Effects of pulsed hydrogen injection on mixing and combustion performance in a supersonic flow field

An unsteady numerical method based on the Reynolds-averaged Navier-Stokes equations was developed to study the effects of a sine-wave pulsed-injection strategy on the hydrogen/airflow operating performance and flow structure (mixing and combustion process) in a supersonic flow field. In the numerical simulations, hydrogen was injected transversely into a supersonic flow field at different sine-wave pulse frequencies, after which it underwent mixing with the free stream and combustion. Compared with steady injection, it was found that pulsed injection can improve the mixing performance with its characteristic alternating high and low pressures, and different pulse frequencies were found to produce diverse effects. Additionally, the mixing length, which is related to the uniformity in the distribution of the hydrogen mass fraction, was found to be proportional to the penetration depth in the flow field. Both the mixing length and penetration depth of the fuel were found to be shortest at a pulse frequency of 5 kHz. Within a certain frequency range, a pulsed-injection strategy can modify the heat-release law, decrease the length of the pre-combustion shock train, and improve combustion performance. The penetration depth was found to be the greatest at a pulse frequency of 10 kHz, and this increased the thrust augmentation by 0.14%.