Journal of Propulsion and Energy ISSN:2734-1887(Print) 2765-0049(Online) Free Open Access International Journal on Propulsion and Energy Science and Technology

A high-resolution numerical study is carried out to investigate the auto-ignition process of ethylene fuel injection in a direct-connect scramjet combustor. Present study cares about the detailed flow evolution and flame development during the ignition transient. A quasi-global kinetics mechanism, benchmarked against detailed kinetics mechanisms, is employed to model the chemical reactions of ethylene with air in a high-speed environment. Comparing with the hydrogen fuel, the ethylene fuel is more difficult for auto-ignition, regardless of the local temperature and pressure conditions in the flame-anchoring region. The ignition delay often exceeds the flow residence time, and external means are required to achieve self-sustained combustion. As a specific example, the present research employed the air throttling to make a gas dynamic blockage downstream of the combustor. The resultant increase in the flow temperature and pressure, as well as mixing enhancement by the flow speed reduction in the pre-combustion region, greatly improves the ignition efficiency and leads to a stable flame for a while even after the air throttling is deactivated.