Design And Optimization Of Intake System In A Rotary Engine

As a type of the internal combustion engine,the rotary engines have some advantages,such as high power density,high power to weight,etc.However,the flattened structure of the combustion chamber is adverse to flame propagation,which results in poor fuel economy and high emissions performance.Therefore,the study of how to improve combustion efficiency of rotary engines is very significant.It is a complicated pulsation and resonance process of the engine intake process,which not only has an important influence on the atomization and evaporation of fuel,but also effects the mixtures formation and combustion processes.Based on this point,a CFD model for gasoline Wankel rotary engine was established by using CONVERGE code,and this model had been validated by the experimental results.The flow field,flame propagation,and emissions formation of the rotary engine had been studied.Therefore,the intake structure of rotary engines was designed under partial load conditions and the relevant calculation results provided a theoretical guidance for the optimization of rotary engines.The influence of different inlet-ported structures on the flow field of the rotary engine was studied comparatively.Results showed that different inlet-ported structures led to the pronounced difference in the flow field,for side–ported rotary engines,the intake flow entered rotor housing and impinged on the lower cylinder wall in the intake stroke.After the impaction,two tumbles which the rotation center paralleled to the wall of the combustion chamber were formed.In peripheral-ported rotary engines,the unidirectional flow with rotor movement was formed in the front of the combustion chamber.The mixture at the rear end of the combustion chamber formed a tumble because of the squeezed by the combustion chamber wall and the inlet flow.In the combination-ported structure,the flow field in the combustion chamber was complicated due to the mutual interference of the airflow.Compared with the side-ported rotary engine,the vortex dissipation of peripheral-ported and combination-ported rotary engines were faster,thereby forming an earlier mainstream flow field to accelerate the velocity of mixture formation and combustion.Therefore,the production of OH in the peripheral-ported and combination-ported engines increased by 17.75%and 15.64%,respectively.At the same time,due to the enlargement of the combination-ported rotary engine’s intake area,the coefficient and the peak in-cylinder pressure obviously increased.Compared with the side-ported and peripheral-ported rotary engine,the coefficient of combination-ported rotary engine increased by 11.31%and 5.16%,and the peak in-cylinder pressure increased by5.89%and 2.72%,respectively.It can be seen that the performance of the rotary engine improved effectively by using the combination-ported intake method.The flow field,combustion process and major emissions formation of rotary engines with different side-ported angles was numerically studied.Results found that,with the increase of the side-ported angle,the impinge location of the mixture moved to the front of the combustion chamber and the radius of the vortex was increased.With the inlet angle increased to 30°,the mixture formed a vortex at the rear end of the combustion chamber.The mixture velocity in the cylinder is accelerated with the increase of the inlet Angle,which is conducive to the combustion reaction.Compared with the side-ported angle of 0°,when the side inlet angle increased to 60°,the peak in-cylinder pressure increased by 7.44%,the hydrocarbon and carbon monoxide notably reduced by 25.49%and 26.91%,respectively,though nitric oxides emissions increased by 27.67%.Therefore,the rotary engine obtains a better performance when the side-ported intake angle is 60°.Five different peripheral intake shapes were compared to investigate the influence of intake shape on the flow field and combustion process of combination-ported rotary engines with the side-ported angle of 60°.When adopting the circular intake shape,more mixture entered the combustion chamber at the initial stage of the intake stroke which is beneficial for reducing the mass of residual exhaust gas.It also could decrease back flow phenomenon at the end stage of the intake stroke,thus increase the volume coefficient of rotary engines.It can be concluded that turbulent kinetic energy at the spark timing of the triangle intake design exhibited a26.91%increase compared with the circle intake design,the peak in-cylinder pressure and temperature increased by 5.87%and 2.12%,respectively.However,higher combustion temperature resulted in the increase of NO_xgenerations.In conclusion,it is found that the combustion and emission performances of the rotory engine can be improved by using the combination-ported intake with the side-ported intake angle of60°and triangular peripheral inlet.