Advanced Conceptual Design Studies on a Hydrogen-Hybrid Dual-Fuel Regional Aircraft Retrofit

Current research in commercial aviation is exploring numerous propulsion and aircraft technologies to mitigate its environmental impact. While purely hydrogen-powered aircraft face manifold challenges, combining hydrogen and conventional fuel may facilitate the introduction of hydrogen-based flight. This study outlines the conceptual design of a parallelhybrid dual-fuel regional aircraft retrofit based on the D328eco under development by Deutsche Aircraft. The assessed retrofit approach aims to extend airframe service life and reduce emissions by incorporating a propulsion system designed for future requirements. By integrating high-temperature polymer-electrolyte fuel cells (FCs) to assist conventional turboshaft engines burning sustainable aviation fuel (SAF), the powertrain reduces SAF consumption. Retrofit assumptions retain maximum takeoff mass and center-of-gravity location while reducing payload (PL) to accommodate the propulsion system mass increase. Utilizing the Bauhaus Luftfahrt Aircraft Design Environment BLADE, various aircraft-level sensitivities and hybridization strategies were assessed. The SAF/PL ratio was identified as a key metric, and enabling FC support during diversion climb shifted its minimum from a 20.3% to a 37.2% hybridization degree, while enforcing the imposed payload, liquid hydrogen tank length, and diversion climb time limits. Retaining the reference turboshaft-engine for reduced retrofit development costs, a hybridization degree of 20.2% was attainable while the minimum allowable payload was carried aboard. Subsequent off-design mission analysis revealed a decrease in transportation performance for reduced mission ranges, underlining the importance of market-tailored aircraft designs, especially for heavier and thus less performant retrofits. The main studies were complemented by a higher-level emission and climate impact assessment to set the basis for more generalized retrofit statements.