Effects of flow rate and fuel/air ratio on propagation behaviors of diffusion H2/air flames in a micro-combustor

A Y-shaped micro combustor consisting of three quartz tubes with an identical inner diameter of 2.0 mm was designed. Effects of total flow rate and fuel/air ratio on the propagation behaviors of non-premixed hydrogen-air flames were investigated experimentally. Six distinct modes were observed, including flames with repetitive extinction and ignition. Noise emission was detected during flame propagation towards upstream under relatively high mixture velocities. The mean flame propagation speed decreased monotonically with an increasing mixture velocity, however, it exhibited a non-monotonic variation with the nominal equivalence ratio and peaked at ϕ = 0.9. Stable edge flames were obtained at the intersection under suitable conditions, and its length increased as the mixture velocity was increased, but varied non-monotonically with the nominal equivalence ratio and had a maximum value at ϕ = 0.9. The regime diagram of the six flame propagation modes was drawn, which can provide an overview of the relationship between the inlet condition and flame propagation mode. Qualitative analysis showed that flame dynamics of non-premixed micro-combustion was closely associated with the total flow rate and fuel/air ratio by influencing the mixing effectiveness, residence time, heat release rate and heat loss rate. •Diffusion H2-air combustion in a Y-shaped micro combustor was experimentally studied.•Six flame propagation modes were observed by varying flow rate and fuel/air ratio.•Flame with repetitive extinction and ignition was captured in diffusion combustion.•Stable edge flame can be established at the intersection under suitable conditions.•Flame regime diagram was drawn in the “velocity-equivalence ratio” coordinate system.