Experimental Study on Combustion of Water Vapor and Aluminum Powder for Chemical Micropropulsion

A combination of water and aluminum powder has been studied for space propulsion. These propellants are particularly suitable for chemical micropropulsion. However, development is being delayed due to many constraints, mainly: safety requirements and system restrictions. This study measured the combustion pressure and reacted aluminum fraction of pulsed combustion using water vapor and aluminum powder under conditions that satisfy the following constraints: water vapor pressure under 100 kPa, aluminum powder diameter over 10 mu m, and a combustion chamber smaller than 1 L. In the experimental combustion chamber, the water vapor flow had a mass flow rate of 23.3 mg/s and a velocity of 1.6 m/s. The aluminum powder was lifted and mixed with the nitrogen gas and injected into the water vapor flow and ignited by a spark. The result was organized using an oxidizer-to-fuel ratio in the combustion chamber. When the ratio was around 0.5, the maximum pressure and reacted aluminum fraction marked significant values for micropropulsion: 191.6-313.4 kPa and 0.18-0.36, respectively. The results revealed that the nitrogen gas promoted combustion by diffusing the powder rather than suppressing it, and the importance of the controlling powder diffusion and the ignition timing.