Theoretical And Experimental Study On Single Droplet Combustion Of Gelled Propellant

Gel fuel must be one of the most potential power sources in the future advanced propulsion systems by combining the advantages of liquid and solid propellants. However, there are many differences between gelled fuels and traditional fuels about their evaporation and combustion characteristics. Therefore, making deep research on gelled fuel combustion under high-pressure and elevated temperature environment becomes more important for efficient combustion. Theoretical and experimental studies have been performed in this paper.In the experimental research, a device for droplet combustion under different conditions was designed and established to simulate the falling droplets combustion process in the high pressure and high temperature environments for gelled fuel. The variation process of droplet diameter during combustion was recorded by a high-speed digital camera, including three different modes: suspended droplet, falling droplet, and hot plate. The laws about the droplet diameter development with time were determined by treating the pictures obtained from the gelled fuel combustion under different temperature and pressure conditions. Conclusions are drawn as bellows:(1) The main difference between organic gelled fuels and traditional fuels about the combustion process is the periodic expansion, rupture and jetting.(2) The results show that the lower pressure and the higher ambient temperature as well as the concentration of the oxidizer is, the faster of the combustion speed and the shorter the existing time for gelled fuel droplet will be.As for the theoretical study, a physical model of gelled fuel droplet combustion under high-pressure and high-temperature N2/O2 environment was established based on reasonable simplifications and presumptions, which simulates the combustion process of organic gelled fuel droplet. The relationship based on ignition delay, flame temperature and flame location with the initial droplet diameter, environment temperature and pressure has been numerically calculated. The results show that the combustion process develops by two periodically stages because of the existence of the gallant. During the first stage, a gel layer is formed on the droplet surface which prevents the steam from vaporizing and bubbles are formed inside the droplet. Then the bubbles grow up and rupture at the second stage, when the pressure inside them exceeds the stress of the layer.The theoretic and experimental results were analyzed and compared, and they agree well within the considered conditions.