Turbulent burning velocity of NH3/H2/air mixtures spherical flames: Effects of differential diffusion and turbulent stretch

The combustion characteristics of ammonia/hydrogen/air mixtures flame under different equivalent ratios (0.6–1.0), and hydrogen ratio (0.3–0.5) in a wide range of turbulence intensity were investigated. The result shows both differential diffusion and flame chemistry affect the flame morphology and burning velocity of lean and stoichiometric mixtures. With the increase of hydrogen ratio, not only can chemical reaction be enhanced, but also heat and mass diffusion of the flame front can be promoted, thus accelerating flame propagation. In addition, the strong turbulent stretch of the turbulent field gradually plays a dominant role in the development of flame and causes the flame to wrinkle even more. Based on the turbulent flame Reynolds number (ReT,flame), the accelerated propagation processes are analyzed, and further, the influences of differential diffusion and turbulent stretching are taken into account by Le and Ka numbers. The general correlation of turbulent burning velocity (ST) is obtained, and the applicability of the correlation based on Da and Ka for ammonia/hydrogen/air mixtures turbulent combustion is verified. In addition, a unified scaling of turbulent burning velocity (ST) suitable for different equivalent ratios and hydrogen content conditions is obtained by rearranging with Le.