Maximum advance

[David Hunt]

----- Original Message -----
From: "Greg Hermann" <bearbvd at cmn.net>
>
> Also sonic effects--as in pressure changes can only equalize themselves
> across the entire chamber at Mach 1. (Which of course varies with the
> (changing) molecular weight of the gasses and with the (also changing)
> (square root of) the absolute temp of the gasses. Nope, gas density and
> pressure have no effect on Mach 1!

I'd like to point out that you can't increase pressure without increasing
temperature.  So if you change one you change the other. You know A = B and
B = C so A = C.  The speed of sound at ground level is different than the
SOS at altitude.

Also, the 'burning' gas can certainly exceed Mach 1,  that's the crackle in
a top fuelers report.  The nitro can do it because of self contained oxidant
doesn't require mechanical mixing.

The time to traverse the 1" vertical dimension in the exhaust chamber is 75
microseconds at 1100 fps.  The time to traverse from spark plug location to
the furthest wall is 227 uS if the that wall is 3" away.  For an engine
turning at 6000 RPM this is (0.075/10) * 360 and (0.227/10) * 360 or   3
degrees and  8 degrees respectively.  Therefore, I assume that the speed of
the flame front is not limited by the speed of sound in normal combustion.
Since there is no correlation between pressure and torque when the crank is
TDC, I suspect that if an engine is timed to 32degrees BTDC that maximum
pressure occurs much after TDC.

Does anybody know what the emissivity etc is of an air gas mixture?  I
suspect that when knock occurs the radiant effects become relatively more
significant.  Is anyone certain?

dh





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