Excessively Fuel-Rich Conditions for Cold Starting of Liquid-Fuel Pulse Detonation Engines

Cold starting a liquid-fuel pulse detonation engine with air as the oxidizer is always an unavoidable challenge because of the inherent insensitivity of droplet-air mixtures to undergo detonation initiation. The existing strategies are essentially attempts to accelerate the vaporization rates of liquid fuels to increase the amount of prevaporized fuel before ignition. In this paper, it has incidentally been discovered from experimental studies that a Jet A-1/air pulse detonation engine is able to operate successfully in relatively cold environments (mixture temperature at 70 degrees C) when an excessively fuel-rich mixture is used. The experimental results and theoretical phase equilibrium calculations show that the vapor-phase equivalence ratio is vital for successful detonation initiation spray detonations via a deflagrationto-detonation transition process. For a two-phase mixture containing a high overall fraction of fuel as compared with air, the amount of vaporized fuel achieves a stoichiometric or slightly rich composition, which is easier to undergo detonation. This discovery can potentially be applied for the simple startup of a liquid-fuel pulse detonation engine without incorporating any auxiliary systems.