A Numerical Study On Air-fuel Mixture Formation And Combustion Process Of High-speed Gasoline Engine

The more stringent regulation on motorcycle pollutant emissions has been promulgated,which put forward new requirements on the motorcycle gasoline engine fuel supply system and the organization of the combustion process.Now most of the motorcycle gasoline engine use electronic fuel injection technology,and mainly for port-fuel-injection(PFI).However,the motorcycle engine’s small intake-port and high speed are limitation for learning from the more mature vehicle engine PFI technology,Therefore,it is of great theoretical and practical value to study how to improve the formation quality of the air-fuel mixture in cylinder and the effective organization of the combustion process.In this paper,CONVERGE software is used to study the process of air-fuel mixture formation and the combustion process.Firstly,the intake-port performance is analyzed by air flow rig test,and the intake-port CFD model is calibrated against air flow rig test data.The next,the fuel spray characteristics of each injector are analyzed by schlieren method which takes in a constant volume combustion bomb,and the numerical model is verified by photographing pictures and data.Then,the influence of the injection parameters on the air-fuel mixture formation in the cylinder is studied.The numerical simulation is carried out from the injector type,the fuel injection angle,the fuel injection time and the secondary injection respectively,and explored how to reduce wall-film and form more homogeneous mixture of full-load at high speed.The results show that:1)The more number of injectors and the smaller diameter of the nozzle can reduce wall-fuel and improve the equivalence ratio in cylinder.2)Changing the fuel injection angle has a great impact on the distribution of the equivalence ratio of the cylinder and the formation of wall-film.The injection point at the junction of intake-port and intake valve makes the lower quality of wall-film and higher equivalence ratio in cylinder.3)Semi-open valve injection mode makes higher equivalence ratio in cylinder,but closed valve injection mode has more homogeneous mixture of air-fuel.4)When the engine at high speed of full load,secondary injection has no advantage compared with single injection because of the higher body temperature and larger air flow.Finally,the effects of different operating parameters such as equivalence ratio,ignition parameter,compression ratio and the rate of EGR(Exhaust Gas Recirculation)on the combustion process are studied at high speed,which provide theoretical basis for more efficient and lower emission combustion system.