Knock S., VE, CR

[Jim Fitzgerald]

	I found some more Knock S. Info in "Automotive Elect Handbook" by
Ronald K. Jurgen (McGraw Hill).  Author says that knock frequency ranges
from 2 to 15 kHz and is given by:  "Drapers Equation"   Fr = Pmn(C)/pi(B)
Pmn =  vibration mode constant
C   =  velocity of sound in Cyl. gas
B   =  radius of cylinder
	He gives an example, that with gas temp of 2000K,  velocity C = 900
m/s, and for a 100 mm Dia cylinder the 1st knock harmonic would be 5.75 kHz.
	So looking at the equation you can see that freq. is proportional to
cylinder dia. Using the same constants and  Fr = .0575 B you can
estimate other size cylinders.  He also says that any cyl knock travels
through the engine block to the sensor in less than 1 ms.  And that the
successive cylinders are consecutive in time and are not overlapped.  At
6000 RPM they would be 2.5 ms apart.  He says Manuf. originally tried to
tune the sensor to a particular freq. and that they had a Q factor of
about 2.  He thinks that they now use a filter in the ECM.  This was all
referenced to SAE papers 920702, 920808, and 910858
	Actually I think that most common KS are similar and if someone wanted
to tune the KS response for a particular app, that a simple RLC band
pass filter would be sufficient.
	On another note, I think that an engines compression ratio, both static
and effective, and the VE are strictly determined by the mechanical
design of the engine.  It would be the same if the engine were driven as
an air compressor.  Its the cylinder pressure curve that changes
depending on the characteristics of the intake charge gas mixture, 
Temp, Ing. Timming and all the other combustion variables.  
	Its also commonly known that lean mixtures can lead to burt pistons and
valves. Is that because the excess O2 is burning the metal (cutting
torch) while the overall combustion temp. is cooler??
Jim F.
----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org