Study On Combustion And Emission Characteristics Of Hydrogen-air Mixture

Hydrogen energy,which is clean,renewable and has multi sources,it is treated as ideal substitute fuel for internal combustion engine.Hydrogen engine will generate NO_x which impede its development.This paper through simulation and experiment method studied chemistry mechanism and combustion and emission characteristics of hydrogen-air mixture in constant volume combustion bomb.The chemical reaction process of hydrogen-air mixture was studied by CHEMKIN software.The detailed mechanism of GRI-3.0 was simplified by means of sensitivity analysis,oxidation path analysis and temperature sensitivity analysis,and finally the HON simplified mechanism including the 24-step elementary reaction and the 16-mer element was obtained.The maximum error of the laminar combustion velocity calculated by the simplified mechanism is 7.2%,and the numerical calculation speed is 7 times higher than detailed reaction mechanism.Based on the CONVERGE software,the three-dimensional simulation model of the constant-volume combustion bomb was established,and the simplified reaction mechanism was taken as the combustion mechanism.The experimental results show that the maximum error of flame propagation velocity is 7%under different equivalent ratio,which can be used in combustion simulation of constant volume combustion bomb.Based on the model,the combustion process of hydrogen-air mixture under different working conditions was simulated.It was found that the distribution law of NO concentration and temperature in the radial direction of flame cross section is similar,which is the highest in the flame center and gradually decreases towards unburned area.In the area where temperature below1800K,the concentration range of NO is large,and the distribution of NO concentration in region where temperature is higher than 2000K is very uniform.The concentration has a great influence on the highest temperature in the burned area,the initial temperature just has a great effect on temperature in early combustion and has a little effect on the latter combustion.When?=0.5,the dilution ratio of N₂ increases from 0 to 20%,OH and NO decrease by 73%and 68%respectively,when the N₂ dilution rate is 30%,the flame appears extinguished.The data of OH distribution under different working conditions were obtained by OH-PLIF test methods.The results of the data analysis showed that the change of the gray value representing OH concentration with time was very similar with the calculated OH concentration distribution at?=0.5.With the development of combustion,the OH concentration in the flame center decreases gradually,and the OH concentration in the flame front is the highest,and there is a low OH ring in the pre-combustion area of the front surface.With the increase of the equivalent ratio,the flame front dimension decreases and the combustion stability increases,and the flame thickness decreases.The change of initial temperature has little influence on combustion stability and flame thickness.The concentration has a greater inpact on the flame stability and thickness.The dilution of N₂and N₂+H₂O will inhibit the combustion.With the increase of the dilution rate,the combustion and propagation rate of the flame will be reduced and the generation of OH will be significantly reduced.When N₂ and N₂+H₂O dilution rate is 20%,The sum of the gray values of the right half of the flame decreased by 46.5%and 76.5%,respectively,indicating that N₂+H₂O dilution had a stronger inhibition on combustion than N₂ alone.