Sensitivity of Pressure Rise to Spark Energy and Flame Travel Velocity in a Spark Ignition Engine

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. Additionally, an appreciable change of rate of pressure rise during glow and arc discharge modes was predicted with changes in spark energy. This was confirmed experimentally.