| The study is based on a natural gas engine with thermochemical fuel reforming mode,which is analyzed by means of experiments and calculations.It systematically researched the influence of engine operating boundary conditions on the thermochemical fuel reforming mode.First,it analyzed the formation and distribution characteristics of H2in the reforming cylinder,and summarized the chemical reaction paths of H2generation on the flame surface.Then,the influence of boundary conditions were investigated,such as intake air uniformity,intake air temperature and exhaust gas recirculation（EGR）.The mechanism of the influence of combustion status in the cylinder on hydrogen production is revealed.This study used CONVERGE software to simulate the combustion of reforming cylinder.It is found that the generation process of H2 in the cylinder can be divided into two stages:rapid generation period and slow generation period.It was further found that flame propagation is the direct factor that caused the rapid generation of H2.As the combustion proceeded,the oxidation products in the burned area would further react slowly to accumulate H2.The distribution of H2 in the cylinder generally showed the characteristics of"more H2 in low-temperature regions and less H2 in high-temperature regions".Next,the study continued to carry out the kinetic analysis to calculate and analyze the three chemical reaction paths that generate H2,and found that H is a very important intermediate particle in the H2 generation process.The influence of intake air uniformity and temperature were analyzed.The study found that intake mixer can help to accelerate the mixing rate of air and reformed gas,and improve the uniformity of air intake.Thereby reducing the cycle fluctuation rate of the whole engine and improving the fuel reforming efficiency.On the other hand,increasing the intake air temperature can increase the initial boundary temperature of fuel modification,improve the combustion of the reforming cylinder,enhance stability,and reduce the overall emissions and fuel consumption rate.However,under low load conditions,it would also cause the decrease of H2 and CO.Subsequently,the influence of EGR on fuel reforming in the cylinder was analyzed.The study found that the combustion condition in the modified cylinder is better without EGR compared to 25%EGR.Compared with methanol and isooctane enrichment,the fuel reforming ability of natural gas enrichment is stronger without EGR.The calculation found that the increase of EGR rate caused the deterioration of combustion,including that average temperature decreased.That is,the reformed gas EGR showed a negative effect on the overall reforming cylinder combustion,which was not conducive to fuel reforming,and caused a decrease of H2 production. |
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