Conceptual Study of 80-Pax Fuel Cell-Driven Aircraft for Sustainable Aviation ^†

Abstract

The growing need to reduce aviation’s carbon footprint and reliance on fossil fuels has prompted the exploration of alternative propulsion technologies. Fuel cell (FC) systems offer a sustainable solution, generating only water vapor as a by-product. This paper presents a conceptual study, focusing on subsystem integration and safety aspects, for an 80-passenger, hydrogen-powered aircraft developed within the European Union (EU) co-funded NEWBORN (NExt generation high poWer fuel cells for airBORNe applications) Project. The designed configuration incorporates wing-mounted pods housing fuel cells, an electric motor, an inverter, a Thermal Management System (TMS), and Balance of Performance (BoP). This configuration is an effort towards environmentally friendly solutions, addressing climate change and paving the way towards greener aviation.

1. Introduction

For decades, the aviation industry has played a key role in global transportation, enabling the movement of both people and goods across vast distances with unequaled efficiency. Unfortunately, the aeronautic sector is also playing a significant role in climate change, accounting for approximately 2.5% of global carbon dioxide (CO₂) emissions and contributing about 4% to global warming due to additional factors like non-CO₂ emissions and contrails [1,2,3,4]. The increasing pressure from governments, environmental organizations, and public opinion to face climate change and achieve net-zero emissions forces the aviation sector to urgently find innovative and sustainable solutions to reduce aviation impact on global warming.

Several technologies are under evaluation and development. In particular, FCs have emerged as a promising candidate for aviation decarbonization, since they generate electricity using hydrogen as a fuel source by means of an electrochemical process, producing only water vapor as a by-product [5]. Thus, FC-driven aircraft have the potential to complete their mission of producing zero emissions, meeting both environmental and operational demands. Small aircraft have been successfully demonstrated (e.g., Boeing Fuel Cell Demonstrator [6], DLR (Deutsches Zentrum für Luft- und Raumfahrt) HY4 [7], and ZeroAvia’s Piper M-Class [8]), but the scalability to commercial aviation is not straightforward [9].

The present paper summarizes a conceptual study of an 80-passenger aircraft powered by fuel cells, designed to achieve sustainable and emission-free aviation. The activities have been carried out within the EU co-funded research project NEWBORN [10].

2. Literature Review

2.1. Overview of Sustainable Aviation Efforts

Aircraft decarbonization is a critical priority [11] for both the scientific and industrial communities, since the aviation sector is one of the fastest-growing contributors to greenhouse gas emissions [12,13]. Due to the demanding targets set by the European Green Deal [14], the aviation sector faces significant challenges, which can be addressed only by leveraging Research and Innovation (R&I) activities. R&I in Europe’s current status can be found in [15], which focuses on emissions reduction in aviation and offers insights by conducting a comprehensive assessment of aviation research projects, particularly those aimed at reducing emissions, and includes an in-depth analysis of specific research topics.

Research studies have identified several strategies for reducing aviation’s environmental footprint, including the development of biofuels, electric propulsion systems, and hydrogen-based technologies [16,17]. Each one of the proposed approaches offers unique benefits, but fuel cell-based propulsion systems have the opportunity to potentially offer zero-emission operations and high energy efficiency [18,19,20].

In the framework of the NEWBORN project, it has been decided to focus on the FC propulsion system for an 80-pax regional aircraft.

2.2. Advances in Fuel Cell Technology for Aviation

In recent years, FC technology has evolved significantly, driven by advancements in materials science and engineering. In particular, significant progress has been made in the improvement of Proton-Exchange Membrane Fuel Cells (PEMFCs), which are particularly well-suited for aviation applications due to their high power density and quick startup capabilities [21,22]. In addition to the FC technology improvement, the development of lightweight hydrogen storage systems has allowed us to explore the feasibility of integrating FCs into regional and commuter aircraft [23,24,25].

Demonstration projects (e.g., HY4 aircraft and H2Fly initiatives [26]), provided valuable insights into FC technology opportunities and challenges in real-world operative scenarios.

2.3. Challenges in Implementing Zero-Emission Aircraft

Despite promising progress in the FC technologies for aviation development, some obstacles persist in adopting fuel cell-powered aircraft on a large scale. Key challenges include developing hydrogen production, storage, and distribution systems [27,28].

Furthermore, the integration of fuel cells into aircraft designs requires overcoming engineering constraints related to weight, thermal management, and reliability [29].

