Effects Of Intake Pressure And EGR On Comprehensive Performance Of Gydrogen-blended Internal Combustion Engine

The wide application of internal combustion engines has caused rapid consumption of fossil fuels and pollution of the atmospheric environment.Hydrogen is considered to be the most suitable internal combustion engine fuel for low-carbon emission concept because of its zero carbon emission,sustainable regeneration and high calorific value.However,due to the physical and chemical properties of hydrogen and the limitations of hydrogen storage technology,it is difficult for mobile sources to store large amounts of hydrogen,which limits the development and application of hydrogen-fueled internal combustion engines.Therefore,the hydrogen-blended gasoline internal combustion engine makes a smooth transition from fossil fuels to low-emission clean fuels.In a hydrogen-doped internal combustion engine with hydrogen injection in the intake tract and direct in-cylinder gasoline injection,intake blockage may occur in the intake tract because of the high diffusivity of hydrogen gas.Although increasing the intake pressure can significantly improve the intake blockage,it will also increase the NO_x emission.To solve the problems of intake blockage and high NO_x emission in hydrogen-doped internal combustion engines with hydrogen injection in the intake tract and direct in-cylinder gasoline injection,the effects of intake pressure on the gas flow state in the intake tract,the homogeneity of hydrogen-air mixture,and the combustion characteristics and performance of hydrogen-doped internal combustion engines were analyzed.Under the synergistic effect of intake pressure and EGR rate,the influence weights of intake pressure and EGR rate on the comprehensive performance of hydrogen-doped internal combustion engine are determined by orthogonal test design;based on the multiplicative normalized combined weighting method,combined with the order relation analysis method(G1)and CRITIC weighting method,the evaluation index weights of comprehensive performance of hydrogen-doped internal combustion engine are established to study the influence of intake pressure and EGR rate on the comprehensive performance of hydrogen-doped internal combustion engine.The influence of the intake pressure and EGR rate on the overall performance of hydrogen-doped internal combustion engines was studied.The parameters of intake pressure and EGR rate were obtained by nonlinear regression analysis to optimize the performance of the hydrogen-doped internal combustion engine under full working conditions.The results of the study showed that:increasing the intake pressure improved the degree of intake blockage at low speed(1000r/min),and also improved the homogeneity of the in-cylinder hydrogen-air mixture at low load conditions,increased the maximum in-cylinder pressure and temperature,and contributed to the increase of the indicated power and the indicated thermal efficiency of the hydrogen-doped internal combustion engine at low load conditions;however,the indicated thermal efficiency decreased with the increase of the load at high load conditions.The increase in intake pressure increases NO_x emissions while decreasing CO emissions and HC emissions.After the introduction of EGR rate,the effects of load,intake pressure and EGR rate on the overall performance of hydrogen-doped internal combustion engines at 1000 r/min,3000 r/min,4500 r/min and 6000 r/min were as follows:load>EGR rate>intake pressure,EGR rate>load>intake pressure,EGR rate>load>intake pressure and EGR rate>load>intake pressure.The values of load,intake pressure and EGR rate parameters were obtained to optimize the overall performance of the hydrogen-doped internal combustion engine at 1000r/min,3000r/min,4500r/min and 6000r/min speeds.The values are0%-0.18MPa-5%(load-intake pressure-EGR rate),100%-0.18MPa-0%,70%-0.12MPa-5%and 70%-0.12MPa-5%,respectively.The values of intake pressure and EGR rate that make the overall evaluation of the hydrogen-doped internal combustion engine optimal are obtained by nonlinear regression analysis at full operating conditions.For example,at 1000r/min and 10%load condition,the intake pressure of 0.1819MPa and EGR rate of 8.76%gave the highest overall performance rating of the hydrogen-doped internal combustion engine,and the overall performance of the hydrogen-doped internal combustion engine was optimal at this time.