Trade-Space Assessment of Liquid Hydrogen Propulsion Systems for Electrified Aircraft

In this paper we assess the feasibility of turbo-, hybrid-, and fully-electric civil aircraft propulsion systems. A modular optimization framework was developed to quantify system performance for a single-aisle transport aircraft with a mission similar to a Boeing 737-800. Various propulsion systems leveraging superconducting motors, boundary layer ingestion, distributed electric propulsion, high-temperature PEM fuel cells, and liquid hydrogen fuel were examined for the same notional aircraft. Aviation turbine fuel (ATF) and liquid hydrogen were compared using the payload-fuel energy intensity, PFEI, the fuel energy required per product of range and payload. For a given mission, the PFEI of the hydrogen-fueled fully-electric configuration examined was 4% higher than the ATF-burning twin turbo-fan baseline but produced zero carbon dioxide or nitrogen oxide emissions during flight. Relative to this baseline, a hydrogen-fueled turbo-fan had 24% lower PFEI, an ATF-burning turbo-electric propulsion system had 8% higher PFEI, and a hydrogen-fueled turbo-electric propulsion system had 14% lower PFEI. For the chosen mission, PFEI increased when adding fuel cells to a turbo-electric system or batteries to a fully-electric, fuel-cell-powered system.