Abstract:   A DMS500 fast particulate spectrometer was employed to characterize the particle size distribution for a naturally aspirated gasoline direct injection (GDI) engine. The goal is to investigate the impact of engine operating parameters (load condition, coolant temperature, spark timing), injection strategies (start of injection, fuel pressure) on particulate size distribution and particle number, and thermogravimetric analyses of particulate matters in different load conditions.The experimental results show that, particulate size distribution is bimodal in form with nucleation mode particle and accumulation mode particle, depending on nucleation mode at low load or accumulation mode at high load. Cold coolant temperature produces higher particulate matter emission. With delay of spark timing, the particle number is reduced. An optimized injection timing valve has been found based on operation conditions. Fuel pressure has a significant effect in particle number, high fuel pressure reduces particle number and increases nucleation mode percentage. With increases of load, and decrease of coolant temperature, the maximum mass loss rate temperature of soot increases and soot oxidation activity reduces.

Key words:  gasoline direct injection (GDI) engine; injection strategy; particle number; size distribution; thermogravimetric analysis