Quote:
Originally Posted by RustyLugNut
HCCI engines which ignite all the fuel within a short time frame are markedly different from early attempts. You are correct in assuming the dwell time at or around TDC ( top dead center ) is important and juggling crank stroke and connecting rod length will be needed to maximize advantages gained from contracted ignition/combustion events. However, a smaller gain can be derived from simple elimination of ignition lead time. I think you will agree in the classic discussion of ignition lead time that less lead is more efficient. An engine, under a specific load/rpm will be more thermally efficient if it's ignition lead is smaller to produce the specified power. We had another thread, which I should revive again, where pfgpro put up some very good graphics of pressure curves for combustion. It made it clear that the pressure rise before TDC is all negative work and lost energy. If you can contract combustion and reduce lead timing, you can gain back that energy. This can be done on any engine with varying levels of success. Pfgpro has shown this with some measured runs on his modified engine and his leaky nitrous "experiment" showed us a hint of what could be gained by adding an accelerant.
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Couldn't you achieve the same thing by advancing ignition timing?