ToffeeX, part of the Hyfan consortium, has successfully designed an air-cooled hydrogen fuel cell system for a drone’s nacelle, solving one of the system’s toughest engineering problems—thermal management in tight spaces. Cooling hydrogen fuel cells in drones remains a key barrier to scaling zero-emission UAVs for real-world, commercial deployment.
We knew from the start that this compact configuration would bring cooling challenges. Directing uniform airflow through narrow nacelle geometries is no simple task. By engineering the airflow path from the beginning of the design process, we prevented uneven distribution and thermal failures before they could start.
The results of this project show that air-cooled hydrogen fuel cells (HFC) can succeed in space-constrained platforms—if the airflow is designed with precision.
Here’s how we made it work.
The problem: getting air where it needs to go
HFCs offer a clean, high-energy-density solution for next-generation flight. But fitting them into compact aerial platforms like drones introduces severe thermal constraints.
In air-cooled PEM fuel cells, forced air passes through narrow cooling channels between cell layers. But forcing air in isn’t enough—the flow must be uniform. Non-uniform flow can lead to localized hotspots, uneven reaction rates, and degraded cell life.
Hydrogen-powered flight with a packed-in fuel cell
The HyFan Consortium, backed by Innovate UK, was an 18-month project focused on ensuring thermal management for air-cooled HFCs is as effective and compact as possible, helping to maximize payload capacity in zero-emission unmanned aerial vehicles (UAVs).
What made the project unique was the requirement to fully integrate the HFC within the nacelle—the streamlined housing typically used to enclose propulsion systems and critical onboard components. This tightly packaged design creates an extremely challenging thermal environment, where airflow has to be precisely controlled throughout every twist and contour.
Thermal rejection can exceed 1.5 kW for a 3 kW fuel cell system. The cooling strategy involved bleeding air from the engine and directing it toward the fuel cell. However, guiding airflow through sharp bends and tight nacelle geometries posed a significant challenge, especially when uniform distribution across the cooling channels was essential for reliable performance.
The breakthrough: targeted velocity objectives
ToffeeX was pivotal in addressing this challenge through its generative design platform, tailored for advanced thermal-fluid systems. Rather than focusing solely on minimizing pressure loss, ToffeeX enables engineers to define target flow conditions within the design space, including velocity and direction.
This approach was especially valuable in the HyFan program. ToffeeX generated geometries that directed airflow to where it was needed by specifying desired airflow within critical regions of the cooling domain, even through sharp bends and compact nacelle-like spaces.
To validate the designs, ToffeeX ran a series of reduced-scale laboratory experiments. These tests confirmed the simulations’ predictions: flow was evenly distributed across the intended paths, with improved thermal uniformity and performance reliability.
This approach flips the script on traditional cooling design—rather than correcting airflow issues after they happen, it starts by shaping the flow exactly where it needs to go. It’s a game-changer for HFCs and other tightly packaged systems where every bend and channel matters.
Simulation + experiment: rapid iteration with real-world feedback
ToffeeX’s software enabled rapid design iteration, significantly accelerating development compared to traditional, often manual, design methods. Early-stage models used simplified representations, such as treating the fuel cell as a porous domain, allowing engineers to quickly explore design directions and identify problem areas without heavy computational overhead.
As confidence in the design grew, the same workflow supported incremental increases in model complexity, progressively refining detail and fidelity. This stepwise approach made it easy to learn from each iteration, improving both speed and insight.
ToffeeX also integrates manufacturing-aware design constraints tailored to different production methods, including additive manufacturing. These constraints are built into the platform in a way that’s accessible to non-experts, making it easy to generate designs that are not only high-performing but also practical to build.
For the HyFan lab tests, the optimized components were fabricated using additive manufacturing, demonstrating that simulation-ready designs can translate directly into physical prototypes.
Thermal imaging and pressure measurements from the modular experiments confirmed that the optimized flow paths consistently improved the flow uniformity and reduced hotspots in critical regions.
A smarter way to cool compact systems
The HyFan program demonstrates that air-cooled hydrogen fuel cells can work in tightly constrained aerial systems, if airflow is intelligently designed. ToffeeX’s generative design opens the door to compact, high-performance cooling systems for aviation and beyond.
With system-level tests under our belts, we can now see that generative design and hydrogen technology can scale to real-world applications and take flight.
About the HyFan consortium
Greenjets
Developers of quiet, efficient electric engines for drones, air taxis, and regional aircraft.
Bramble Energy
Pioneers of scalable hydrogen fuel cells using their customizable PCBFC™ technology.
Aurata Technologies
Experts in thermal system integration and simulation for fuel cells and batteries.
Innovate UK
The UK’s national innovation agency, part of UKRI, supports breakthrough ideas to drive growth and sustainability.
