Research On Fluid-solid Coupling Heat Transfer Of Pistons Based On Cycling In Gasoline Engine

In recent years,energy-saving and emission-reduction have been the subject of enginerelated research.The engine is developing in the direction of small displacement and high power.Increasing the compression ratio is one of the main means to increase the engine's effective power.However,the improvement of the compression ratio imposes higher and higher requirements on the performance of engine parts.Moreover,with the increase of the compression ratio,the load of the piston increases correspondingly.Among them,the piston thermal load is the main influencing factor of the piston performance.According to the existing research on the heat of the piston,the thermal boundary conditions of the top surface of the piston are mostly determined by empirical formulas;or the three-dimensional simulation software is used to obtain the top surface heat transfer coefficient of the piston and the temperature in the cylinder,and the sequential fluidstructure coupling method is used to solve the problem.In this paper,the direct fluidstructure coupling method is used to calculate the piston temperature field.This method considers the environment in the cylinder and makes the simulation more in line with the actual situation.This article is based on the Honda 125 motorcycle carburetor engine with a compression ratio of 9 and will be transformed into an engine with intake port injection as the research object.A one-dimensional model of the original machine was built using onedimensional commercial software of the engine,and it was verified by a bench test.The boundary conditions of engine piston heat transfer are set according to the one-dimensional model simulation results and empirical formulas.Using CATIA to establish a piston model with a compression ratio of 9 and using a finite element method to determine the piston temperature field at 4000 r/min and 100% throttle opening conditions.This method calculates the symmetrical distribution of the piston temperature field.Using CATIA to build the engine model,including the original piston with a compression ratio of 9 mentioned above,the boundary condition of the piston side is consistent with the conditions used in the finite element calculation method.The direct fluid-structure interaction heat transfer method was used to find the piston temperature field under the above conditions.It was found that the top surface temperature of the piston was asymmetric,and the spatial distribution of the heat transfer coefficient of the top surface of the piston under different crankshaft rotations was obtained.And the overall piston temperature is consistent with the finite element calculation results.By modifying the top profile of the piston of the original machine,the finite element method was used to analyze the heat transfer characteristics of the temperature field in the flat top piston with compression ratio of 12 and the piston with channelized pits.According to the in-cylinder pressure simulation data,the detonation phenomenon occurred in this type of piston.By changing the injection mode to direct injection in the cylinder,no deflagration phenomenon was found.The direct fluid-solid coupling heat transfer method was used to simulate the spatial distribution of the temperature field at the top-level piston and the instantaneous heat transfer coefficient at the top surface.