Experimental and numerical analysis on influence of air staging in a tangential flow burner for pure ammonia combustion

Abstract

The combustion of pure ammonia has garnered significant attention due to the challenges involved in stabilizing flame. This study investigates pure ammonia flames using an innovative staged burner, with experiments conducted across three burner configurations: 2-stage, 3-stage, and 4-stage setups. In addition to the experimental work, comprehensive large eddy simulations (LES) are performed to assess the effects of thermal intensities, global equivalence ratios, and staging on pure ammonia flames. A wide flame stability range, with equivalence ratio spanning from 0.5 to 1.2, is achieved while maintaining minimal NO emissions and nearly zero ammonia slip. Key factors such as mixing, preheating temperatures, and local oxygen concentrations are found to play crucial roles in pure ammonia flame stabilization. For lower energy inputs, the 2-stage configuration exhibits optimal combustion performance with minimal NOx emissions (4.12 PPM/kW) and no ammonia slip. In contrast, the 4-stage configuration yields the lowest NOx emissions, reaching 0.8 PPM/kW. Furthermore, under comparable thermal intensities, variations in local oxygen concentrations significantly influenced NOx emissions, with the lowest NOx levels (143 PPM) observed in the 4-stage setup under stoichiometric conditions. At high thermal inputs with the 2-stage configuration, notable levels of N and NH species are identified at burner’s exit, contributing to reduced exit temperatures. Overall, the 4-stage configuration at high thermal inputs achieves the lowest NO flow rates (0.34 g/kW·hr), eliminates ammonia slip, and minimizes the N and NH radical species at the burner’s exit.