Experimental study of atomization effects on two-phase pulse detonation engines

This article presents some results dealing with effects of atomizer types on mean droplet size and pulse detonation engine (PDE) performance. The plain-orifice injector and twin-fluid air-assist atomizer were located at the head-end of a PDE mockup to inject gasoline, which was used as the liquid fuel. A particle size meter based on laser light scattering was employed to measure mean droplet size. The curves of mean droplet size versus gasoline flux and gasoline/air ratio are obtained. The twin-fluid air-assist atomizer can produce much smaller mean droplet size than the plain-orifice injector. The air was injected into the mixing chamber through tangential ports that gave the fuel a high angular velocity, thereby creating smaller droplets. To observe the effect of gasoline droplet size on PDE, the proof-of-principle experiments of PDE were carried out. The experimental results indicated that the equivalence ratio lower limits decreased and the upper limits increased as the gasoline droplet size decreased when air-assist atomizer was used instead of plain-orifice injector. That meant the equivalence ratio limits turned wide as the gasoline droplet size decreased. Meanwhile, the optimum equivalence ratio decreased as the gasoline droplet size decreased. The smaller the droplet size, the lower the optimum equivalence ratio required to stabilize detonation. As the operation frequency increased, the equivalence ratio limit became narrow and the difference of optimum equivalence ratio between the air-assist atomizer and the plain-orifice injector decreased. Furthermore, droplet size of liquid fuel had a considerable effect on the wave speed. The wave speed increased as the gasoline droplet size decreased, while still being lower than the gas-phase Chapman-Jouguet detonation velocity.