Simulation Study On Air Flow And Combustion Process In Highly Intensified Diesel Engine

Highly intensified diesel engine has the characteristics of high speed,large amount of incylinder air and high fuel injection pressure.It can meet the development requirements of diesel engine with compact structure,strong power,and efficient performance,but at the same time,it puts forward higher requirements for the air flow in the cylinder,the mixing of fuel and gas,and the combustion process.In the intake stroke,a reasonable intake port structure can ensure sufficient air intake and good airflow movement,thereby improving the performance of the highly intensified diesel engine;in the compression and combustion stroke,the structure of the combustion chamber will have an important impact on the mixing of fuel and gas and the combustion process.Therefore,it is of great significance to analyze the flow field states of the intake port and the cylinder during the working process of the highly intensified diesel engine,as well as the influence of different intake port structures and combustion chamber shapes on its air flow,fuel-gas mixing,and combustion performance.First of all,this paper takes a certain type of highly intensified diesel engine as the research object,and uses the 3D simulation software Converge to simulate its working process.The corresponding three-dimensional mathematical model of the high-strength diesel engine is selected,and the initial parameters and boundary conditions required for calculation are specified.The results are compared with the data measured on the single-cylinder experimental platform to ensure the accuracy of the simulation model and parameter settings,and the flow field changes of the intake-compression-combustion stroke in the cylinder are analyzed in detail.Secondly,based on the original model,this paper selects a new type of inlet structure with a helical port and a tangential port,analyzes the airway flow characteristics of the combined inlet,and focuses on the velocity at the valve clearance.then the effects of different intake port structures on the in-cylinder flow field and combustion characteristics were compared and studied.The results show that although the combined intake port slightly reduces the cumulative intake air volume in the cylinder,it greatly improves the vortex ratio in the cylinder and always maintains a certain intensity,which promotes the fuel-gas mixing and combustion reaction at the end of the compression stroke.Finally,this paper established two combustion chambers with different structures by changing the diameter-to-depth ratio of the combustion chambers.Characteristic parameters that quantitatively characterize the mixing of fuel and gas and combustion performance were selected,and combining the three-dimensional flow field distribution state,the influence of different combustion chamber diameter-depth ratios on the fuel-air mixing and combustion heat release of the highly intensified diesel engine was studied in depth.The results show that appropriately reducing the diameter-depth ratio on the basis of the original combustion chamber model can enhance squeeze flow and reverse squeeze flow and promote the mixing of fuel and gas in the cylinder,thereby improving the combustion process and the power of the diesel engine.