Preliminary Sizing of Balance-of-Plant Systems for Liquid Hydrogen Fuel Cell-Electric Propulsion in Regional Retrofitted Aircraft

Abstract

The aviation sector faces growing pressure to reduce greenhouse gas emissions, while projections are suggesting that emissions could double by 2050 to account for increases in passengers. Liquid hydrogen fuel cell-electric (LH2FCE) propulsion offers a promising solution, with the potential to reduce climate impact by up to 90\% compared to conventional turboprop engines. However, significant challenges exist, including heat dissipation, increased drag, and increased weight penalties from heavy fuel cell stacks, cryogenic hydrogen storage and thermal management systems.
This thesis evaluates the impact on payload and range of retrofitting a regional turboprop aircraft with an LH2FCE propulsion system, by performing the preliminary design of the balance-of-plant systems, and assessing system performance by means of steady state analyses in take-off, top-of-climb and cruise conditions. A lumped parameter model was developed to simulate the fuel cell and balance-of-plant components, including an air supply and thermal management system and ram air ducts. Results show that payload reductions of approximately 58-77\% are expected for a 1500 km range compared to current turboprop aircraft, primarily due to increased mass and drag penalties, which reduce the propulsion system's specific power and lift-to-drag ratio. Sensitivity analyses were conducted, highlighting the effects of fuel cell operational parameters. It was revealed that adjustments in fuel cell temperature, pressure, and current density in the different operating conditions can enhance system performance. Additionally, it was found that most systems must be sized for top-of-climb, except for the ram air duct, which is constrained by take-off conditions. Incorporating a variable inlet design may eliminate ram air drag in cruise, although detailed drag analysis is recommended. Integration of a turbine and halving the rate-of-climb demonstrated that achieving a 1500 km range with a competitive payload (>3000 kg, 35 passengers) is feasible for retrofits, while reserving mass for non-modeled systems such as batteries. Moreover, projections for 2030 suggest that the performance of current turboprop aircraft could be matched by LH2FCE systems.
These findings highlight that LH2FCE propulsion is a viable and sustainable alternative for regional aviation, provided the reduction in payload is acceptable. With advancements in fuel cells, heat exchangers, electric motors, and liquid hydrogen storage, LH2FCE aircraft could achieve performance of current kerosene-powered turboprop aircraft by 2030.