PPRuNe Forums - View Single Post - Detonation caused by lean mixture
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Old 3rd Nov 2011, 05:08
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Big Pistons Forever
 
Join Date: Jan 2004
Location: Canada
Age: 63
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It is very difficult to get a non turbocharged carburated engine to detonate. Assuming proper fuel about the only way I would think detonation could possibly occur would be a prolonged low airspeed climb with the carb heat full on and the engine leaned to 50 rich of peak. This will result in very high CHT's due to the heated induction air and hottest flame from a "best power" mixture. Under any normal operating procedures the risk of detonation is virtually zero. This is doubly so for the run of the mill 4 bangers because they were all designed for 80/87 0r 90/96 fuel but usually operated on the far more common 100 Octane 100LL fuel, which will dramatically increase the detonation margins.

It is a different story however for some of the high output turbocharged engines. These engines can, even in "normal" operation have very small detonation margins. There was a spate of early inflight engine failures caused by detonation in early Piper Malibu's for instance. These engines must be operated with care to keep the CHT's down and respect the EGT and TIT limits.
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