Rob:

We are amassing a rather substantial volume of engine monitor downloaded data of real events. When comparing these to KNOWN test stand data, we can determine the actual change of events in the flight data. We have one engine which was run under a considerable amount of detonation with NO detrimental results. We have now seen several events which were clearly pre-ignition; one which started out as detonation with a progression into pre-ignition. You can see in the data, when the plug failed and the vent became self-limiting.

George did an exhaustive study of all of the NTSB cases where either detonation or pre-ignition were listed as causal agents (the stack of paper was four feet tall). The review of that data suggests that most of the catastrophic events are, in fact, not detonation, but pre-ignition.

We have now had enough real-time and recorded experience with detonation to be fairly comfortable with our understanding of what it is and is not. It is as you described. It is not as detrimental as we have always assumed. Engines can sustain hours of detonation without harm and there are actually some TC'd engines which experience light detonation routinely on takeoff. Pre-ignition, OTOH, is UGLY. It's the bad actor of the pair. It can destroy your engine in 30 seconds.

What we have come to believe is that detonation is basically not an issue at all in NA, conforming engines being run on conforming fuel.

Walter


On Mar 26, 2005, at 9:26 AM, REHBINC@aol.com wrote:

In a message dated 3/25/2005 10:49:10 PM Eastern Standard Time, Walter@advancedpilot.com writes:
Thank you for the thorough explanation of the event s as you understand
them.

**Both problems are commonly lumped together and low octane and high
cylinder temps can result in either one. When preignition gets bad, it
will destroy the engine faster than detonation. It also is harder to
detect preignition before serious damage is done.**

Both are commonly but incorrectly lumped together.  They are two very
different events. 
Walter
 
I guess my atrocious english is rearing its ugly head again. You are quite correct and that is how I should have worded my statement.


Further, the data indicates that it is actually quite likely that
damage from detonation as you have listed and is commonly sited is
really a result of preignition.  We have observed extended periods of
detonation in which there is no damage whatsoever to the cylinder,
rings, valves, etc.  I realize that this is counter to the conventional
wisdom, but it is in harmony with the observed data.
Do you have a source for the data you refer to? I would like to read up on it.
 
I was fortunate enough not to generate very much data of my own. Just two broken pistons and one broken ring. I scattered two engines, but that was due to alternate forms of stupidity.
 
Rob