Mechanism Of Action Of Pre-ignition On Backfire In Hydrogen Internal Combustion Engine

Automobile industry is facing enormous challenges under the dual pressure of energy conservation and environmental protection,and it is imperative to find new clean energy.Hydrogen energy is expected to become the excellent alternative to replace conventional fossil fuels for vehicle engines and has been attracted widely attention because of its clean,renewable characteristics and good combustion performance for automobile engines.As the normal ignition energy of hydrogen is very low,it is not easy to cause misfire when used as an alternative fuel for internal combustion engines,but it is easy to cause abnormal combustion such as pre-ignition and backfire.Pre-ignition and backfire not only cause the engine performance to drop sharply,but cause the engine to fail to operate normally and even flameout.Therefore,it is necessary to investigate the mechanism,characteristics and influence factors of pre-ignition and backfire of hydrogen internal combustion engines,and explore mechanism of action of pre-ignition on backfire,so as to provide a theoretical basis for inhibiting or eliminating the abnormal combustion of hydrogen-fueled engine,so as to promote the practical process of hydrogen internal combustion engines.Based on the three parameters of fuel-air equivalence ratio,residual gas fraction and reactant temperature,this paper investigates and quantifies the pre-ignition and backfire through the pressure parameters,temperature parameters and distribution of mixture concentration,proposes and defines the pre-ignition intensity I_P and backfire intensity I_B,analyzes the significance of influence of each parameter on pre-ignition and backfire,then combines residual hydrogen mass in the inlet,pre-ignition intensity I_P and backfire intensity I_B to deeply explore the mechanism of action of pre-ignition on backfire.The results show that whenΦis greater than or equal to 0.8,backfire occurs in the hydrogen internal combustion engine,which indicates that pre-ignition will not lead to backfire when the concentration of hydrogen-air mixture is low,but pre-ignition will lead to backfire when the concentration of hydrogen-air mixture is high.The I_P is raised,the residual hydrogen mass in the inlet is increased,and the I_B is raised with the increase ofΦ.The I_P is dropped,the residual hydrogen mass in the inlet is raised,and the I_B is decreased with the increase of residual gas fraction.The I_P is raised,the residual hydrogen mass in the inlet is increased,and the I_B is raised with the increase of T₅₀₀.The I_P is 1.0,and the I_B is 1.0 whenΦ=1.0,RGF=0.06,T₅₀₀=580K.This means that the largerΦis,the smaller residual gas fraction is,the higher reactant temperature is,the more serious pre-ignition is,the higher residual hydrogen mass in the inlet is,and then the more serious backfire is when is a high-temperature hot spot in the cylinder.Further analysis shows that when pre-ignition occurs in the hydrogen internal combustion engine,the higher cylinder pressure and temperature are,the greater rate of pressure rise and rate of temperature rise are,the greater loss of available energy is,the greater I_P is,the more serious pre-ignition is.The more serious pre-ignition is,the higher residual hydrogen mass in the inlet is,which indicates that There is a certain degree of vacuum in the inlet,and part of the hydrogen will inevitably remain in the inlet.Pre-ignition causes the pressure of the in-cylinder to rise sharply,and the unburned hydrogen-air mixture is squeezed into the inlet under the action of the high pressure of in-cylinder.When the flame front is not reached,the in-cylinder pressure continues to rise,and hydrogen fuel is further squeezed into the inlet.The faster flame front propagates to the inlet（The inlet has not been closed）when I_P is higher.The higher flame intensity is,the more intense combustion heat release of hydrogen fuel in the inlet is,and the higher pressure and temperature in the inlet are,which leads to the greater I_B,that is,the more serious backfire.This reveals that the more serious pre-ignition will lead to backfire,and there is a positive correlation between pre-ignition and backfire.