Numerical investigation on combustion performances of premixed H2-air jet flames above a sudden expansion micro-nozzle

Our previous study demonstrated that divergent micro-nozzles designed for H 2 -fueled domestic gas stoves can achieve a higher flame temperature than conventional straight micro-nozzles, but are more susceptible to flashback. To address this safety concern, the present work proposed a sudden expansion micro-nozzle and numerically investigated partially premixed H 2 -air jet flames. A unique flame pattern consisting of dual flames with a smaller one inside the nozzle was identified. Besides, at large inlet velocities, the flame temperature at an expansion ratio ( γ ) of 1.4 shows a largest increase by 45.6 K compared to straight micro-nozzle. Moreover, the flashback limit decreases monotonically with an increasing γ . Specifically, the flashback limit drops from 5.0 m/s at γ = 1.2–3.0 m/s at γ = 2.0. Furthermore, the flashback limits of sudden expansion micro-nozzles show a largest decrease by 16.5 m/s compared to divergent micro-nozzles. Analysis demonstrates that a larger γ leads to a wider recirculation zone and a lower wall temperature, which diminishes the heat recirculation effect on the unburned mixture and reduces the flashback limit. The optimal expansion ratio range for practical applications is recommended to be γ = 1.4–1.8. Overall, the present study provides guidance to optimize the sudden expansion micro-nozzles for H 2 -fueled gas stoves.