Research On The Impact Of EGR On Thermo-mechanicai Stress Of The Stoichiometric Natural Gas Engine

In recent years, faced with the serious environmental problems, the automotiveindustries have been introduced new regulations to control pollutants of automobile exhaustemissions. With the introduction of the Euro Ⅵ emission regulations, stringent emissionrequirements makes natural gas engines to add three-way catalytic to reduce NOx emissions,in order to ensure the three-way catalytic conversion efficiency, natural gas enginecombustion mode from the traditional lean-burn combustion mode into thestoichiometric.combustion mode. The engine combustion speed and combustiontemperature is higher, the in-cylinder heat load increase when the concentrations of mixtureis high. In order to solve the high thermo-mechanical stress problem of natural gas engines,EGR was added to the combustion mode to seek a solution in this paper.EGR technology for the study of the influence of the thermo-mechanical stress whencompared with natural gas engines from the micro aspect, we use AVL-FIRE software toestablish the stoichiometric natural gas engines simulation platform and to study theinfluence of different ignition timing and EGR rate of engine performance and to researchthe flame propagation, the concentration field, influence of temperature field in cylinder.Conclusions are as follows:The stoichiometric natural gas engine heat release rate curve is steep, the peak of heatrelease rate is larger, make the in-cylinder temperature, thermal loads and pressurehigher.When the initial nuclearis formed near the spark plug, then the ball of flame spread in thecombustion chamber. With the combustion of naturalgas, the spatial distribution isconsistent with the flame surface density distribution. With the affection of mixturecombustion, cylinder temperature field distribution and concentration field are basically thesame.With the increase of EGR rate, combustion starting point go backward, maincombustion-term grow, burn rates decrease, heat release rate drop, the temperature decrease;but the in-cylinder pressure decrease, and the maximum pressure crank angle wantbackward, making the engine power dropped significantly.With the advance of ignition timing, the combustion starting point go forward, themain combustion period is shortened, the burning speed, heat release and cylinder pressure increase. The maximum cylinder pressure and temperature crank angle go forward. So wecan adjust the ignition timingto resolved engine power decline caused by higher EGR rate.Changing the EGR rate and the ignition timing make the same maximum cylinderpressure crank angle.when ignition timing is-32°CA and EGR rate is30%, the maximumcylinder temperature drops about600K,and the cylinder temperature distribution isconsistent with the of the different EGR rate.