Influences of Intake Charge Preparations on HCCI Combustion in a Single Cylinder Engine with Variable Valve Timing and Gasoline Direct Injection 2006-01-3274

Intake charge preparation has strong effects on HCCI combustion, especially on the start of ignition. In this paper, the influence of different intake charge preparation modes on HCCI combustion in a single cylinder engine equipped with a hydraulic variable valve train (VVT) and gasoline direct injection (GDI) system is studied. By using VVT and GDI, three different intake charge preparation modes are implemented: re-compression early injection (RCEI), re-compression split injection (RCSI), and re-breathing early injection (RBEI). For each intake charge preparation mode, three engine operating conditions are investigated: 1.5 bar IMEP at 1000 rpm, 3 bar IMEP at 2000 rpm, and 6 bar/deg of maximum rate of pressure rise at 3000 rpm (IMEP's very near 3 bar). For all engine operating conditions and intake charge preparation modes, the combustion phasing, represented by the 50% mass fraction burned location (CA50), were fixed at 5 degrees after top dead center. The combustion characteristics, engine performance, and emissions are analyzed. It is found that both re-compression split injection and re-breathing early injection modes introduce heterogeneity into the mixture in the combustion chamber leading to higher CO or HC emissions, compared to the re-compression early injection mode. In RCSI mode, local rich combustion introduced by the second injection generates more CO emissions than the RCEI mode. With the second exhaust valve opening during the intake stroke in the RBEI mode, more exhaust gases are introduced into the combustion chamber to dilute the intake charge and lead to more incomplete combustion and more HC emissions than that of the RCEI mode.