Numerical study of the effect of pressure on the combustion characteristics of ammonia/coal-derived syngas mixture under gas turbine operating conditions

Abstract

This study investigates the influence of pressure variation on combustion properties, including laminar burning velocity and ignition delay time, as well as emissions in gas turbine conditions. Based on numerical simulations and using Matlab, the impact of pressure on the relationship between laminar burning velocity and free radicals, as well as the relationship between ignition delay time and laminar burning velocity, were analyzed. The results of Matlab curve fitting suggest that the decrease in free radical concentration due to increased pressure is the main cause of the reduction in laminar burning velocity. The presence of reactions such as H + O2 = O + OH and all ammonia-related reactions results in a linear relationship between the laminar combustion velocity and max(H) or max(NH2 + H), which varies with pressure in mixed ammonia combustion. Moreover, the linear correlation coefficient between the laminar combustion velocity and free radicals is a function of pressure. Using a one-dimensional laminar premixed model and a zero-dimensional closed reactor model, this study has identified a power function relationship between the laminar combustion velocity and ignition delay time in synthetic gas mixed with ammonia combustion, where the coefficients and exponents of the power function are functions of pressure. Moreover, these two fitting relationships are independent of equivalence ratio and fuel ratio. Finally, the analysis of NO emissions indicates that the NO produced by chemical pathways affects the chemical equilibrium of NO produced by thermal pathways. Additionally, the reaction CO + OH = CO2 + H initially produces some NO in the thermal pathway·NH3 participates in reactions after H2 and CO have reacted. Lastly, it was found that the increase in pressure promotes the reaction NH + NO = N2O + H, which leads to a decrease in the molar fraction of NO with increasing pressure.