Pre combustion energy release and its effect on flame propagation and exhaust emissions in a spark ignition engine

Abstract

The extents of pre combustion reaction and cumulative pre combustion energy release have been computed for various operating conditions in a single cylinder variable compression ratio research engine. Exhaust emission levels of CO and HC are measured by gas chromatography. The mean turbulent flame propagation velocity is estimated from a thermodynamic analysis of the engine cylinder pressure trace. The effect of pre combustion energy release on the flame velocity and the exhaust emissions of CO and HC has been discussed. It is found that the pre combustion energy release may account for as much as 20% of the heat in the fuel in the case of reactive fuels of relatively low octane numbers. In general, increased pre combustion reactivity is found to decrease CO and HC emission levels. However, its effect on the mean engine flame velocity does not appear to be pronounced.The extents of pre-combustion reaction and cumulative pre-combustion energy release have been computed for various operating conditions in a single cylinder variable compression ratio research engine. Exhaust emission levels of CO and HC are measured by gas chromatography. The mean turbulent flame propagation velocity is estimated from a thermodynamic analysis of the engine cylinder pressure trace. The effect of pre-combustion energy release on the flame velocity and the exhaust emissions of CO and HC has been discussed. It is found that the pre-combustion energy release may account for as much as 20% of the heat in the fuel in the case of reactive fuels of relatively low octane numbers. In general, increased pre-combustion reactivity is found to decrease CO and HC emission levels. However, its effect on the mean engine flame velocity does not appear to be pronounced.