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The main objective of this paper is to investigate the influence of injection pressures and fuel temperatures on the secondary injection spray evolution at the end of injection from a multi-hole gasoline direct injection (GDI) injector by Mie-scattering technique. The results of this paper show that the overall injection process can be classified into five stages which are injection delay stage, main injection stage, dwell stage, secondary injection stage and ligaments breakup stage respectively. Especially, the secondary injection occurs at the end of main injection, which is abnormal and undesirable spray behaviors. During the injection, big droplets and ligaments are injected through nozzle orifices at low speed. As the injection pressure increases, the phase of the secondary injection advances, and the injection duration decreases. At medium injection pressures (at 6, 8 MPa), more quantity of fuel are injected as ligaments.

The effects of exhaust gas recirculation (EGR), late intake valve closure (LIVC) and high compression ratio (HCR) on the performance of a 1.6L multi-point injection (MPI) gasoline engine at 2000rpmwere investigated in this paper. Compared to the baseline engine, The improvement of fuel consumption is about 1.4%∼4.5% by using EGR only because of a reduction of pumping loss(PMEP). Nevertheless deterioration of combustion is introduced at the same time for high specific heat of EGR. The maximum EGR rate introduced in this system is limited by cyclic variations of indicate mean effective pressure (COVIMEP) at low load and fresh charge to achieve enough output power at high load. After combined LIVC and HCR, the improvement of fuel consumption is about 3.5%∼9.6% compared with the baseline engine at the same operation conditions because of significant PMEP reduction, increasing of effective compression ratio (ECR).