Modeling Of Two-Stroke GDI Engine And Simulating Of Fuel-Air Mixture Formation

It is difficult to meet the requirements of the engine power performance and fuel economy for two-stroke PFI(Port Fuel Injection)gasoline engine,due to the simple mechanical structure of two-stroke engine making it poor fuel economy and high emissions.The GDI(Gasoline direct injection)engine can reduce or even avoid short-circuit loss of fuel,and can control fuel injection strategy flexibly to optimize the performance of the various operating conditions,and the defect of ventilation aspect can be made up.The fuel efficiency can be greatly improved and emissions can be reduced by GDI.In this paper,the PFI model and GDI chamber was built by CFD-Fluent.Using the chamber the influence of injection parameters on the mixture were studied.And the influence of altitude on the mixture and fuel loss was studied.In this paper,the main research content and the main innovation is as follows:(1)The simulation model was established and verified by GT-power according to the engine structure parameters and operation parameters,in order to providing CFD-Fluent model with boundary and initial conditions.(2)With the airway size and location invariable,two different combustion chambers were designed,the distribution of flow field velocity distribution,the exhaust gas flow field and the scavenging efficiency were analyzed to estimate new chamber feasibility.(3)The original engine chamber was changed to study the flow field in the cylinder and the fuel distribution.The research showed that: It is not easy to form a stratified mixture combustion and roll uniform flow in cylinder at low load condition with the original engine chamber.These unfavorable conditions can cause the accumulation of fuel,the incomplete combustion and high emission.So,it is necessary to design new combustion chamber;Using the best combustion model,at low load condition(1500 r/min,the throttle position 10%),the influence of fuel injection parameters on the layered dilute mixture formation process was simulated,the injection timing,the direction of injection and injection pressure inside the cylinder velocity vector,the influence law of turbulent kinetic energy and the fuel distribution in cylinder were analyzed.Research shows that: in the guarantee of fuel to diffusion,select the appropriate fuel injection angle,bigger injection pressure,and the spray angle is 15 ° and injection timing at 70 ° CA ~ 90 ° CA help stratified mixture formation.At the same time,at high load condition(5000 r/min,the throttle position 100%),fuel injection parameters on the formation process of homogeneous mixture was simulated,the influence of injection timing,the direction of injection and injection pressure inside the cylinder velocity vector,the influence law of distribution of turbulent kinetic energy and fuel in the cylinder were analyzed,the research showed that: in the guarantee of the mixture evenly and reduce fuel escape,while injecting advance as far as possible and increasing the injection pressure,the more uniform distribution of fuel in cylinder,the fuel injection angle is 15 ° and injection timing at 200 °CA ~ 220 ° CA contribute to the formation of homogeneous mixture.(4)Under the condition of 5MPa fuel injection pressure,15° fuel injection angle,the influence of altitude(0 m,1500 m and 3000 m)on the flow field in cylinder and scavenging air condition and fuel loss at high load condition(5000 r/min,the throttle position100%)was studied using the established simulation model,and the influence of injection timing(180 CA,200 CA,220 CA,240 CA BTDC)on the flow field in cylinder,the fuel distribution and fuel loss were studied.Research showed that: with the altitude increasing,the influence of fuel injection on the flow field in the cylinder is more and more strength,because of the low velocity of flow in cylinder and weak cylinder rolling flow intensity,the time of fuel to exhaust port is longer,the loss of the fuel short circuit and fuel loss reduce.