Figured some here would get a kick out of this article:
Nerd Alert! Mazda
The real meat, however, is on the final page:
Quote:
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Picture this: the spark plug sparks causing the detonation of the air:fuel mixture right around the plug. The flame front forms and spreads out and away from the central ignition point. The flame front burns the fuel and air in the cylinder as it moves through the mixture. This flame front increases the pressure and temperature of the unburned mixture in front of it. Sometimes, the pressure increases enough to cause combustion in the mixture before the flame reaches it creating knock.
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In other words, instead of creating enough pressure via compression to cause auto-ignition, the engine can create *almost* enough pressure via compression, and use traditional spark ignition of a very tiny amount of air-fuel mixture concentrated around the plug (basically, the way all direct injection engines do now to lean-burn) to push the mixture over the edge.
Very speculative, but I like the idea. Sort of the combustion equivalent of how we race in the rain... don't wait for the car to slide, push it over. Makes it more controllable.
Betcha this makes the calculations much simpler than in other HCCI systems.