[Corvettaholic]

Its generally known that gasoline in an engine is supposed to explode at the correct time, but sometimes it blows up before its supposed to. This can happen for a number of reasons, but the one I'm concerned with is heat. If the cylinder is too freaking hot, or the spark plug is too hot, then the gasoline will detonate well before its supposed to. How do you figure out how much heat causes this? I have a project that uses the same idea of not wanting the gasoline to explode until just right, but I need to know how much heat I can have sticking around before, say, 100ml of aerated gasoline goes boom. Any ideas on this? If you guys (as in the regulars) want to know the details of the project, I'll let you know through PM because I'm unsure of the appropriateness for this site... but I think the heat tolerance before ignition is a valid question  

[ATMyller]

That's simple. If cylinder's temperature exceeds fuel's flash point it will pre-ignite. And compressing the cylinder increases the inside temperature. So you can calculate the ingnition heat with gas laws if you know initial heat and cylinder measurements.
But remember that gas laws don't include heat conducting through the cylinder wall.

[Corvettaholic]

Well I used the car example to illustrate the potential problem I'll have with heat. In my project, there will be no compression whatsoever, the thing I'm worried about is conduction, and residual heat from rocket motor exhaust. Take your standard hobby shop B rocket motor for instance. When that engine burns off, how hot is that exhaust? If anyone knows, great, otherwise I'm going to clamp one to my work bench and stick a high temp thermometer behind it. Anyone know of a cheap thermometer that can handle model rocket exhaust? The main thing I'm worried about is staying well away from the flash point of gasoline that has evaporated. I want to avoid evaporation if at all possible, but I don't think thats going to happen. The only place gasoline in a gaseous state should go is in my engine! But I have to plan for other possibilities.