Experimental Investigation on Aluminum-Based Water Ramjet for Propelling High-Speed Underwater Vehicles

Major challenges in developing and realizing a novel aluminum-water reaction-based water ramjet propulsion system for high-speed underwater vehicles and demonstration of a water-breathing jet propulsion test facility are investigated. Two stages of combustion, propellant grain combustion and subsequent water combustion, with primary combustion products are adopted. High-pressure-molded propellant grains up to 45% of micro-nano (50 & COLRATIO;50) aluminum were prepared and combusted in the primary chamber, which exhibits mild ignition delay, and a residue of 4-6% was retained. Once water is injected into the secondary chamber, the net thrust generation is increased more than twice from the exhaust jet and improves the specific impulse by 40%. The lean fuel conditions in the secondary chamber lead to reduction in combustion propensity, which causes drop in C* efficiency. The ultrafine iron-oxide-catalyzed micro-nano blended propellants marginally improved the propulsive performance than the uncatalyzed compositions. The C* efficiency of the catalyzed propellants was enhanced up to 38.6%. Aluminum agglomeration in primary combustion considerably occurred; apparently, only a fraction of aluminum particles or agglomerates are completely burnt within the secondary chamber, and the remaining aluminum particles are either partially burnt or go unreacted.