Simulation Research On Performance Improvement Of Marine EGR Diesel Engine

With the increasingly stringent emission regulations,EGR technology,as an effective measure to reduce NOx emissions within the diesel engine,has been widely studied.In the steady-state conditions,the diesel engine can achieve the best compromise between economy and emissions through the closed-loop feedback control of EGR rate.However,in the transient process,the linear correlation between intake oxygen content and NOx emission is larger(compared with EGR rate)and EGR rate is no longer the only feedback control variable in transient process.Although the oxygen content sensor can accurately measure the oxygen concentration of the intake air,it is difficult to measure the real-time oxygen concentration of the intake air due to the lag of the oxygen sensor and the big impact of working environment temprature.The introduction of the EGR system reduces the exhaust gas flow through the turbine and in turn reduces the power of the turbine,which causes the matching operation point of diesel engine and the compressor to move to the surge boundary.In addition,when the diesel engine operates at high load,the maxium of pressure of the diesel engine may exceed the limit and mechanical load may increase.In the early transient loading process of EGR diesel engine,due to the hysteresis effect of the turbocharger,the insufficient intake of diesel engine and the decrease of air-fuel ratio lead to serious emission of Soot.In order to solve the problems mentioned above,this paper uses GT-power software to establish the 6EX340 EF marine two-stroke low-speed diesel engine model,and verify the accuracy of the model through the test data.On the basic of the model,the following studies were conducted:(1)Correlative Analysis of Oxygen Content and NOx generation.(2)Reliability Verification of Artificial Neural Network in Prediction of Intake Oxygen Content.(3)Study on the Influence of Inlet and Exhaust Bypass and High Working Deflate on EGR Diesel Engine Performance.(4)Study on the Influence of Different Loading Modes on EGR Diesel Engine Performance.(5)Research on Improvement of Transient Loading Process of Marine EGR Diesel Engine with High Pressure Gas Source.(6)Optimize the Performance of the EGR Diesel Engine Based on Multi-objective Optimization Algorithm.Simulation results show that:Whether in transient conditions or in steady state conditions,the linear correlation between the intake oxygen content and the NOx emission is greater thanthe linear correlation between the EGR rate and the NOx emission.So,intake oxygen content can be used as feedback control variable to control EGR diesel engine.At the same time,the conventional oxygen sensor has been verified to have obvious hysteresis during the transient process,And the prediction of intake oxygen content of artificial neural network can well approximate the real-time simulation value of intake oxygen content.Through the study of intake and exhaust bypass and high operating conditions Deflation,we can draw conclutions that reasonable intake and exhaust bypass can improve the surge and reduce fuel consumption and high operating conditions deflation can make EGR diesel engine's burst pressure not exceed the limit in 110% condition and above-30 ?.In the abstract of loading strategy,increasing the loading time can improve the whole performance of EGR diesel engine well,at the same time air-fuel ratio optimization can effectively improve the phenomenon of serious Soot emission.In addition,this paper also puts forward the optimization strategy of transient loading process of EGR diesel engine based on high pressure air source.After optimization,air-fuel ratio can track the best air-fuel ratio well under steady-state conditions,meanwhile Soot emissions can reduce greatly in the case of increasing NOx emissions a little.Finally,the best EGR valve opening and intake and exhaust bypass valve opening can be found under different conditions through the multi-objective optimization and the feasibility of using artificial neural network to predict the oxygen content of intake air in the feedback control of intake oxygen content and the necessity of the high-pressure air source in the transient loading process are further verified by the "multi-objective optimization + multi-strategy" joint simulation.