[6pack] [TR] Compression boost

[Sally or Dick Taylor]

Kendall---Chapters in books have been written about this phenomena, but let's see if this can be shortened.

PREIGNITION occurs when the charge (air/fuel mix) fires without benefit of the engine's normal spark event, such as hot spots somewhere in the combustion chamber.

DETONATION is what gasoline does. We want it to, as this is what drives the engine. What we don't want is for a second detonation to take place while the piston is rising.
This other detonation occurs when excess pressure has built up at the flame front, at the top of the piston, and creates a "second" flame front. This second front is usually started at the opposite side (of the piston) from the spark plug. When the two fronts meet before the piston reaches TDC, a knock occurs. Delaying the spark timing, either thru a physical setting by the tuner, and/or thru some automatic device that senses pressure or knock, can reduce or eliminate this destructive force.

Fuel that has a higher octane is slower burning, which gives pistons more time to "reach the top" before another detonation can occur.

Cooling down the (air/fuel) charge is another way to reduce or delay detonation. This can be done by lowering the CR, or the temp. of the fuel or air.

Any help?

Dick


-----Original Message-----
From: Kendall Larsen
Sent: Tuesday, June 17, 2008 9:54 AM
To: 6pack List
Subject: Re: [6pack] [TR] Compression boost

This topic reminds me of something that Ibve never quite understood about
pre-detonation pinging and knocking.
B 
We talk about smoothing out combustion
chamber hot spots, higher octane gas, and spark advance after boosting the
compression ratio. But I donbt understand how spark advance plays into it.
Isnbt the pre-detonation a result of the air/fuel charge igniting before the
spark anyway? 
B 
Anyone want to layout what the factors are in all their
technical glory?
Kendall
San Clemente, CA
(engine under going AUTOpsy right
now, details to the list soon)
6pack at autox.team.net
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