Effect of swirl on performance and emissions of CI engine in HCCI mode

Abstract

A promising combustion strategy that combines the advantages of both SI and CI combustion modes is the homogeneous charge compression ignition (HCCI) combustion mode. A volumetric combustion of a lean mixture of charge is the advantage of HCCI combustion, leading to low NOx emissions and soot. In this work, HCCI combustion mode is analyzed to study the effect of swirl motion of intake charge on performance and emissions of the engine using a Three-Zone Extended Coherent Flame Combustion Model (ECFM-3Z, Compression Ignition). The present study revealed that ECFM-3Z of STAR-CD predicts well the in-cylinder pressures, temperatures, cylinder wall heat transfer losses, piston work and emissions such as CO, CO2 and NOx of the CI engine in the HCCI mode. The ECFM-3Z model has a predicted variation in turbulent kinetic energy and velocity magnitudes inside the cylinder during combustion, facilitating better understanding of the combustion process. The simulation results show that the there is a reduction in in-cylinder peak pressures and temperatures, as the swirl increases and CO emissions increase because of reduced temperatures, and CO2 and NOx emissions decrease because of the reduced in-cylinder temperatures. It is found that there is a trade-off between the emissions and piston work. Higher turbulent energy and velocity magnitude levels are obtained with increase in swirl, indicating efficient combustion without a demanding combustion chamber design.