Effect of fill flow rate on flame acceleration in a detonation channel

In a pulse detonation engine, filling fresh reactive mixtures into the detonation chamber is an indispensable process. The fill flow rate would significantly influence the subsequent flame acceleration and detonation initiation processes. Nevertheless, the existing works regarding the flame acceleration and detonation initiation are mostly performed on the quiescent mixtures. This work, therefore, investigates the effect of fill flow rate on the flame acceleration process in a square cross-section, obstructed detonation channel. Ethylene was utilized as the fuel, and oxygen-enriched air with an oxygen volume fraction of 40% as the oxidizer. The flame acceleration processes of quiescent and moving mixtures were observed by high-speed Schlieren and chemiluminescence techniques. It was found in this work that the fill flow rate dominates the flame propagation in the early stage of the flame acceleration (i.e., to the sound velocity of reactants). The initial flame structures vary from smooth (quiescent) to wrinkled (50 g/min) and cellular (100 g/min and 150 g/min), and to turbulent (200 g/min) with the increase of the fill flow rate. The Schlieren measurements of the filling processes show that the flow instabilities and the shear layer shedding from the obstacle surfaces into the mainstream are responsible for the promoted flame acceleration in high fill flow rate cases.