Effects of Spark Timing with Other Engine Operating Parameters on the Particulate Emissions of a Dualinjection Gasoline Engine During Warm-up Conditions

Gasoline direct injection (GDI) has been a mainstream technology due to its higher thermal efficiency and better power output. However, with increasingly stringent emission regulations introduced (EURO VI PN limits: 6 x l0¹¹#/km), high particulate matter (PM) emission of GDI engine has been a serious problem that limits its further development. Previous studies have found that cold-start and warm-up operation conditions play the dominant role in engine-out particulate emissions. In this paper, emission characteristics during the cold-start were first studied by controlling the coolant temperature. A Cambustion DMS500 fast particle spectrometer was employed to analyze the PM emissions. In order to reduce the engine-out emissions of cold-start, a dual injection system which combines port-fuel-injection (PFI) and direct-injection (DI) was applied in a four-cylinder gasoline engine. After that, this research mainly investigated the influences of spark timing on the engine-out emissions under constant DI injection ratio. The results indicated that with application of dual injection system, total PN emissions had decreased significantly by up to an order of magnitude compared with GDI engine, while the size distributions of both were similar, featured as bi-modal-shaped. As for the impacts of spark timing, it was observed that total PN emissions would decline with the delay of spark timing, as well as a notable reduction in the GMD. Besides, the proportion of PN in nucleation mode showed a trend to increase with the delay of spark. The experimental results obtained above may provide a new technical roadmap for PN emission reductions during warm up periods in the future GDI engines.