Non-Eroding PCM Composite Nozzle

The extreme environment of a rocket nozzle has high velocity hot combustion products that will erode an uncooled throat area. When the nozzle temperature is high, physical and chemical processes will erode even the most refractory materials such as tungsten, carbon and carbide ceramics. Modern hybrid rockets pose especially challenging problems because of higher combustion temperatures and potential mixing instabilities. Because such erosion degrades rocket performance significantly, there is high payoff in developing non-eroding materials concepts for use in both tactical and launch vehicle rocket motors. Cooling is a known effective means of eliminating nozzle erosion in liquid propulsion rockets, but the traditional implementation of cooling is complex and impractical for other rockets. This project investigates a simple configuration for a cooled composite nozzle in which transpiration cooling arises from the volatilization of phase-change materials (PCMs) that saturate a porous structural matrix. The proposed matrix is a novel non-woven refractory fiber structure that allows control of porosity, strength, conductivity and capillary retention. The proposed concept is expected to outperform phenolic ablators because there are numerous PCMs condidates that can provide adequate cooling when the vapors transpire at the surface and the structural matrix is far more resistant to erosion than the char arising from ablators. Phase 1 will evaluate a series of composite materials with different matrix material configurations and different PCMs including a metal and a salt. Small nozzles will be tested in a laboratory hybrid rocket configuration for burn times lasting tens of seconds. Modeling will address PCM vapor flow and thermal penetration in the nozzle throat area. The benefits for specific rocket motor applications will be assessed.