On the propagation stability of droplet-laden two-phase rotating detonation waves

Abstract

The propagation characteristics and stability of droplet-laden two-phase rotating detonation waves are studied by theoretical analysis and numerical simulations. The stability criterion of rotating detonation waves is proposed for an annular combustor fueled by liquid kerosene, which combines the pre-evaporation equivalence ratio φpre and a dimensionless parameter Δ. The latter one is defined as the ratio of the droplet evaporation distance LE to the detonation wave front height LD. The maximum droplet diameter as well as the stability boundary for the rotating detonation wave without pre-evaporation is found theoretically. Furthermore, numerical simulations are conducted on the two-phase rotating detonation waves produced by kerosene droplets and high-temperature air by means of the Eulerian-Lagrangian method. The effects of initial droplet diameter d0 and φpre on the propagation characteristics of rotating detonation waves are analyzed. The mechanism of detonation instability and wave-quenching as d0 and φpre exceed the stability boundary is explored. Results show that for φpre = 0, the droplet evaporation becomes longer and the rotating detonation wave tends to be less stable as Δ gradually increases. The unburned reactant pockets are generated at the detonation front and are consumed by the transverse detonation waves. When Δ is approximately equal to 1.0, the insufficient evaporation leads to the formation of local larger unburned reactant pockets. If the unburned reactant zones gradually enlarge, the flame and shock wave will be decoupled, and the detonation quenched soon. Increasing φpre can significantly improve the propagation stability of detonation wave for Δ ∼ O(1.0). The stability regime of droplet-laden two-phase rotating detonation waves is obtained and the above stability criterion is verified based on the simulation cases. The conclusion will inspire the optimization design of the liquid-fuel rotating detonation engine.