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

Mitianiec W., Zioło T., Noga M.

Journal of KONES

2007

Vol. 14, No. 3

411-421

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.

Study of stratification of CNG mixture in a high charged SI engine

Mitianiec W.

Journal of KONES

2006

Vol. 13, No. 2

323-333

The burning of CNG mixture can occur in very small range of the compression pressure and lean mixture composition. The increased compression pressure requires a big pressure of CNG injection Even for lean mixtures the maximum combustion pressure reaches value near 200 bars. For very lean mixtures and higher compression ratios the misfire occurs, on the other hand for rich mixtures and high compression ratios the detonation is observed. For part load the fuel is injected during the compression stroke, which should form a bigger concentration of fuel near spark plug. The timing of injection should correlate with the piston position BTDC and engine speed in order to enable the adequate stoichiometric mixture near the spark plug during the ignition. The stratification of the charge depends on the location of the injector and the angles of injection nozzles and on the shape of the piston crown. The motion of the injected gaseous fuel required the adequate profile of piston head to turn the fuel stream directly to the spark plug. The flat piston causes that small part of fuel reaches the cylinder cavities and the increase of HC is observed. The paper performs results of calculations of the work engine parameters for 3 types of the piston shapes. The calculations were carried out in the 3-dimensional space with full engine geometry for the same engine speed and injection time. The simulations of CNG injection and combustion process were carried out for motorcycle engine SUZUKI DR-Z400S