Effects Of Spaced Injection Mode On The Combustion And Performance Of The HICE

As the fossil energy is being exhausted and the atmospheric pollution is exacerbating,a growing number of researchers are beginning to explore an alternative pathway which is more efficient,clean and renewable energy.Hydrogen has drawn wide attention from many researchers with its advantages of high diffusivity,wide flammability limit,low ignition energy and clean combustion.And it is recognized as the most promising alternative fuels for vehicles in 21st-century.For the hydrogen internal combustion engine(HICE)system with port fuel injection,due to the small density of hydrogen,the hydrogen injecting into the intake port from the injection system will expand to different degrees,which will block the entry of air because of the limitation of intake port.But the injection mode has a significant effect on the air flow in the intake port.Two types of injection modes,such as the dual injection with symmetric arrangement and with spaced arrangement along the axis of intake port,were proposed to improve the blockage of intake port and formation of the hydrogen-air mixture.And the effects of three types of injection modes and the nozzle diameter on the mixture formation,combustion performance,the backfire and pre-ignition problems under different equivalent ratios and engine speeds were investigated by using 3D numerical simulation method based on AVL-Fire.It is found that compared with using single pipe injection,using dual injection not only improves the power and economic performance,but also reduces the residual hydrogen mass in intake port,which alleviates the problem of intake port blockage to some extent,and is beneficial to restrain the backfire.For the dual injection,the spaced dual injection improves the mass flow in intake port and alleviates the problem of intake port blockage better.And the uniformity of hydrogen-air mixture is improved,which makes the element H and O unite with OH more quickly,and the reaction is more violent.Therefore,the combustion velocity is improved,which is beneficial to increase in-cylinder pressure,indicated power and indicated thermal efficiency,especially when the equivalent ratio is 0.67.However the NOx emission increases.The uniformity coefficient of mixture is gradually decreasing and the indicated power and indicated thermal efficiency are increasing first and then decreasing with the increase of nozzle diameter,and there is a peak when the nozzle diameter is equal to 4mm.The temperature in cylinder is not only higher by using the spaced dual injection,but the distribution of high temperature area also expands.Thus the pre-ignition is more likely to occur.But the residual hydrogen mass in intake port reduces obviously after closing the intake valve,so backfire can be restrained.The residual hydrogen mass is gradually decreasing with the increase of nozzle diameter,so backfire also can be restrained.