Abstract: A DMS500 fast particulate spectrometer was employed to explore the particle emissions characteristics of a dual-injection gasoline engine. The main goal is to investigate the effects of operating conditions (speed and load ) and direct injection timings on the particle size distributions and particulate emissions in steady state conditions. The experimental results indicate that the combustion characteristics of dual-injection are similar to that of the direct-injection mode at low loads. While at middle and high loads, the peak of in-cylinder pressure curve of dual-injection is a little higher than that of the direct-injection mode. Dual-injection yields great particulate emissions reduction. As the speed and load rise, the particulate emissions of dual-injection gradually increase. At middle and high loads, the particulate emission improvement of dual-injection with 50% fuel directly injected declines significantly. Compared to the direct-injection mode, the particle size distributions of dual-injection tend to shift towards the smaller size region. There exists the best injection timing for the direct-injection mode to yield the lowest particulate emissions. For the dual-injection mode, the best direct injection timing is much closer to the exhaust top dead center than that of the direct-injection mode.

Key words: direct-injection, dual-injection gasoline engine, particulate emissions, particle size distribution, direct-injection timing