Preliminary design, integration and evaluation of a liquid-based thermal management system for fuel cell hybrid aircraft

The growing demand for sustainable aviation has driven significant interest in hybrid-electric propulsion systems, particularly those incorporating hydrogen fuel cells due to their high specific energy and zero carbon emissions potential. This thesis aims to fill a significant gap in evaluating fuel cell hybrid-electric aircraft: the design and integration of an effective Thermal Management System (TMS) that can maintain optimal operating conditions while minimizing its impact on aircraft performance.Focusing on a general aviation case study, this research proposes a methodology for the preliminary design, integration, and evaluation of a liquid-based TMS tailored to low-temperature Proton Exchange Membrane Fuel Cells (LT-PEMFC) within this hybrid-electric propulsion framework. Operating within the constraints of a retrofitted aircraft architecture, specifically the Daher Kodiak 900, the study addresses the challenges of integrating such systems into an existing airframe.A comprehensive multidisciplinary design and optimization (MDAO) framework is developed using the FAST-OAD simulation platform, extended to include TMS-specific modeling. Component-level models are gathered and/or derived to represent the TMS. Additional components are also included to adequately reflect the fuel cell’s integration within the defined scope. A hybridizationstrategy and representative flight profile are defined to establish the operational context for the fuel cell and its TMS. The integrated framework captures interactions between thermal loads, volumetric constraints, aerodynamic drag, and other aircraft-level trade-offs. The objective of the proposed framework is twofold: firstly, to serve as a toolset for preliminary feasibility assessments, and secondly, to lay the groundwork for a scalable modeling and evaluation approach to TMS design that can be applied to other case studies and/or power requirements.The study yielded the following results for the Kodiak 900 with a 200 kW fuel cell operating during cruise phase only. The final fuel cell system (including its TMS) has a mass of 307 kg and occupies approximately 1.344 m3. Compared to the conventional internal combustion engine (ICE) configuration, the hybridized version yields a reduction of 183 kg in CO2 emissions over a 300 NM mission, but this comes at the cost of a 263 kg reduction in available payload. The resulting emission per-passenger gain is therefore limited to less than 2% . When comparing the emissions per kilogram of available payload, the conventional ICE configuration outperforms the hybridized version. Asensitivity analysis conducted at the aircraft, fuel cell, and TMS level showed that even with the most favorable design parameters, performance improvements remain modest and the conventional ICE aircraft retains an overall advantage. Lastly, a hypothetical scenario implementing the fuel cell without its TMS leads to overly optimistic conclusions, thus highlighting the importance of accurate TMS modeling and consideration. In this regard, the thesis makes a significant contribution by proposing a methodology for sizing a liquid-based TMS applied to LT-PEMFCs.