Analytical Investigation of Cam Strategies for SI Engine Part Load Operation

Extensive simulation was carried out to investigate cam strategies for SI engine part load operation. Performance of the engine with dual independent variable cam timing (VCT) system is assessed. Over a wide range of part load operating conditions, engine performance parameters, such as fuel consumption, were expressed in forms of contour maps as a function of intake and exhaust cam timings. Based upon the simulation results, cam timings were optimized for various part load conditions. A cam strategy incorporating intake and exhaust cam retard was developed to improve fuel economy and emissions. Influences of intake and exhaust cam timing on the gas-exchange and combustion processes were also analyzed. It was shown that the fuel economy improvement by dual independent VCT is achieved primarily through reduction of pumping loss. Effects of in-cylinder charge motion and the use of differential intake cam profiles on fuel economy were examined. The simulation was compared with the experimental data from a single cylinder engine. Good agreement between the prediction and the measurement was observed for most performance parameters interested. Therefore, the simulation provided useful information for understanding of the engine thermodynamic process and guidelines for engine combustion system development.