Numerical evaluation of operating conditions in an array micromix combustor: Effects of hydrogen enrichment and inlet bulk velocity on flame stability

Abstract

The advancement of array micromix combustion technology supports hydrogen (H₂)-enriched fuel utilization, essential for reducing fossil fuel consumption and achieving carbon neutrality. However, comprehensive guidelines for safe operation across a wide range of parameters still need to be established. In this paper, numerical calculations are conducted to reveal the effects of H₂ enrichment and inlet velocity on flame behavior and combustion stability in an array micromix combustor. The results demonstrate that the combustor provides flexible combustion performance even under near-stoichiometric conditions, efficiently utilizing a wide range of fuels, including pure methane (CH₄) and pure H₂. Moreover, adjusting the equivalence ratio allows for low-emission performance. Blow-out of the H₂-enriched array flame starts at the outermost nozzle, and this behavior occurs under all inlet velocity conditions from 20 to 120 m/s. Based on this foundation, stability maps are constructed to illustrate the interdependence between the H₂ blending ratio and equivalence ratio, as well as the relationship between inlet velocity and equivalence ratio. The results indicate that higher H₂ enrichment expands the blow-out limit range. Two inflection points emerge in the blow-out limit curve during the transition from CH₄ to H₂. Additionally, increasing inlet velocity shifts the blow-out limit to higher equivalence ratios. However, this trend weakens as H₂ enrichment exceeds 80 %. A dimensionless Peclet model incorporating Reynolds number correction is proposed to predict flame blow-out limit curves, which offers assistance in design optimization for H₂-enriched fuel operating conditions to ensure the stability of array micromix combustors.