Methodology for Assessing Retrofitted Hydrogen Combustion and Fuel Cell Aircraft Environmental Impacts

Hydrogen (${\mathrm{H}}_2$) combustion and solid oxide fuel cells (SOFCs) can potentially reduce aviation-produced greenhouse gas emissions compared to kerosene propulsion. This paper outlines a methodology for evaluating performance and emission tradeoffs when retrofitting conventional kerosene-powered aircraft with lower-emission ${\mathrm{H}}_2$ combustion and SOFC hybrid alternatives. The proposed framework presents a constant-range approach for designing liquid hydrogen fuel tanks, considering insulation, sizing, center of gravity, and power constraints. A lifecycle assessment evaluates greenhouse gas emissions and contrail formation effects for carbon footprint mitigation, while a cost analysis examines retrofit implementation consequences. A Cessna Citation 560XLS+ case study shows a 5% mass decrease for ${\mathrm{H}}_2$ combustion and a 0.4% mass decrease for the SOFC hybrid, at the tradeoff of removing three passengers. The lifecycle analysis of green hydrogen in aviation reveals a significant reduction in ${\mathrm{CO}}_2$ emissions for ${\mathrm{H}}_2$ combustion and SOFC systems, except for natural-gas-produced ${\mathrm{H}}_2$ combustion, when compared to Jet-A fuel. However, this environmental benefit is contrasted by an increase in fuel cost per passenger-km for green ${\mathrm{H}}_2$ combustion and a rise for natural-gas-produced ${\mathrm{H}}_2$ SOFC compared to kerosene. The results suggest that retrofitting aircraft with alternative fuels could lower carbon emissions, noting the economic and passenger capacity tradeoffs.