Additionally, regulatory and certification frameworks for hydrogen-powered aviation also need to be established to ensure safety and operational feasibility [30,31].

3. Conceptual Design of the 80-Passenger Fuel Cell Aircraft

3.1. Aircraft Specifications and Mission Data

The NEWBORN Project focuses on two different aircraft categories: Certification Specifications 23 (CS-23) [32] for 19-passenger (pax) and Certification Specification 25 (CS-25) [33] for 80-pax categories.

The present paper describes the CS-25 80-pax configuration. The proposed configuration is a high-wing mounted design, with a T-tail configuration, featuring four electrical motors and FC systems housed in four pods (two per half-wing).

The aircraft’s main characteristics are reported in Table 1. Figure 1 shows the aircraft design mission in terms of the mission profile, power source usage, reserves, and efficiency.

Table 1. The aircraft’s main characteristics.

Parameters	Unit	Value
MTOW (Max Take-Off Weight)	kg	39,842
Airframe mass	kg	19,523
FCPSS (Fuel Cell Power Supply System) mass	kg	6000
Battery mass	kg	1317
Power electronics mass	kg	2368
LH2 (Liquid Hydrogen) tank mass	kg	1389
LH2 (fuel) mass	kg	845
Wing surface area	m2	113.8
FCPSS power available @ MSL (Mean Sea Level)	kW	7200
Battery power available	kW	1976
Shaft power available @ MSL	kW	7969
Technology
FC specific power	kW/kg	1.200
Battery-specific power	kW/kg	1.500
Battery-specific energy	kWh/kg	0.250
LH2 tank GI (Galvanized Iron)	/	0.378
Power electronics specific power	kW/kg	3.360
Power electronics efficiency	/	0.918

Figure 1. (a) Aircraft design mission and main dimensions. (b) Aircraft view and main dimensions.

3.2. Aircraft Architecture and Configuration

The aircraft has two pods per half wing, each one with a total net power of 2.4 MW. Each pod houses (Figure 2) 2 × 5 FCs superstacks of 0.4 m³, and 4.16 m³ BoP, which consists of an air line, an Anode Recirculation Loop (ARL), a DC/DC (Direct Current/Direct Current) converter, a control system, a High Voltage Junction Box (HVJB), and TMS without Heat Exchangers (HXs).

Figure 2. (a) Fuel Cell Power System (FCPS), and (b) integrated representation of FCPS within NEWBORN 80-pax aircraft.

Each pod has two rectangular radiators, each one 3.6 m², tapered towards the rear pod structure to reduce aerodynamic impact. The radiator air intake has a U-shaped design to minimize the aerodynamic impact on the wing. The engine mount has been designed on the basis of previous experience to house BoP, FCs, the electric motor (gold in Figure 3), the inverter (silver in Figure 3), and the electric motor TMS (pink in Figure 3).

Figure 3. (a) Pod external shape, (b) U-shaped inlet, and (c) pod components.

The battery system has a power density of 1.5 kW/kg, an energy density of 0.25 kWh/kg, and a volume of 2.7 m³. It is installed in the aircraft’s belly (Figure 4).

Figure 4. (a) Aircraft batteries (brown) and TMS (purple), (b) battery installation in the aircraft.

The tank system (see Figure 5) consists of two cryogenic low-pressure double-layer composite tanks with volumes of 18.4 m³ and 3.7 m³, housing a total LH2 volume of 845 kg.

Figure 5. (a) LH2 fuel tanks and venting system, (b) tank installation in the aircraft.

4. Safety Aspects: Hydrogen Leakage, Ventilation, and Venting Related

The purpose of this section is to present preliminary analyses, mainly based on engineering judgment, of aircraft and system safety, with a focus on hydrogen leakage, permeation, and the venting exhaust location. It introduces the ventilation concept used for the aircraft sections holding the hydrogen-related equipment. This section will examine potential failures of hydrogen-carrying systems and the mitigations currently in place.

The subsystems assessed are: the FC stack, hydrogen distribution, and hydrogen storage.

4.1. Fuel Cell Stack

Minor hydrogen leakage does not significantly reduce safety margins thanks to proper ventilation in affected aircraft zones. Hydrogen monitoring ensures that the supply can be stopped if levels surpass safety thresholds. Redundant fuel cells and distribution lines prevent simultaneous failure. Independent monitoring and mitigations address subsystem failures, though pressure component ruptures may still occur. Material qualification and design safety margins are essential. In case of significant leakage, emergency procedures, including potential stack shutdowns, help prevent hydrogen accumulation, while remaining fuel cells maintain power generation.

