Study On The Combustion Process Within The Cylinder Of Port-Fuel-Injection Hydrogen Internal Combustion Engine Based On Les

In China,about 70% of the annual increased oil consumption is cost by the increasing vehicles,and the corresponding exhaust emissions have become the major source of air pollution sources in large cities;therefore,exploring novel technologies to save energy and reduce emissions has been significant to the further development of internal combustion engine industry.Hydrogen is widely regarded as an ideal clean alternative fuel due to its many advantages(such as concentrated energy density,diverse preparation methods,zero carbon emissions from combustion,renewable resource,and so on).However,the actual performances of port-fuel-injection hydrogen-fueled internal combustion engines(PFI-HICEs)are seriously weakened by some abnormal combustion phenomena,such as the back fire induced by the hydrogen accumulation within intake duct,the pre-ignition caused by the resisted hydrogen around the inlet valve and pipe,and so on.Therefore,it is necessary to explore the combustion process of hydrogen and the related mechanism within the cylinder of PFI-HICEs,study the effects of macro-control parameters(such as hydrogen injection timing,hydrogen injection flow,ignition timing,and so on)on combustion performance and the formation of NO within HICEs.In this paper,a certain PFI-HICE is used as prototype to study the effects of macrocontrol parameters(including hydrogen injection timing,hydrogen injection flow,and ignition timing)on the combustion performance and NO emission by the method of large eddy simulation(LES)upon the CONVERGE platform.First,the effects of hydrogen injection timing and hydrogen injection flow on the hydrogen-air mixing process and the quality of mixtures,the results show that,during the formation of the mixture,with the delay of injection timing and the increase of injection flow,the mass of hydrogen-air mixture within the cylinder first increases and then decreases.Proper hydrogen injection timing and hydrogen injection flow can ensure that the hydrogen accumulation in the intake port is the least(which means the lowest potential of backfire);meanwhile,the hydrogen-air mixture within the cylinder is most uniform,with a higher equivalent ratio near the spark plug and wider regions of strong turbulence(indicated by higher kinetic energy regions and higher intensity of vortices),all those are beneficial to ignition and flame propagation.Later,the effects of ignition timing together with hydrogen injection timing and hydrogen injection flow on the combustion process within the cylinder were numerically studied.The results show that,as the advance of ignition timing from top-dead-center(TDC),both the averaged pressure and the averaged temperature within the cylinder are gradually increased,the rapid combustion period first decreases and then increases,and the turbulent characters(including both the vortex within the cylinder and the tumble flow around Y axis)decrease after a period of initial rising.With the delay of injection timing,both the averaged pressure and the averaged temperature within the cylinder first increase and then decrease.The vortex within the cylinder and the value of the tumble flow around Y axis are related to the homogeneity of hydrogen-air mixture.The homogeneity of hydrogen-air mixture within the cylinder is the best,both the vortex and the tumble flow around Y axis within the cylinder are the highest.Last,the effects of hydrogen injection timing and ignition timing on the production of NOx within the cylinder of PFI-HICE are numerically studied.The results show that,both the spatial and the temporal distribution of NO element within the cylinder are similar to those of OH element;however,the generation rate of NO element lags behind OH element.During the combustion of hydrogen and air within PFI-HICE,as the advance of ignition timing from TDC and/or the delay of hydrogen injection timing,the production amount of NO is raised,the growth is monotonous to ignition timing but non-monotonic to the injection timing.Furthermore,the more homogeneity of hydrogen-air mixture an injection timing could realize,the larger amount of NO is produced.