Optimization Of Rapid Mixing Combustion System For Diesel Engine At High-altitude

Diesel engine is widely used as a power plant for vehicles due to its better power,safety and reliability.Because of the wide distribution of plateaus in China,it is of great significance to develop high-altitude adaptive power equipment for vehicles.However,the high cold and oxygen-deficient environment of the plateau region pose severe challenges to the performance of diesel engines.For instance,the combustion deterioration and the piston ablative failure of a diesel engine occurred when the engine was working at high altitude.In this context,it is of great practical significance to explore the mechanism of piston ablation in high altitude diesel engines and to give the optimal scheme.In this paper,the influence of high altitude condition and fuel quality on the spray combustion process of diesel engine is studied by using 3d simulation software through the simulation calculation of the constant volume spray and the combustion process in cylinder.The results of constant volume spray simulation show that when the back pressure of the same diesel is the same,the liquid penetration increases as the back pressure decreases.When the back pressure is the same,in the lower temperature range,the spray liquid phase penetration increases with increasing temperature.As the temperature continues to rise,in the later stages of spray development,the development rate of liquid phase penetration decreases with increasing temperature.When the gas-liquid two phases reach equilibrium,the liquid-phase penetration distance decreases with increasing temperature.With the increase of altitude,the liquid spray penetration distance increases under the combined action of ambient temperature and pressure.The spray development process of diesel with different qualities is less affected by the difference in viscosity,density,and surface tension,and is more affected by the evaporation characteristics.Under vaporized conditions,the lower the initial distillation temperature of diesel,the smaller the liquid phase penetration distance when the gas-liquid phase reaches a steady state.The simulation results of the spray combustion process in the cylinder show that under high altitude conditions,the lower temperature and pressure of the intake air in the cylinder cause the delay of ignition and the increase of the spray penetration.The phenomenon of wet wall of fuel oil in the cylinder leads to the deterioration of combustion,the instantaneous heat release rate and pressure increase rate increase,and the amount of carbon smoke increase.The difference of fuel evaporationcharacteristics has a great impact on the ignition delay period.However,since fuel evaporation is an endothermic process and the ignition time is affected by the mixture concentration and temperature,the ignition delay period is not linearly related to fuel evaporation characteristics.Through the design of combustion chamber profile and parameters of oil injection system,the scheme to alleviate combustion deterioration and piston ablation in cylinder at high altitude is obtained.The simulation results show that: compared with the original engine,when the optimized scheme is adopted,the maximum pressure rise rate of the diesel engine at the altitude of 4500 m is reduced significantly,the accumulated carbon smoke production is reduced by 10%,the average temperature in the maximum cylinder is slightly decreased,and the indicated power is slightly increased,the condition of the wet fuel wall is alleviated.At the same time,the thermal load and mechanical impact borne by the piston are reduced,and the probability of piston ablation is reduced.