Theoretical and experimental study of the ignition process in CNG direct injection SI engines

The future requirements of CO2 emission decreasing in ICE by applying of new fuels leads also to a design of new engines with direct injection of the compressed natural gas in internal combustion engines with high compression ratio. Because of higher temperature of CNG ignition the SI engines have more effective ignition system than conventional engines. The gas motion, turbulence, charge temperature, spark gap, electrical resistance of the gas and obviously electrical energy of the coil have a big influence on the ignition and burning process in the combustion chamber. The paper includes theoretical and experimental investigations of ignition process in the high charged SI engines with direct CNG injection and in the caloric chamber. The influence of the "tumble" and "swirl" on the sparking is shown by modelling of this process. The paper includes also the thermal efficiency of the ignition process with given values of radiation, conductive and ionization losses. The experimental and mostly simulation tests showed some important factors which influence on the ignition and combustion process of the compressed natural gas. The thermal efficiency of the ignition system increases linearly with the initial pressure in the chamber. The energy consumed by the charge is only a small part of the total energy delivered by the secondary circuit of the coil. The test of the influence of the gas motion on the ignition and combustion process of methane was carried out in CFD environment.