.  And then you avoid all those comments about
carrying water on an airplane....

Gary Casey