Hydrogen Fuel and Cooling System Promises Leap in Zero-Emission Aviation

By Muhammad OsamaReviewed by Laura ThomsonJun 10 2025

A recent study published in Applied Energy proposed an integrated framework for liquid hydrogen (LH₂) storage, thermal management, and transfer control for hybrid-electric aircraft. The system aims to improve fuel efficiency and balance hydrogen’s dual role as a propellant and coolant, addressing storage and thermal challenges in hydrogen-powered aviation.

The Promise and Challenges of Hydrogen in Aviation

Aviation significantly contributes to carbon dioxide (CO₂) emissions, making hydrogen a promising alternative due to its high energy density, 2.8 times greater than conventional kerosene, and clean combustion. However, its low ambient density complicates long-haul storage.

Hydrogen is stored as a saturated liquid (70.8 kg/m3) at cryogenic temperatures to improve storage efficiency. However, full storage, thermal management, and transfer control integration remain underexplored. The Integrated Zero Emission Aviation (IZEA) project focuses on short-range hydrogen-powered aircraft for environmental sustainability.

Introducing an Efficient Storage and Transfer System

Researchers have developed a hybrid-electric aircraft with a blended wing body design, capable of carrying 100 passengers. The aircraft is powered by hydrogen fuel cells, hydrogen-fueled combustion turbines, and high-temperature superconducting (HTS) electric generators.

This configuration enhances efficiency and reduces emissions by utilizing fuel cells during low-load phases (taxiing and cruising) and combustion turbines during high-load phases (takeoff), achieving a peak power demand of 16.2 MW.

In the aircraft’s prototype, LH₂ is stored in two symmetrically placed tanks near the centerline, connected to power components through counterflow pipe-in-pipe heat exchangers. These exchangers utilize supercritical helium or water as working fluids to cool systems operating between 20 K and over 300 K. Hydrogen absorbs heat before entering the fuel cells and turbines, enabling efficient energy transfer and system cooling.

Pressure Regulation and System Optimization

The study employs a novel pressure regulation strategy to maintain tank pressure slightly above the combined pressure drops across the heat exchangers and the optimal 1.3 bar fuel cell operating pressure, eliminating the need for cryogenic pumps.

Pressure is managed using hydrogen gas charging from compressed cylinders and vapor venting, with sensors providing real-time feedback to ensure stability during various flight phases.

The tanks feature an elliptical shell with half-ellipsoid end caps to optimize volume, wall thickness, and insulation, enhancing the gravimetric index (fuel mass vs. system mass). Aluminum alloy 2219 was selected for its strength and cryogenic performance, while closed-cell rigid polyurethane foam minimizes heat ingress during a 120-minute ground hold.

Heat exchangers were sized using thermal-fluid models based on temperature-dependent properties, cooling loads, and pressure constraints. System-level optimization considered vent pressures and component masses to maximize efficiency, addressing key challenges in hydrogen storage, thermal regulation, and safe delivery for zero-emission flight.

Optimized Performance: Fuel Efficiency and Thermal Regulation

The optimization showed that the maximum overall gravimetric index of approximately 0.62 was achieved at a vent pressure of 1.63 bar, slightly above the optimal pressure for the tank alone (1.36 bar). This shift highlights the importance of system-level integration, as lower tank pressures necessitated larger, heavier heat exchangers, ultimately reducing efficiency.

The system's mass breakdown indicated that LH₂ fuel accounted for 54.7% of the total system mass, followed by tank walls at 25.4%, insulation at 3.2%, heat exchangers and their insulation at 3.4%, working fluids at 1.4%, and cryogenic fans and pumps at 11.9%. Tank wall and insulation thicknesses were optimized to fit within the aircraft’s fuselage constraints.

Heat exchanger designs were tailored to specific component requirements, with inner pipe diameters ranging from 3.3 cm for initial hydrogen warming to over 7 cm for fuel cells operating near 333 K. Pressure drops across exchangers were controlled to maintain tank pressure during peak flow at takeoff. The system incorporated commercially available cryofans and pumps to drive working fluids efficiently with minimal added mass.

Tank pressure regulation simulations confirmed the system’s ability to manage tank pressure dynamically through gas charging and vapor venting during all flight phases, including a 40-minute taxi-out and rapid power ramp-up scenarios. Due to lower ambient temperatures, heat leakage rates decreased at cruising altitude, and vented hydrogen vapor was proposed to be redirected to fuel cells, minimizing fuel losses.

Applications in Next-Generation Aerospace Technology

The integrated LH2 storage and thermal management system significantly advances aviation. It enables efficient hydrogen storage and thermal control, supporting the development of hybrid-electric aircraft that meet environmental standards without compromising performance or safety.

Using LH2 as fuel and coolant simplifies design and weight considerations. Modular heat exchanger loops with dedicated working fluids allow for independent thermal regulation of components, addressing compatibility and thermal shock concerns.

Initially developed for regional aircraft, the system demonstrates scalability for long-range operations and facilitates integration across various aircraft configurations. Beyond aviation, this technology has potential applications in maritime and heavy-duty transport sectors.

Toward Zero-Emission Aviation

This research marks a significant step toward zero-emission aviation by integrating LH2 storage, thermal management, and transfer control. It demonstrates a scalable solution for hybrid-electric aircraft by optimizing hydrogen’s dual role as a propellant and coolant. The findings highlight the significance of system-level optimization in regulating hydrogen flow, laying the groundwork for sustainable aircraft design and clean aviation technologies.

Future work should enhance heat exchanger efficiency, particularly for cooling fuel cell stacks that generate substantial heat. Refining thermal management and optimizing system architecture, including fuel storage, transfer mechanisms, and superconducting components, will further improve the feasibility of hydrogen-powered aviation. These advancements are essential for developing commercially viable zero-emission air transport.

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