donkeyking
Airman
- 35
- Dec 6, 2005
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Regarding detonation, why are there more chances to occur detonation in lean mixture than rich mixture when the engine uses the same fule?
For example Avgas 100/130, it is obvious this kind of fuel has more detonation chance in lean mixture than rich mixture.
Many thanks
Donkeyking
let's try this. liquid gasoline will not burn. if you are really brave a lit match can be plunged QUICKLY into a pool of gasoline and the match will extinguish. pure vapor will also not burn the same for hydrogen gas. combustion requires fuel PLUS oxygen. rich fuel mistures burn poorly, no oxygen. lean have more oxygen and burn quickly
i have actually done this, the container is capped and cooled to keep vapors condensed. remove the cap quickly and plunge the match quickly. it is only the vapors which are explosive
I have another question.
Does turbofan or turbojet engine has detonation problem?
thanks
Super lean ratios do not have the tendancy to detonate because of the cooling effect of the excess air.
Aircraft engines tend to have ineffcient combustion chambers so that doesn't help either.
I was having a bit of trouble with that tooI guess technically that could be true, only if your engine has so little fuel in the mixture that it will not ignite during the combustion cycle
Fuel quality and compression ratios are a huge factor in preventing detonation. A octane rating is a measure of a fuels resistance to burning. That is why high compression engines require high octane fuel. Higher compression makes more heat. Typical pump gas will only support on average 10:1, or 10.5:1 compression safely. Anything over that and you can can have trouble with engines knocking, pinging, or run-on after you turn off the ignition. Our open modified dirt track engines will be in the 13-14:1 compression ratio range with over 600hp, and racers will typically run 110 racing fuel, or straight methanol. It is actually better to have too much fuel than too little as too much fuel will flood your engine, but typically not cause any sever problems. A lean engine with detonation problems can destroy a new engine in a few minutes if the detonation is severe enough. We see racers all the time who have trouble with detonation either do to poor fuel quality, not enough fuel, timing problems, etc burning up $700 sets of pistons. There are many reasons detonation can occur, TEC's explanation in the #3 post is a good explanation.