Experimental study on the propagation characteristics of non-premixed H2/air flames in a curved micro-combustor

In this study, propagation characteristics of non-premixed H2/air flames in a curved micro-combustor were experimentally investigated. It was found that after cold-state ignition at the combustor exit, flames can propagate upstream and form a stable flame over a wide range of average inlet velocity (Vave,in) and nominal equivalence ratio (φ). The top-wall temperature distribution demonstrated that a flame separation phenomenon occurs when φ ≤ 1. High temperature zone of the combustor wall expanded and shifted downstream with an increasing Vave,in; however, with an increase in φ, it expanded initially and then shrank, and moved toward the air-side. The maximum wall temperature varied non-monotonically with both the Vave,in and φ, and they peaked at Vave,in = 1.5 m/s and φ = 1.6, respectively. Both lower and upper propagation limits (i.e., propagable velocities) exhibited non-monotonic tendencies versus φ. Specifically, the lowest and highest propagation limits are 0.3 m/s and 7.0 m/s, respectively, and they both occur at φ = 1.4. Empirical correlations of the propagation limits and propagable velocity range with φ were obtained. In summary, the present study demonstrated the feasibility of cold-state ignition of non-premixed H2/air for curved micro-combustors, and revealed the main flame propagation characteristics.