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The significance of the relative effects of the spark energy, the flame travel velocity around the spark plug, and the heat loss to the spark plug on the cylinder pressure development was studied. An one dimensional fluid dynamic model of flame initiation during spark breakdown was developed to determine initial flame kernel size. A thermodynamic model for the subsequent flame growth process during the arc and glow discharge processes was also developed to model the flame propagation and pressure rise. Overall reaction rates, flame speeds including turbulence and intensity, high temperature equilibrium and other thermodynamic properties were calculated by peripheral submodels. Relative effects of spark energy, heat loss to the spark plug and flame travel velocity were studied. Results show that the sensitiveness of the cylinder pressure to spark energy and flame kernel travel velocity on subsequent combustion was considerable at specific engine conditions.

A thermodynamical model of the ignition and flame growth process was developed to understand and minimize cycle-to-cycle variations in pressure due to minor differences in flame kernel growth at the spark plug electrode between cycles. Initial flame kernel size after the spark breakdown process was determined by solving the one-dimensional cylindrical shock flow equation. Overall reaction rates, flame speeds including turbulence and intensity, high temperature equilibrium and other thermodynamic properties were calculated by peripheral sub-models. Relative effects of spark power, heat loss to the spark plug, and the chemical heat release were studied under varying engine conditions. Results show that breakdown energy has a significant effect on the formation and size of the initial kernel and that the effect of flame kernel velocity on subsequent combustion was considerable at specific engine conditions.