COMBUSTION EFFICIENCY OF SPARK IGNITION ENGINES

A simple but accurate model for the combustion efficiency of four-stroke homogeneous charge spark ignition engines has been developed based on thermochemical equilibrium arguments. The model assumes that combustion efficiency is a function of only the fuel-air-equivalence ratio for hydrocarbon fuels with an hydrogen-to-carbon ratio similar to that of iso-octane. This model was shown to accurately predict experimental data for ranges of compression ratio, load, ignition timing, and speed typical of normal engine design and operation. The model slightly overpredicts the data for higher than typical engine speeds and is not applicable to engines operating near the partial burn, ignition, or lean misfire limits. An example of the potential usefulness of this model is also briefly discussed. (TRRL)