Research On Influencing Factors Of Diesel Engine SCR Performance In Plateau Environment

Diesel engines are favored by people because of their excellent power and economy,occupying more and more market share,with the development of industry and economy,the number of cars has increased year by year,and environmental problems caused by engine exhaust pollutants as the source Increasingly severe and stricter emission regulations.The proposal of National Six has brought new challenges to exhaust gas aftertreatment technology.The main contradiction of diesel engine emission control is to reduce NOx and PM emissions.Selective Catalytic Reduction(SCR)is The method specifically used to reduce NOx emissions from diesel engines has mature technology and high efficiency,and has been widely used.NOx conversion efficiency and NH3 escape amount are the two most important SCR performance evaluation indicators,and also the key to meeting the national six regulations.Changes in exhaust temperature and exhaust flow will have an important impact on both,while diesel engines operate at different altitudes When the exhaust temperature and exhaust flow are different,this requires the SCR control strategy to have better altitude adaptation and regulation capabilities.Studying the influencing factors and rules of SCR performance at different altitudes can enrich the theoretical basis for the optimization of SCR control strategy,and is of great significance for improving the adaptability of SCR altitude.Taking a 2.0L high-pressure common rail diesel engine as the research object,relying on the AVL test bench and exhaust gas collection equipment,combined with the atmospheric simulation system,the diesel engine external characteristics tests were conducted at 80 kPa,90 kPa,and 100 kPa atmospheric pressures respectively to study the diesel engine at different altitudes Performance,install an SCR system matching the engine,explore the impact of exhaust temperature,exhaust flow and altitude changes on NOx conversion efficiency and ammonia slip,use the test data to build a one-dimensional model using AVL BOOST,with different altitudes as Based on the analysis of the influence of exhaust temperature and exhaust flow analysis on the performance of SCR,the response surface method is used to design the plan and a prediction model is proposed,and finally the response surface analysis is performed.The research results are as follows:(1)The power and economy of the diesel engine will decrease as the altitude increases.The higher the altitude,the lower the torque and power of the diesel engine,and the higher the fuel consumption rate.The difference in diesel engine performance at different altitudes at low speed is more obvious;The exhaust temperature will increase and the exhaust flow will decrease;NOx and O2 emissions from diesel engines will decrease with altitude,and CO,CO2,and HC emissions will increase with altitude.(2)NOx conversion efficiency increases first and then decreases with increasing temperature.The conversion efficiency in the three temperature range from 230? to 320? increases from 43.3%to 78.6%,an increase of 35.3%.After 320?,the conversion efficiency increases with temperature the high increase decreases,and the conversion efficiency reaches a maximum of 86.7%at 380?,then the temperature continues to rise but the conversion efficiency gradually decreases.At 560?,the conversion efficiency drops to 59.5%,which is 27.2%lower than the maximum conversion efficiency;ammonia escape as the temperature rises,the amount decreases first and then rises slightly.From 230? to 410 ?,the amount of ammonia slipped from 348.3ppm to 20.6ppm,a total decrease of 327.7ppm,a drop of 94%.After that,the temperature continued to increase with a slight increase,the ammonia slip increased from 20.6 ppm to 73.5 ppm,a total increase of 52.9 ppm.The NOx conversion efficiency generally decreases with increasing exhaust gas flow.As the temperature rises,the exhaust gas flow has a smaller and smaller effect on NOx conversion efficiency.The maximum conversion efficiency at 250 ? is 49.7%and the minimum conversion efficiency is 28.2%,A decrease of 21.5%,a conversion efficiency of 300? decreased by 14.6%,and a conversion efficiency of 350?decreased by 8.7%;with the increase of exhaust flow,ammonia leakage increased continuously,and the lower the temperature,the ammonia leakage changed with the exhaust flow The greater the magnitude.(3)The higher the altitude,the higher the NOx conversion efficiency.As the speed increases,the conversion efficiency decreases.At low speed,the effect of altitude is significant,and at medium and high speeds,the effect is less;the higher the altitude,the lower the amount of ammonia escape,and the speed from low to high The ammonia escape amount decreases first and then increases.At low speeds,the ammonia escape amount has a small altitude difference,and at high and medium speeds,the difference is larger.The maximum difference between ammonia escape amounts at different altitudes occurs at 2400 r/min.The 80 kPa escape amount is 17.8 ppm and the 100 kPa escape amount is 138.8ppm,a difference of 121ppm,the smallest difference is 13.4ppm at 1400r/min.(4)Combine the experimental data and SCR parameters,use AVL BOOST to establish a one-dimensional model.The simulation results show that the NOx conversion efficiency changes with temperature at three altitudes.The exhaust temperature rises and the conversion efficiency rises first and then decreases.The higher the altitude The lower the NOx conversion efficiency;as the temperature increases,the ammonia slip decreases first and then increases,and the higher the altitude,the less ammonia slip.At three altitudes,NOx conversion efficiency decreases with the increase of exhaust flow rate,but the reduction rate is different at different temperatures.Exhaust flow rate at low and high temperatures has a greater impact on conversion efficiency.At the same temperature,altitude the higher the NOx conversion efficiency decreases with the exhaust flow rate;the greater the exhaust flow rate at different altitudes,the NH3 escape amount increases continuously.The higher the altitude,the greater the ammonia escape amount,the same exhaust temperature and exhaust Under the air flow,the amount of ammonia escaping from the plain is more than that from the plateau.(5)Using response surface methodology for experimental design,analyze the effects of atmospheric pressure,exhaust temperature and exhaust flow interaction on NOx conversion efficiency,NH3 leakage and exhaust O2 content,and establish a prediction model,the results show that:exhaust Temperature is a significant factor that affects NOx conversion efficiency.The interaction of exhaust gas temperature,exhaust flow rate and atmospheric pressure have a great influence on NOx conversion efficiency;exhaust temperature and exhaust flow rate are significant factors for NH3 leakage.The interaction has the greatest impact on NH3.The lower the exhaust temperature,the greater the exhaust flow,and the greater the ammonia leakage.Exhaust flow and atmospheric pressure are significant factors affecting exhaust oxygen content.The interaction between the two affects O2 content.The maximum,the higher the altitude,the greater the exhaust flow,the higher the exhaust oxygen content.