Due to the fuel cells’ installation in a pod isolated from the passenger cabin, there is no risk of hydrogen intoxication to passengers in the event of a hydrogen leakage.

4.2. Hydrogen Distribution

Hydrogen distribution failures can lead to leakage in the aircraft’s hull or loss of hydrogen supply to fuel cells, with valve failures—particularly in water valves—risking pipe freezing. Unmitigated failures may cause hydrogen to accumulate in the hull, posing a fire hazard and potentially catastrophic consequences. Mitigations and safety measures to prevent hydrogen buildup in the event of failure are crucial.

Leakage may arise from valve failures, both external and internal, resulting in gaseous hydrogen accumulation within the aircraft. To counter this, proper monitoring and ventilation systems are established. Dual-walled vacuum-insulated pipes are employed to mitigate the risk of piping rupture, and the distribution lines are routed on the top part of the aircraft to minimize the risk of H2 cabin penetration. Minor hydrogen leaks pose no hazard without an ignition source; however, significant leaks require robust fire protection measures, including grounding, fire sleeves, and insulators.

A monitoring system will trigger emergency procedures to manage significant leaks, potentially including stack shutdown and hydrogen purging through a burst disk. Independent valve sets on each of the aircraft’s sides prevent total fuel cell power loss from a single failure. Hydrogen pressure is continually measured, enabling issue detection in pressure regulation. Multiple safety lines ensure safe pressure management, while fire ignition sources are insulated and grounded to avoid sparks, with the bay properly ventilated.

4.3. Hydrogen Storage

Pressure vessel failures can lead to significant hydrogen release into the aircraft, requiring a design to prevent such incidents. Major leak mitigation relies on dual hydrogen containment, achievable with dewar tanks or foam-insulated tanks that can include a hydrogen barrier with ventilation. Cracks and tears, arising from thermal cycles, are monitored through regular checks of the hydrogen system; scheduled parts replacement mitigates undetectable faults. Monitoring hydrogen pressure and concentration helps identify early cracks and leaks; temperature sensors enable rapid responses to potential leaks.

Inner tank electrical evaporator failures could mistakenly increase system pressure, quickly identifiable by pressure sensors that would relieve excess through safety valves. Lower pressure could diminish the hydrogen available for fuel cells, but redundancy exists with electric and passive evaporators. Safety measures activate if sensors malfunction or give erroneous signals, potentially leading to hydrogen purging or pressure reduction.

Structural damage could disrupt hydrogen conditioning and pressure regulation; multiple attachment points ensure the pressure vessel’s stability. Welding failures would trigger emergency responses via pressure and temperature sensors, safely depressurizing the tank to avert explosive conditions. Proper fueling protocols minimize hazards from refueling line failures, and overall, robust redundancy and monitoring systems are in place to prevent explosions or significant hydrogen leaks.

5. Conclusions

The paper summarizes the results obtained within the EU-cofunded research project NEWBORN, whose aim is to develop new regional aircraft with an LH2 propulsion system.

In particular, preliminary allocation studies of the propulsion system’s main components have been carried out together with preliminary safety aspects assessment to verify the feasibility of the proposed concept. The proposed configuration features fuel cells housed in four wing-mounted pods. The pods are designed to reduce the aerodynamic interference between them and the wing. In particular, to reduce blockage, the airscope are located in the rear part of the pods and their inlets are U-shaped. Internal pod components (ARL, air lines, BoP, DC/DC converter, control system, FCs, HVJB, HXs, TMS) are positioned to minimize the volumetric bulk, ensuring the most aerodynamically efficient shape possible.

Li-ion batteries are installed in the belly fairing.

Two cryogenic low-pressure double-insulation layer composite LH2 tanks located in the rear aircraft cone guarantee system redundancy.

As a baseline, it is safe to assume that the zones of the aircraft containing hydrogen shall be isolated and sealed from the zones with passengers, such that no hydrogen leakage could enter the cabin and represent a hazard for the occupants. Moreover, proper monitoring systems and the adoption of redundancy and safety measures, such as ventilation and purging lines, shall be in place to guarantee compliance with the accepted safety hydrogen levels.