Is there a small engine area on this forum? I.e. 2 strokes, weedeaters, chainsaws...etc?

[HusqvarnaRider]

Called pre-ignition. A hot bit of carbon, a sliver of metal that is hot enough to ignite fuel vapor. https://en.m.wikipedia.org/wiki/Pre-ignition

This is what separates mechanics from on-lookers.

Rev,.... Shouldn't it be called "Perpetual Combustion", since it continued to operate without a "Spark"?

And I'm actually familiar with it somewhat, as in the case of an Oil Burning Furnace, where the Oil Gun, pumped far above the normal amount of oil, in to the Combustion Chamber, but the Thermostat had shut down the "Gun". The "Refractory" in the Combustion Chamber was still hot enough to ignite the oil, which in turn, as the temperature rose, it activated the Blower. That action causes all kinds of Problems, ranging from Soot/Carbon Buildup in the heat-exchanger, to blowing the Oil Gun out of the Furnace, & Causing a Fire.

I'm not claiming to be a "Lawn Mower Mechanic", but I do understand "Combustion" due to my work in HVAC.

 

[Smithsonite]

Back in the day when carbureted cars did this, we called it "dieseling" ... because that's essentially what was happening - fuel was igniting by high compression caused by excessive carbon deposits, or igniting from glowing carbon deposits. Either way, it was no longer a spark-ignition engine at that point.

I had an '85 Monte Carlo that used to diesel so bad it would run on for almost 5 minutes! I'd have to stuff the pedal to the rug to get it to stop, HAHAHA! That thing hit everything but the lottery ...