Therefor requiring the higher octane/high test stuff because it has a higher flash point...
IIRC, this is not accurate. Detonation of the endgas has little to do with flash point per se, and more to do with the increasing pressure and temperature (over time) "cooking" the endgas and breaking down the more unstable molecules into molecules more susceptible to spontaneous ignition. Pure octane is less prone to being "cracked" than pentane, heptane or septane. You can have 2 engines with equivalent CRs, and one may have a lower octane requirement than the other because it limits the time that the endgas is exposed to dissociating heat and pressure. Such things as spark plug location (effects max distance the flame front has to travel), swirl and turbulence, quench (squish area), and engine speed all have an effect on the endgas.
I think temperature might be too simplistic, because that implies if you could raise the intake charge's temperature by 10% Kelvin (about 40C or 100F *edit - Oops, should be 30C or 70F. Did the math while tired. - end edit *) that you would also increase its power (or decrease its rate of fuel use) by about 10% (assuming detonation didn't wipe out the benefits). That could mean that a non-intercooled turbocharged engine might be the best way to go for part-throttle fuel efficiency. I think that at the very least that automakers would not have deleted hot-air risers on newer engines.
*edit - Forgot to mention that the dissociation in the endgas is greatest at peak temperature and pressure, not at those (normally) created prior to ignition. FWIIW... - end edit *
Please do not take my comments as criticism or saying that you are wrong. My arguments/comments are rather indirect and somewhat "anthropic" (something has to be a particular way otherwise we wouldn't be where we are), that if something simple existed then the automakers would be exploiting it. (PLEASE, no conspiracy theories. Ferrari/Porsche/racing teams wouldn't hobble themselves to appease OPEC/Military-Industrial-Complex/The Illuminati.) At the same time, my goal means I am mis-anthropic, because I believe that there is something that the automotive geniuses are not exploiting. (My mind is a confused place at times!
A supposition: What would happen if you increased the amount of non-reactants into the intake charge when at part-throttle? This would increase the effective CR, and the charge temperature, at the time of ignition. (This does introduce other combustion-time issues, which might be interesting to explore...) Would this increase the TE?
Edited by NorthWet, 02 May 2009 - 01:38 AM.