Effects of pulsed injection on ignition delay and combustion performance in a hydrogen-fuel scramjet combustor

This paper describes the pulsed injection of hydrogen fuel with an incoming Mach number of 2.5 in a directly connected pulse combustion wind tunnel. The hydrogen pulse injection test with 33 Hz–62hz frequencies was carried out by using a mechanical pulse injector.The effects of different injection frequencies on the ignition delay and combustion performance of the hydrogen fuel are analyzed by means of flame self-luminescence photography and wall pressure measurements, and the results are compared with those of steady injection. The results shows that there is an optimal pulsed injection frequency--39 Hz in the frequency range studied in this paper, at this frequency, the ignition delay of hydrogen is much shorter than that of steady injection.In addition, the study also found that pulsed injection improves the combustion performance of hydrogen, so that the energy released by hydrogen combustion at lower equivalence ratios is equal to that released by steady hydrogen injection at a higher equivalence ratio. For both pulsed and steady injection, the development of the hydrogen flame can be attributed to the propagation theory of diffusion flame. The pulse frequency is not observed to have any significant effects on hydrogen combustion performance.