PIASECKI AIRCRAFT CORP — Department of Defense STTR Phase I: AFX20D-TCSO1

Description

eVTOL platforms, require energy storage and conversion systems with energy densities greater than 500Wh/kg that can be FAA certified and available within the next 3-5years. Lithium Ion (Li) Battery energy density (200Wh/kg) is currently inadequate, and anticipated future growth is uncertain. Hydrogen HTPEM Fuel Cells show potential for greater than 1000Wh/kg and address shortfalls of existing low temperature fuel cell performance, reliability, and affordability. Fuels cells have been successfully demonstrated in UAS applications. The proposed STTR intends to leverage results of ongoing IRAD funded HTPEM Fuel Cell research to model, test and confirm the feasibility of developing a certifiable HTPEM Fuel Cell architecture for the PA-890 and other manned eVTOL applications. In particular, the program intends to study the Turbo air-cooled High Temperature Proton Exchange Membrane (HTPEM) fuel cell power system configuration. This design allows to maximize the power output of a PEM fuel cell stack without adding significant 'parasitic' mass related to liquid-cooling. The idea is to deploy the open-cathode PEM FC stack in an air duct where pressurized (turbo), humidified and thermally stabilized air is circulated by means of fans. The compression of air is maintained (2-3 bars) inside an air duct by means of a compression system. The air duct is provided with a controlled throttle valve for partial discharge of air with reduced oxygen content (12%-16%). Discharged air is replaced with fresh compressed air with normal oxygen content. Thermal stabilization and humidification of air is provided by its recirculation. Water produced by fuel cells supports 100% relative humidity of circulated air. Condensed water is disposed of with discharged air. This technology provides the following advantages in comparison with lithium batteries: 5x higher energy density, 10x faster charging (5-15 min. vs 2 hours), lower fire risk. In comparison with traditional fuel cell systems the proposed technology provides 3x higher specific power, low environmental susceptibility, lower requirements for hydrogen quality offering lower operational cost; simpler design with fewer parts for higher reliability, lower acquisition and maintenance cost; mature component technology. Phase I will focus on: Develop mathematical models of the HTPEM fuel cell stack and of the complete fuel cell power system including the auxiliary systems to identify relevant sizing and evaluate performance in relation to several mission profiles of the PA890 eVTOL aircraft. Validate models with small-scale testing of fuel cell stack to confirm performance and assess aging. Define system architecture and development plan for Phase II, including design, manufacturing, assembly and testing of full-size 0.5MW-class fuel cell power system for PA890 eVTOL.