Study On The Influence Of Piston Shape On Combustion Of Different Compression Ratio Engine

As the main power source of passenger car, the ignition conditions and combustion mode of gasoline engine are the key factors influence combustion quality and engine performance. As the high-speed moving part in combustion chamber, piston carries the boundary conditions and initial conditions during the engine running. The shape of piston top has important influence on the fluid flow and combustion process in the cylinder. In this paper, aimed at improving the comprehensive performance of the engine, the simulation software AVL FIRE was used to simulate the gas flow and combustion process of an intake port injection gasoline engine.In this paper, the modeling process and numerical calculation method was discussed, the gas flow conservation equation, the turbulence model and combustion model of gas inside the cylinder were introduced. Based on the point-cloud of the intake and exhaust port and combustion chamber of engine Honda WH125-6, the modeling software CATIA was used to reverse surface, the grid pretreatment software Hypermesh is applied to generate surface grid model. The initial conditions and boundary conditions for three-dimensional numerical simulation were concluded through the one dimensional performance simulation software BOOST. AVL FIRE was used to simulate the engine cycle of maximum torque working condition at 4000 r/min. By comparing the simulation results and the results of bench test, the simulation model was calibrated to verify the accuracy of the model and the rationality of parameter settings.A series of piston models with the compression ratio of 10, 11, and 12 were built, the software FIRE was used to carried out numerical simulation of each combustion chamber, and the flow field and combustion process in every engine combustion chamber were analyzed in detail. By comparing the performance of different schemes, it could be obtained that when improving engine compression ratio, reasonable design of the top part of piston is beneficial to the whole engine performance. Among them, with both the spark plug vortex and the canalization structure on the top of the piston, the scheme of compression ratio of 12 performed well. The research results showed that the reasonable design of piston shape will improve the engine compression ratio, as well as the organization and the gas flow field in cylinder combustion process.