Challenges of Retrofitting Existing Aircraft With Next-Generation Powertrains

This study investigates the challenges and near-term limitations associated with implementing hybridization strategies in existing narrow-body aircraft, with a particular focus on mild parallel hybrid-electric architectures operating on alternative fuels, including PtL-SAF, LPG, LNG, and LH2. The analysis examines how fuel selection and limited electrification influence aircraft performance, emissions, and operational characteristics for a retrofitted Airbus A220-100 platform. A Latin Hypercube Sampling approach is employed to explore the design space and evaluate cost per revenue passenger-kilometer, hybridization trends, mission-level emissions, and turnaround time. For each configuration, onboard fuel and energy storage systems are resized within the constraints of the baseline aircraft outer mold line, accounting for mass and volume limits. Uncertainty in the medium-fidelity chemical reaction network used for combustor emissions modeling is quantified using a Monte Carlo simulation. The results show that the optimal hybridization strategy follows the inverse trend of engine specific fuel consumption, with increased electric assistance during takeoff and climb and minimal contribution during cruise. However, with current battery technology, the economic benefits of mild hybridization are limited, with cost reductions observed only for the LH2 configuration. Across all fuels, mild hybridization produces negligible changes in total mission CO2-equivalent emissions per revenue passenger kilometer. Operationally, turnaround times remain comparable to conventional narrow-body operations for all configurations, with battery recharging identified as the primary constraint. Overall, the findings provide system-level insight into the trade-offs and practical feasibility of retrofitting existing narrow-body aircraft with hybrid-electric and alternative-fuel propulsion technologies.