Numerical Simulation On Mixture Formation And Combustion Of Opposite Piston Diesel Engine

The numerical simulation method was applied to explore the optimization of the emission performance of an opposed piston opposed cylinder(OPOC)diesel engine,and a arrangements of group hole nozzles was proposed to improve the combustion and mixture formation of the OPOC diesel engine.The main contents were as follows:Firstly,the composition and working principle of the OPOC diesel engine were briefly described.Analyzing the piston motion law to obtain the motion curve of the inner and outer pistons.The three dimensional model of the OPOC diesel engine combustion chamber was carried out,and AVL fire software was employed to establish the numerical simulation model of an OPOC engine.The physical model applied was described;determining the initial value and the boundary condition,and verified the simulation model.Secondly,using three optimization algorithms,the optimal emission of OPOC diesel engine was optimized by matching the fuel injection starting point,the orifice diameter and the fuel injection duration under the condition that the maximum burst pressure in the cylinder is between 11 and 15 MPa.performance.The influence of three parameters on the emissions of OPOC diesel engine was compared and analyzed.The results showed that delayed injection can inhibit premixed combustion and reduce NO emissions.Reducing the orifice diameter and shortening the injection duration can increase the injection pressure,which is beneficial to improve the quality of the mixture and accelerate the rate of heat release.However,the smaller orifice diameter has a negative effect on the spatial distribution of the fuel.Meanwhile,shortening the injection time not only facilitates the formation of the mixture,but also shortens the afterburning period and reduces the in-cylinder combustion rate and temperature.Integrated engine performance and emissions performance to obtain an optimal solution.Finally,a novel fuel injector with converging group-hole nozzles which were arranged in circumferential direction was proposed.Three arrangements of converging group hole nozzle were designed,and without modifying the injection pressure,the fuel spray,mixture formation and combustion process of a model OPOC diesel engine were analyzed.The results indicated that compared with the conventional nozzle,the converging group-hole nozzles has less influence on the spray penetration distance,and the fuel distribution of the group-hole nozzle is more uniform,which is beneficial to improve the mixture formation and obtain higher in-cylinder pressure and combustion efficiency.Appropriately increasing the converging angle is beneficial to the improvement of the cycle thermal efficiency and reducing the emission of soot;the reasonable nozzle hole arrangement can greatly improve the quality of the mixture formation in the lower nozzle of the single nozzle,and reduce the soot emission;the increase of converging angle,the difference in the distribution of the spray and the combustion performance of the different groups of nozzle arrangement is smaller.