| Abstract:Hydrogen and ammonia have received widespread attention as clean and renewable fuel. Laminar flame speed is a crucial characterization parameter in fuel combustion progress. H2O as a combustion product of hydrogen ammonia mixed fuel affects their combustion characteristics. This paper investigates the mechanism of the influence of water vapor dilution (0~50%) on the combustion characteristics of NH3/H2 under the conditions of initial pressure of 101.3kPa, chemical equivalence ratio of 0.8~1.4 and hydrogen blending ratio of 0.3~0.7, by the method of a constant volume combustion bomb experiment with one-dimensional laminar premixed flame numerical calculation. The results show that the laminar speed of NH3/H2 first increases and then decreases with the increase of equivalence ratio, with a peak appearing around 1.2 equivalence ratio. As the dilution ratio of water vapor increases, the peak shifts towards equivalence ratio of 1.1, and the sensitivity affected by the equivalence ratio decreases. Chemical kinetic analysis shows that dilution effect has the greatest impact among different physical and chemical effects of water vapor. Branch chain reactions such as R1, R3, and R68 in the main elementary reactions promote laminar flame propagation, while branch chain reactions such as R16, R58, and R60 have inhibitory effects. The increase of water dilution ratio will increase the sensitivity coefficient of key branch chain reactions to laminar combustion speed, and the growth trend of sensitivity coefficient will continue to increase. With increase of the water dilution ratio, the molar fractions of free radicals such as NO, N2O, OH in the reaction zone significantly decrease, resulting in the decrease of the NH3/H2 laminar flame speed. |