Research Of The Improvement Of Intake Port And Combustion Chamber Of Gasoline Engine Based On CFD

The key factors affecting engine performance include the shape of the intake system and combustion chamber as the two have a direct impact over the processes of air intake, fuel atomization and combustion. Rational shape design of the intake system and combustion chamber can improve engine performance and reduce carbon dioxide emissions effectively. CFD has become an important means of engine design and development as it shortens the cycle of engine design and reduces the cost of engine design in an effective way.Based on the tests of gasoline engine performance and the steady flow, a three-dimensional modeling was conducted for the intake port of the original engine by UG software in this paper. A steady-state simulation was also implemented by the three-dimensional software FIRE. After verifying the accuracy of three-dimensional steady-state simulation, deficiencies existing in the original engine intake port were analyzed based on the results of steady flow field simulation, flow coefficient, tumble ratio and other evaluation parameters of the steady flow test. It was found that the original engine intake port had problems of low tumble ratio(against average tumble ratio of 0.73) and insufficient tumble intensity, resulting in slow combustion rate of the original engine. A variety of intake port optimizing plans was proposed accordingly. Steady-state simulation for the optimized intake ports were made and compared to the original engine. Result showed that the average tumble ratio of intake port B1 increased to 0.804 with a slight increase in flow coefficient; the average tumble ratio of intake port B2, B3 and B4 reached above 0.849 with a significant decrease in the flow coefficient.After that, transient numerical of original engine simulation was made. The reason for the inadequate performance at 3000 rpm of the original engine and its excessive fuel consumption lay in the slow burning rate caused by lack of turbulent kinetic energy in the cylinder, which was determined by analyzing turbulent kinetic energy, flow field, temperature field, and the flame developing period, rapid combustion period, peak cylinder pressure and corresponding crank angle, and other parameters of combustion characteristics of the original engine, then proposing the optimizing method for combustion chamber to improve the squeezing effect of piston over gas mixture in the cylinder.Finally, the influence of different models on parameters of engine combustion characteristics was studied by numerical simulation over all the combinations of optimized intake port and combustion chamber. The impact of different combinations of intake port and combustion chamber on turbulent kinetic energy, flow state of gas and combustion process at ignition was shown in details, underlining the analysis of the impact on burn rate, in-cylinder flow field and temperature and making an in-depth discussion over the relationship between turbulent kinetic energy and burning duration. The results showed all the methods of modifications proposed at the speed of 3000 rpm for the defects of the intake port in the original engine were effective and feasible, meeting the optimization goal to optimize the burn rate; but the performance of the optimized top piston surface differed in different intake ports. Optimization methods meeting different requirements were proposed taking account of the simulation results at the speed of 1000 rpm and 5000rpm; as for model B4P1 and B4P2 that meet the low-speed requirement, model B4P1 had a better optimization over the low speed, while model B4P2 was compatible with the high speed; 2, as for model B2P1 and B3P2 that meet the high-speed requirement, model B3P2 had a better optimization over the high speed, while model B2P1 was compatible with the low speed.