Research On Combustion And Emission Characteristics Of Diesel Engine Based On EGR Ring Stratification In Cylinder

The flow characteristics of the diesel engine’s air passage-cylinder have a great influence on the intake mass flow into the cylinder,the gas movement status and the distribution range.In this paper,based on the airway steady flow test combined with CFD simulation,Analyze the movement and distribution of airflow in the cylinder and the stratified combustion of the gas in the cylinder.According to the different valve flow characteristics of diesel engines,the results show:Under low valve opening conditions,too small valve opening will significantly affect the intake air flow,making it difficult to take advantage of the different valves.Different valve strategies It must be designed around the maximum opening of the valve.The use of the appropriate proportion of different valves can significantly enhance the swirl ratio and also promote the intake air volume.Under the same low valve lift condition,due to the smaller opening of the spiral/tangential air intake valve,the air flow through the spiral air passage and the tangential air passage face each other in the cylinder,making the swirl ratio and flow rate The coefficients are difficult to increase;with the increase of the opening of the two valves,the airflow of the spiral air passage will excessively invade the flow field of the airflow of the tangential air passage in the cylinder,causing serious intake interference,resulting in intake energy The loss further limits the improvement of the flow coefficient and vortex ratio.The proper different valves can make the air flow of the dual intake ports make full use of the space in the cylinder,forming interleaved flows in the cylinder,avoiding serious interference of the air flow between the dual air ports,reducing the energy loss of gas movement,and improving the vortex ratio and the purpose of the flow coefficient.Corresponding relationship between the flow field of the cylinder near the wall surface and the thread motion under the condition of different valve lifts of the helical/tangential air passages.Under the two motion states,the air flow from the helical/tangential air passages into the cylinder basically exhibits similar motion laws.The research on the control strategy of the different valve of the diesel engine shows that:the different valve designed around the maximum valve opening of the spiral valve,the tangential valve opening of the valve is greater than or equal to 2/3 of the maximum valve lift can be significantly enhanced when designing In addition,it also promotes the intake air volume.Different valves designed around the maximum valve opening of the tangential airway.The spiral airway valve opening is greater than or equal to 2/3 of the maximum valve lift.When the spiral valve opening is greater than1/2 of the maximum valve lift,the swirl ratio is fully improved.Screw cut 12/10,screw cut 12/9,screw cut 11/12 in terms of flow coefficient and swirl ratio:on the one hand,the flow coefficient and swirl ratio of screw cut 11/12 are the same as screw cut 12/12,On the other hand,one of the indicators of the flow coefficient and swirl ratio of the screw cut 12/10,screw cut 12/9 has been comprehensively improved,and the other index has reached the level of screw cut 12/12.A circular stratification study of EGR in the cylinder was carried out.The results show that the gas in the spiral air channel introduction mode,the pits and the combustion chamber distributed more CO₂ relative to the central area,and gradually formed a more regular annular distribution.The gas in the tangential air channel introduction mode has more CO₂ distribution on the side near the tangential air channel,and less CO₂ distribution around the center of the cylinder.Under different EGR rate conditions,by changing the EGR rate of the gas introduced into the single port,the amount of exhaust gas in the cylinder can be increased,thereby increasing the concentration of exhaust gas in the cylinder,which has a greater effect on EGR stratification.Under different EGR pressure conditions,by changing the EGR pressure of the gas introduced into the single air passage and increasing the amount of exhaust gas introduced into the single air passage,the concentration of the exhaust gas in the cylinder can be increased,which has a significant effect on the EGR stratification.Under different EGR temperature conditions,by changing the EGR temperature of the gas introduced into the single air channel,the in-cylinder EGR rate is reduced,but the effect is smaller and the effect on EGR stratification is smaller.The combustion and emission process of the circular stratification of EGR in the cylinder shows that:under homogeneous EGR conditions,compared with the final value of 12/12 screw cut under the same valve condition,10/12 screw cut and 9/12screw cut,The final value of NOx 12/8 increased by 2.3%,6.3%,and 4.5%respectively;the final value of Soot decreased by 7.6%,21.4%,and 13.7%;the final value of CO decreased by 3.7%and 12.0%,A reduction of 6.5%.Under the EGR stratification conditions,the final values of NOx of screw-cut 10/12,screw-cut 9/12,screw-cut 12/8 increased by 1.8%and increased compared to the final value of screw-cut 12/12 under the same valve condition 6.2%,an increase of 3.9%;Soot’s final value decreased by 7.0%,25%,and 14.8%;CO final value decreased by 3.8%,15.1%,and 8.5%,respectively,Compared with homogeneous EGR,the NOx increase in the in-cylinder EGR annular stratification is reduced,Soot and CO production are reduced.