Simulation And Experimental Research On Raising Exhaust Temperature Of Diesel Engine Under Low Speed And Small Load

With the increasingly stringent emission regulations around the world,China has gradually implemented more stringent emission regulations,especially with the release of the National VI emission regulations,the emission limits for diesel engines have been further reduced,and the nitrogen oxide(NOx)emissions of diesel engines The requirements have become more stringent.Under urban road conditions,due to traffic congestion,urban road complexity,and the presence of traffic lights,diesel engines are often in low-speed and light-load conditions,making diesel engine exhaust temperatures very low,and diesel engines are selectively catalyzed when the exhaust gas temperature is too low,the Selective Catalytic Reduction post-treatment system will make the urea solution unable to be fully pyrolyzed and hydrolyzed,and crystallization will also occur,which will result in the urea solution being unable to be fully converted into ammonia(NH3).In the state,the adsorption efficiency of NH3 on the catalyst is also very low,and the activity of the catalyst is also affected by the exhaust temperature.Therefore,the conversion efficiency of NOx is low or the after-treatment system cannot work.Under urban road conditions,in order to ensure the SCR after-treatment The system works normally,so the diesel engine exhaust heat management strategy is very necessary.In this paper,the original engine model CA4D28C5 was established through GT-Power software,and the original engine model was improved.The simulation models of the intake throttling strategy,the non-cold EGR strategy,the post injection strategy,and the intake throttling strategy were established respectively.The coupling model with the other two strategies,and the transient model coupled with three strategies are established at the same time.The original machine simulation model is verified by the original machine test data.After analyzing the working conditions,1200r/min and 20% load are selected,and the simulation is carried out.The calculation of the model shows the impact of three exhaust temperature thermal management strategies and their coupling strategies on diesel engines.The intake throttling strategy can greatly increase the exhaust temperature,and the maximum increase is about 100℃.Exhaust temperature is gradually increasing as the degree of flow increases,but the fuel consumption and NOx emissions of diesel engines are also increasing sharply.Throttling strategies have a great influence on the combustion of diesel engines.Under the premise of meeting the exhaust temperature,the throttle should be reduced as much as possible.The increase of exhaust temperature by non-cold EGR strategy is relatively small,and the increase is about 20～30℃,but it has a small impact on the NOx emission and fuel consumption of diesel engines.The post-injection strategy has a relatively small increase in exhaust temperature.It is also relatively small,with an increase in the range of 20～30℃.The far rear injection angle and the rear injection volume can reduce NOx emissions within a certain range.The fuel consumption is slightly higher than the original engine.The air intake throttling strategy is coupled with other strategies.The exhaust temperature of the diesel engine can be further increased at the time,the fuel consumption is improved compared with the intake throttle strategy,and the NOx emission will be reduced when the after injection strategy is coupled.In transient operating conditions,using the coupling of three exhaust temperature thermal management strategies,the diesel engine exhaust temperature response will lag,and NOx emissions and fuel consumption are also improved compared to steady-state operating conditions,because the response of exhaust temperature is steady-state Phenomenon,here does not do too much research on transient conditions.A test bench was built to further verify the accuracy of the three exhaust heat management strategies and the simulation model of the coupling strategy through experiments,and to test and analyze the influence of rail pressure and main injection timing on diesel engine exhaust temperature.The best coupling strategy and specific plan for exhaust temperature thermal management are obtained.Rail pressure and main injection timing have a small increase in diesel engine exhaust temperature and have a greater impact on diesel engine combustion and emissions.Therefore,these two types of exhaust temperature The thermal management strategy is not adopted.According to the research and analysis of the test results,at 1200r/min and 20% load,the best strategy to increase the exhaust temperature of the diesel engine is the intake throttling coupled with the non-cold EGR and post injection strategy.Select 70kg/h for air volume,select 7.2℃A aTDC for rear injection strategy,near-rear injection angle of 12% of total circulating fuel injection volume,select 30℃A aTDC for far-rear injection angle,select total injection volume for far-rear injection 12% of circulating fuel injection.