Experimental study on the combustion characteristics of hydrogen/ammonia blends in oxygen

Abstract

Carbon-free ammonia and hydrogen have various disadvantages when used individually, which limits their application as clean energies. These disadvantages can be effectively overcome by combining them as ammonia/hydrogen mixtures in a rational manner. In this paper, the combustion of ammonia/hydrogen in oxygen (the basic form of combustion) is experimentally investigated at various experimental conditions. The results display that the laminar burning velocities of ammonia/hydrogen/oxygen mixtures increase with increasing fuel ratios. At P0 = 0.5 atm and φ = 1.0, the laminar burning velocity proliferated from 1.91 m/s to 4.7 m/s with the increase of fuel ratio from 0.5 to 2.0. As the equivalence ratio increases, the laminar burning velocity rises first and then decreases, with the highest point appearing at φ = 0.8. The initial pressure has minimal impact on the laminar burning velocity. At x = 0.5 and φ = 1.0, the laminar burning velocity decreased slightly from 3.16 m/s to 2.96 m/s with the initial pressure increased from 0.1 atm to 1.0 atm. The empirical correlation among the laminar burning velocity versus the equivalence ratio and hydrogen ratio is given, and the laminar burning velocity of ammonia/hydrogen/oxygen under varying hydrogen ratios (0 %–100 %) and equivalence ratios (0.5–1.5) at atmospheric pressure can be well predicted by the empirical equations. NO is the most emitted NOx substance from hydrogen/ammonia combustion. The amount of NO produced decreases gradually with the growing equivalence ratio. The results of this research can be utilized to renew the basic flame data of ammonia/hydrogen mixture and are important for the development and application of ammonia/hydrogen mixtures.

Keywords

• Carbon-free
• Ammonia/hydrogen/oxygen
• Fuel ratio
• Laminar burning velocity
• Empirical correlation