Cedric Chang nope9.com> writes: > I don't know the difference between burn fast and explode. Does fuel > burn fast and if the engine flies apart then the fuel was "exploding" ? In a 10,000 RPM 2-stroke engine total fuel burn occurs in less than 2 msec and it is not called an explosion. The spark timing must be more accurate than a tenth of that to avoid problems at high power. 200 usec does not sound like much for amicro but the rotation timing sensor must be at least twice as accurate over temperature, voltage and age. A normal car engine that revs up to about 5000 should finish burning anything in 4 msec or less, or there will be flame out the exhaust. An explosion occurs when the mixture goes off faster than the speed of sound in it (see deflagration and detonation on Wikipedia). At the speed of sound at STP in a 1 inch bore engine the flame needs 350 usec to reach the cylinder wall from the central spark plug. So if the engine must burn in under 2 msec but 350 usec is the limit for detonation (actually it is more complicated than that but this is just a beer coaster explanation) the 'normal' operation is *extremely* close to detonation regime (known as knocking), and remember that the transition is exponential (flame speed grows exponentially as conditions near detonation conditions). Peter P. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist