Formation Analysis and Powderization of Combustion Products in a Magnesium-Wire and Water Micro-Hybrid Propulsion System

Micropropulsion systems using water as a propellant are suitable for rapid, low-cost development due to the high safety and availability of water. This study proposes a method to resolve the issue of magnesium oxide, the combustion product, growing to centimeter scale and degrading propulsion performance in the water-magnesium wire micropropulsion system, which has been proposed as a candidate to achieve 100 mN thrust and 100 s specific impulse. The proposed method involves applying vibrations to the magnesium wire during combustion to powderize the combustion products into sub-millimeter sizes. A powderization model was developed based on the wire’s vibration dynamics, and experiments were conducted by varying the input voltage and frequency of the vibration device. As a result, most of the combustion products were reduced to less than 1 mm, although some larger than 5 mm remained. As the frequency approached the resonance frequency of 403 Hz for a 31 mm wire, combustion time decreased. While combustion rate was independent of frequency, it tended to decrease with higher input voltage. Combustion amount was more closely correlated with combustion time than with combustion rate. At higher voltages, the Point drop phenomenon, where the combustion point is removed, occurred more frequently. Future research should focus on optimizing vibration conditions to further reduce the size of the combustion products and extend combustion time, thereby improving the overall powderization process.