Performance Analysis And Ignition Timing Optimization Of Hydrogen Engine At Medium And High Speeds With EGR

With continued attention to the global energy crisis and environmental issues,countries have begun to study and develop regulations to limit energy consumption and exhaust emissions from vehicles.The introduction of substitute fuels is in line with the current development trend of "energy saving and emission reduction" in the vehicle industry.Hydrogen is a kind of renewable clean energy without carbon base,compared with traditional internal combustion engines,hydrogen internal combustion engines have only NOx emissions.In addition,the unique physical and chemical properties such as high energy density,wide ignition limit,low ignition energy and fast combustion speed of hydrogen enhance the thermal efficiency and operational stability of the engine.However,the high combustion efficiency lead to too high pressure and temperature in the cylinder and increase the NO emission;at the same time,it will promote the occurrence of abnormal combustion,such as knock and pre-ignition.Frequent abnormal combustion under medium and high load and solving the contradiction between higher power output and NO emission are the main bottlenecks restricting the development of hydrogen engine.Based on this,the Exhaust Gas Recirculation(EGR)technology is used to regulate the combustion state in the cylinder of hydrogen engine and to explore the influence of EGR on the intake charge,combustion and emission of hydrogen engine.This paper first based on Jialing JH600 hydrogen-gasoline dual mode engine establishing simulation model,and based on AVL-Fire software,the model is verified.Then the main content is divided into two parts according to the research problem.The first part studies and analyzes the changes of filling composition,gas mixing state,combustion exothermic process and NO emission by adjusting different EGR rates.The second part takes 4500 r/min speed as an example to further analyze the overall performance of hydrogen engine by optimizing ignition timing,so as to optimize the optimal EGR rate and ignition timing.The results show that there is "air intake lag" phenomenon at low speed,and the in-cylinder charge increases with the increase of engine speed;the chemical dilution factor and heat effect increase obviously after the partial air EGR is replaced,and the chemical dilution factor is basically consistent with the EGR rate;The combustion temperature and pressure in the cylinder gradually decrease with the increase of the EGR rate;the effect of EGR on reducing the emission is remarkable,and the emission can even be close to zero at the high EGR rates.The maximum pressure and temperature in the cylinder increase with the advance of ignition timing,and the influence trend of ignition timing on heat release rate and indicated power is basically consistent;further analysis shows that the EGR rate have the most significant effect on the equivalent ratio in the cylinder,and the flame propagation speed is also strongly depends on the equivalent ratio during the combustion of hydrogen fuel.This article improves the incylinder combustion state by adjusting the ignition timing and improves performance of hydrogen engines at different loads and EGR rates.Finally,the optimum EGR rate and ignition timing are obtained by binomial fitting analysis and target range optimization.