Numerical Simulation Study On Combustion Process Of Gasoline-fueled Rotary Engine

The rotary engine is a unique engine,and it have some meritive features,like high power density,smooth operation and so on.But the engine's backward is obviously.The flattened combustion chamber of the rotary engine will result in high unburned hydrocarbon emission.Therefore,the study of petrol rotary engine to reduce the exhaust emissions and improve the combustion efficiency is very meaningful.Based on this point,The simulation of 3D rotary engine is established,and the three-dimensional dynamic simulation model is also validated by the experimental data.In this paper,The effects of ignition position,equivalent ratio and hydrogen ratio on the combustion process and performance of the engine were studied.At the same time,the influence of ignition advance angle on combustion process under different working conditions is analyzed,which provides theoretical guidance for rotary engine performance optimization.(1)Base on the structural parameters of the rotary engine,The simplified three-dimensional geometric rotary engine grid modeling is established,which is rotated around the eccentric shaft with UDF program.For better accuracy,a suitable turbulence model(RNG k-? model),combustion model(EDC model)and other model is selected.At the same time,a simplified gasoline simplification mechanism(40 components,69 steps)was added.Then,the grid independence and the model is verified,which proves that the model is reliable.(2)For optimize the defect of the flattened combustion chamber and the unidirectional flow in the combustion chamber,the four kinds of ignition positions is studied.It can be concluded that under the second ignition scheme at the coordinates of(10mm,-56 mm,37.2mm)and(-10 mm,-56 mm,-37.2m),will optimize the rotary engine's combustion efficiency and obtain the maximum power.On the basis of scheme two,the ignition advance angle is studied.It is found that with the increase of the ignition advance angle,the pressure peak is larger and the crank angle of the pressure peak is closer to the top dead center,so the rotary engine's power performance is greater,but the NOx production is higher.(3)The influence of the equivalent ratio on the combustion process and performance is analyzed and the influence of the combustion process of lean burn and rich burn with the change of ignition advance angle is studied.The results are as follows,when equivalent ratio is 0.94,the performance of rotary engine is better and pollutants are less,mainly due to the fast combustion rate and the high efficiency can be get when equivalent ratio is 0.94;In order to improve the efficiency and dynamic performance of the engine under the oxygen-enriched conditions(equivalent ratio of 0.94),the ignition advance angle should be chosen to-42°BTDC.It can be found that in the later combustion stage the rotary engine has little effect on the mass fraction of the burned C8H18 and the mole fraction of the NOx in the cylinder with the change of the ignition advance angle.It was found that the maximum difference between the mass fraction of the burned C8H18 and the mass fraction of the in-cylinder NOx in the later stage of combustion with the change of the ignition advance angle was smaller than that in the case when equivalent ratio is 1;It also can be found that in the later combustion stage has greater impact on the mass fraction of the burned C8H18 and the mass fraction of the NOx in the cylinder with the change of the ignition advance angle.It was found that the maximum difference between the mass fraction of the burned C8H18 and the mass fraction of the in-cylinder NOx in the later stage of combustion with the change of the ignition advance angle was higher than that in the case when equivalent ratio is 1.(4)The effect of hydrogenation rate on the combustion process of gasoline rotary engine was studied.The results are as follows,with the increase of hydrogen mixing ratio,the average pressure &temperature and peak pressure &temperature in cylinder increases.What is more the peak pressure much closer to the TDC.With the increase of the hydrogen mixing ratio,pressure and temperature rise rate and reduce the rate enlarge significantly after reaching peak pressure.NOx formation rate enlarge as the increase of temperature in the cylinder and CO generation rate decreased due to the reduce of hydrocarbons.With the increase of the ignition advance angle,the mass fraction of the burned C8H18 and the mass fraction of NOx in the later combustion stage is increased,and the larger the ignition advance angle is,the more the fuel combustion is more complete and the NOx generated in cylinder more serious than the pure gasoline.