Comparison of Combustion Parameters and Homogeneity of Full and Direct Injection Homogeneous Charge Compression Ignition Engine under Supercharger Conditions

In this study, a numerical model validation of the supercharged homogeneous charge compression ignition (HCCI) engine, whose experimental studies at 100, 110, 120, 130, 140, 150, and 160 kPa pressures, was carried out using Converge CFD program. After validation, the in-cylinder pressure, heat release rate (HRR), and maximum pressure rise rate (PRR_max) of a fully HCCI engine and an early direct injection HCCI engine were compared numerically at different supercharger pressures. According to the comparison results, it was observed that the cylinder pressure increased and the maximum in-cylinder pressure point advanced with the increase of the supercharge pressure in the fully homogeneous and early direct injection mode. In the early direct injection system, it was observed that the maximum pressure was lower than the results obtained in fully homogeneous conditions, especially at high manifold absolute pressure (MAP) values. In both modes, it was determined that with increasing supercharger pressure, HRR increased and the maximum HRR point advanced. A wider HRR curve is obtained in the early direct injection mode. In both cases, PRR_max was found to increase with increasing supercharge pressure. It was determined that the PRR_max in the fully homogeneous mode was higher than in the early direct injection condition. At low MAP values, the difference in PRR_max value between a fully homogeneous mixture and early direct injection is low, but this difference gradually increased with the increase in MAP. As a result of the analysis, the heterogeneous air-fuel mixture is formed due to the fuel injected into the cylinder in the early direct injection HCCI mode. In early direct injection HCCI mode, the more heterogeneous filling is obtained by spraying the fuel into the air in the cylinder. It is seen that almost all of the mass fraction has the same equivalence ratio until the fuel injection starts and there is an inhomogeneous mixture after fuel injection in the early direct injection HCCI mode.