Re: Math question about engine cylinder volume/pressure
Ok....I got it.......Was just doing some reading about cranking pressure and how it's calculated. Since valve timing affects the volume of the cylinder the numbers in this example will ultimately not be usable in predicting the cranking pressure...but I can show you the math. To predict the number accurately we would need to know the effective stroke and effective compression ratio based on the valve timing, since the valve doesn't open at top dead or bottom dead center. Anyway....here is how they calculated the cranking pressure.
Cranking Pressure (absolute) CP = (CRE^1.2 ? AP) where CRE = Compression Ratio, Effective and AP = Atmospheric pressure
"At cranking speed, the absolute cranking pressure (?CP?) is a function of the 1.2 power of the effective compression ratio (i.e., for 8:1 compression ratio, use 8^1.2) times atmospheric pressure (14.7 psi @ sea level, &c.). This adjustment (1.2 power) is a polytropic value used in preference to the traditional adiabatic value (1.4) for the ratio of variable heats for air and similar gases at the temperatures present. This compensates for the temperature rise caused by compression, as well as heat lost to the cylinder. 1.2 is not accurate in all cases, since the amount of heat lost will vary among engines based on design, size and materials used, but provides useful results for purposes of comparison."
So for our example we have the published compression ratio of 8.8...the effective ratio would be less than this. 8.8 ^1.2 = 13.6.....13.6 x 14.7psia = 199.8 absolute pressure or 185 psig....Final Answer Regis
, Isuzu was using the ionization readings through spark plugs all the way back to the year 2000 on the multi-port injected 3.2L V6.