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 (PRRmax) 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, PRRmax
was found to increase with increasing supercharge pressure. It was determined
that the PRRmax in the fully homogeneous mode was higher than in the
early direct injection condition. At low MAP values, the difference in
PRRmax 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.
