Experimental investigation on a two-phase valveless air-breathing pulse detonation engine

In order to achieve high-speed cruise capability in the atmosphere, revolutionary concept propulsion systems including air-breathing pulse detonation engine (PDE) are required. A valveless air-breathing PDE mockup was designed and manufactured, which was made up of subsonic inlet, mixing chamber, ignition chamber, detonation chamber and nozzle. The proof-of-principle experiments of PDE mockup without nozzle were carried out in order to observe the air inlet effect on pulse detonation. Liquid C₈H₁₆/alr mixture with no oxygen enrichment and automotive spark plug with ignition energy lower than 50mJ were used as propellant and one-step Ignition system respectively. The air was supplied upstream of the air inlet by a semi free flow field. The velocity of the air upstream of the air inlet can be regulated in order to simulate a subsonic flow field. A circumferential seam configuration collecting the inlet with mixing chamber was used to increase the mixing degree of C₈H₁₆/air and reduce the bad effect of air inlet on detonation initiation for detonation is difficult to initiate in the tube with two end open. The measured detonation wave pressure ratio is very close to that of C-J detonation and the valveless air-breathing PDE mockup is easy to initiation. The deflagration-to-detonation transition (DDT) and two methods to reduce DDT distance were also investigated by experiments. The results indicated the DDT distance was about 1.3m (from the spark plug) and it was reduced to 1.09m when the ignitor with higher energy of 4.2J was used. And DDT distance did not show any significant dependence with the turbulence-increasing orifice plate. Compared to detonation tube or pulse detonation rocket engine (PDRE) with one end close and one end open, the evolution of pressure at different positions along the valveless air-breathing mockup is more complicated with twice rising and twice trailing.