Very High Altitude Aircraft Propulsion Engines

Firestar Engineering, LLC has been exploring the use of NOFB monopropellants for use in very high altitude unmanned aerial vehicle applications. Monopropellants remove the requirement for ingesting air into the vehicle. As a result, the feed system is greatly simplified, and there is no requirement to reject the large quantity of waste heat at altitude that accompanies large compression ratio air compressors. Furthermore, the combustible inflatable that can be readily derived from the primary NOFB feed system tank can be used for many additional supporting functions such as decelerator deployment, wing and prop inflation/rigidization, and operational self-destruct options. In our Phase I research, we have demonstrated utilization of an NOFB monopropellant in a single piston engine that has been run to monopropellant exhaustion allowing the engine to achieve full thermal equilibrium. In our Phase II proposed work, we’ll focus our efforts on higher energy density monopropellants designed specifically for piston engine operation as well as engine modifications for improving the overall thermal energy conversion efficiency of the piston engine.