Numerical Investigation on the Effect of Fuel Temperature on Spray Collapse and Mixture Formation Characteristics in GDI Engines 2018-01-0311

Spray atomization, spray-wall impingement, and mixture formation are key factors in affecting the particulate matter (PM) emission in gasoline direct injection (GDI) engines. Current knowledge of wall-wetting phenomenon and mixture formation are mostly based on the studies that the fuel is injected at ordinary temperature and various ambient conditions. In the real GDI engine, the fuel pipe and injector are always heated up by the pump and the engine body, especially at hot engine conditions, thus the fuel temperature is always higher than the ordinary temperature, and the relevant research is still limited. The aim of this study is to numerically investigate the spray, spray-wall impingement, and mixture formation characteristics under different fuel temperature conditions, so as to provide theoretical support in optimizing the combustion performance and further reducing the PM emission of GDI engines. The spray model is calibrated with the high-speed imaging and PDPA (Phase Doppler Particle Analyzer) experiments. The results show that increasing the fuel temperature leads to a collapse of the spray plumes and decreases the spray penetration length. At the same time, the impinged fuel area, propagation length, and the fuel film mass are also reduced by the better spray atomization, quicker evaporation and less deposited fuel. The proportion of high fuel concentration near the impact surface is also reduced by increasing fuel temperature. The increase of fuel temperature is believed to be an effective and practical way to optimize the spray atomization, alleviate the adverse effects of impingement, and accelerate the mixture formation process in GDI engines.