Quote:
Originally Posted by Shawn D.
Drag is a square function, power required is a cubic function.
The words used to describe that are "pinging" ("pinking" in the UK, Australia, New Zealand) or "detonation" (not the same as "combustion").
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Cubic/square, that sounds clear, thanks!
I'm familiar with both "Pinging" and "detonation" as names for the condition when fuel ignites by preassure/temperature from another location than the spark plug. If I have understood right, the noise comes from two wavefronts/pressure waves meeting with a sharp mechanical chock as a result.
What I tried to describe is a phenomenon that keeps the engine running for some second or even more the moment after the ignition have been switched off. -Same words in english?
Dirty spark plugs, plugs that run to hot or thick deposits of carbon in the cylinder head is probably the reason to this. Compression ratio and shape of the combustion chamber can also affect this. The worst case is when the engine start running backwards on the unburned fumes in the exhaust, since this will make the oil pump suck back some of the oil from the bearings.
Driving with a kill-switch means you are switching off the engine abruptly from medium revs at high load, wich is quite different to how most people drive. I do have old spark plugs, and perhaps they run a bit to hot for my type of driving. I have never noticed the slightest bit of this "hot bulb engine phenomenon" before I started Burn & Glide driving. With B&G I get it most of the times I kill the engine if I don't have at least perhaps 15% ethanol.
With 25-30% ethanol, the fuel/air-ratio is quite lean since the ethanol like ptjones wrote have less energy than petrol. This ratio seems to be close to the point where my carburettor and engine fails to ignite some strokes and beyond this point the fuel consumption will increase again and HC levels will raise abruptly. Perhaps an efficient CDI-system could push the limit a bit more than my old distributor/mechanical breaker can cope with.