Numerical Study on Chemiluminescence Characteristics in Ammonia-Hydrogen-Air Counterflow Diffusion Flames

This numerical study presents a kinetic analysis of chemiluminescence characteristics in NH3-H2-air counterflow diffusion flames, focusing on the effects of the NH3 blending ratio (XNH3, 0–40%) and strain rate (α, 60–180 s−1). A reaction mechanism containing OH*/NO*/NH*/NH2* radicals for NH3-H2 flames is validated. The results show that the temperature gradually decreases with increasing XNH3 and α. The mole fraction of OH* radical decreases with increasing XNH3 and vice versa with α, which is primarily governed by the formation reaction R254: H + O + M = OH* + M. R255: N2O + H = OH* + N2 is significantly enhanced by NH3 blending, leading to an additional OH* peak on the fuel side of NH3-blended flames. All nitrogen-containing radicals increase with XNH3, but only NO* radical shows an increase when α increases. R280: N2A + NO = N2 + NO* dominates the formation of NO* radical, with the key pathway being NH3 → NH2 → NH → N2A → NO*. NH2* radical has the highest mole fraction of all radicals and is formed through NH3 → (NH2 → NH) → NH2*, in which R302: NH* + H2 = NH2* + H is an important conversion reaction between NH* and NH2* radicals. This study facilitates further understanding and engineering applications of NH3-H2 combustion technology.