Experimental and kinetic study on laminar burning velocities of NH3/CH4/H2S/air flames

Abstract

Recently, ammonia has been favored by scientists and engineers as a new type of carbon-free fuel for future carbon–neutral society. Before large-scale application, some existing drawbacks including extremely low reactivity need to be overcomed by enhancing combustion technology. Blending ammonia with sour gas, a type of natural gas resource containing amounts of H2S, can be a solution to enhance the combustion of ammonia as well as efficiently utilize natural gas resource. In this study, the laminar burning velocities of NH3/CH4/H2S/air flames were investigated using the Heat Flux method over a wide range of equivalence ratios and and mixing ratios. A kinetic model for NH3/CH4/H2S/air flames simulation was developed by integrating ammonia sub-mechanism with the mechanism of Han et al. and validated based on the experimental data. The experimental results show that the H2S addition has a negative effect on the flame speed, which reaches 13.36 % decrease at ϕ = 1.25 when the H2S mole fraction is 12 %. Kinetic analysis was performed for exploring the effect of H2S addition on the laminar flame propagation of NH3/CH4/H2S mixtures. The results show that the elevated H2S content significantly impacts the radicals pool in flame, where the mole fraction of H, OH radicals decreases while the S-containing species content increases obviously. Sensitivity analysis shows that the reactions involving S-containing species become important for laminar flame speed determination at high H2S content. Besides, the increament of NH3 ratio in the fuel significantly improves the concentration level of NH2 radical in the flame, leading to the increased importance of NH2 chemistry.