Lift-off flames of propane under a variety of co-flow conditions

Abstract This study aimed at understanding the effects of co-flow condition on lift-off characteristics of the propane jet flame. A co-flow burner system was used to provide free jet condition, air co-flow condition and vitiated co-flow condition. In vitiated co-flow, methane was the co-flow fuel, and the co-flow equivalence ratios of methane/air mixtures changed from 0.5 to 0.7. On the basis of the results, the flame issuing into air-co-flow showed a higher lift-off height compared to the flame not issuing into a co-flow (i.e. free jet condition), with a faster increment rate simultaneously. In the vitiated co-flow condition, a conversion of lift-off height changing tendency was observed with the increment of flow rate and equivalence ratio of the co-flow. As the cases remained the same equivalence ratio, the cases with lower co-flow rates showed higher lift-off heights in the early combustion period. The lift-off height increased with the equivalence ratio in the cases with low co-flow rate, however, it decreased at high co-flow rate. It could be observed in the captured images that the ignition process was accelerated with the increment of equivalence ratio and co-flow rate.