Gasoline direct injection into a four-stroke engine to investigate the effect of injection timing on mixture formation and combustion

Energy crisis is one of the crises which human beings face these days. Optimizing the operation of energy consuming machines is one of the most effective methods in decreasing energy consumption. Gasoline direct injection engines as new achievements in automobile and propulsion industry, reduce fuel consumption by increasing the engine efficiency. In these types of engines, a high pressure injector injects fuel directly into the combustion chamber instead of injecting fuel in intake ports. Thus, because of evaporation cooling, the mixture cools down, so the possibility of achieving higher compression ratios in higher engine speeds and loads, without occurrence of knock is provided. Increase of compression ratio increases the engine thermal efficiency. In low speeds and loads, by removing throttling valve and creating stratified mixture fuel consumption is reduced. In this research, using AVL Fire code dynamic mesh of National engine chamber was generated and air entering the chamber was simulated. Then, a fuel spray emerging from a high pressure 6-hole injector was used to inject fuel directly into the chamber and form the air-fuel mixture. Spark and combustion were modeled by spherical and ECFM model, respectively. Finally, the effect of delay in start of injection time on the combustion was investigated. Combustion simulation results show that in case of forming stoichiometric mixture, fuel should be injected early to create homogenous mixture and mixture combustion becomes complete. Late injection of fuel causes inappropriate mixing of fuel and air, spray-wall impingement, fuel wall-film and so incomplete mixture combustion. As a result, power production is reduced and emission formation increases