Agree completely. "Lean mixture melts pistons" is a myth.Tommy Cookers wrote:maybe it's unfair to asume the pistons will unavoidably be hotter as the air is relatively more than in any previous SI engine, and the heat rate (fuel burnt per piston) seems hardly more than with the NA V8s
Absolutely! One thing detonation does is destroy the boundary layer (locally). That's how it melts the piston.PlatinumZealot wrote:Yes makes sense. Though jet engine blades are kept cool by air or steam. That reminds me of another thing. Boundary layer control. Maybe keeping the bounday layer of the air above the piston intact is a priority.
Pre-ignition without accompanying detonation produces adverse pressure peaks but not the thermal failures you describe. However pre-ignition normally causes detonation and the detonation is what causes the failure. End-gas detonation usually occurs near the edge of the chamber and accelerates convective heat transfer into the nearest point on the piston crown, by scouring through the boundary layer with intense local turbulence and shock waves. The intense local heating softens the aluminium and soon results in increased blow-by at that location which of course is a positive feedback mechanism producing ever-increasing local heating and catastrophic failure.Brian Coat wrote:GG:"One thing detonation does is destroy the boundary layer (locally). That's how it melts the piston"
Have you encountered much thermal failure directly induced by detonation as a primary root cause?
I've detted one or two pistons to destruction in my time and I've not yet managed this. I find that normally (ha!) the detonation will mechanically destroy top land,/fire ring/other, with comedy thermal consequences served as the second course.
In my experience, direct thermal failures are more commonly pre-ignition-induced.