Motorsports Village

Lean Detonation?
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Author:  jmarkaudio [ Mon Mar 21, 2011 2:57 pm ]
Post subject:  Lean Detonation?

I put this here as it has to do with my E85 endeavor, what I wonder is what really happens to cause an engine to detonate or burn up from being lean? As I have had mine to the point of being stupid lean, surging from the bad regulator as well as being .020 in jet size down from my current tune and still not hurt anything or shown any signs of damage I wonder if this is E85 related or is it due to the way the engine is tuned. More directly, what causes an engine to be hurt from being too lean? I would think too lean would not make as much power or produce as much heat, as long as the ignition is capable of firing the mixture, and not hurt it. I know some use the excess fuel as a cooling tool, but if the timing, plug heat range, and engine heat are correct do you need that? Assuming correct fuel as well.

Author:  rick360 [ Mon Mar 21, 2011 8:27 pm ]
Post subject:  Re: Lean Detonation?

I don't think you will ever hurt a typical drag engine from racing it lean. It's not at full power long enough to hurt it from lean. If your fuel is not enough octane, that is another story and can detonate enough to hurt parts. I've always jetted up or down and NEVER worried about whether it was lean or not, just whether it picked up ET/MPH/Power on the track or on the dyno.

Circle track where its at WOT for longer periods of time is another story, but I don't think is as easy to burn one up as most think. If you go more than a little lean the EGT will go down. (with gas anyway).


Author:  shrinker [ Thu Apr 07, 2011 1:11 pm ]
Post subject:  Re: Lean Detonation?

Piston damage from lean condition occurs due to removal of the boundary layer of gas on the surface of the piston. The boundary layer is removed or disrupted due to pressure waves of combustion originating within the layer. (Fancy words for detonation). The reason why the detonation occurs within the layer is because the Oxygen molecules have become too hot, theres not enough fuel to create a under-supply condition of oxygen. (Fancy words for its too lean). The hydrogen phase of the burn is fast and violent and releases 60% to 70% of the energy of the total burn so when its lean the oxygen thats not used yet absorbs a considerable energy increase and gets too excited and starts going off by itself doing its own thing, (non fancy words for detonation). CO production requires nearly as much energy input as the release so lean conditions dont get the temperature stabilisation time of a CO reaction. Basically its get hot real quick.

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