Engineering consultancy Ricardo in the coming weeks hopes to select the fuel cell developer that will provide the power source for the electric conversion of a Britten-Norman BN-2 Islander it is working on as part of Project Fresson.
Led by Cranfield Aerospace Solutions (CAeS), the initiative, which is part funded by the UK government, aims to perform a first flight in late 2022, leading to the start of commercial operations by 2024.
While various suppliers to the project are already signed up, a recent switch from hybrid-electric to hydrogen power – which saw Ricardo brought on board – has meant that a fuel cell supplier has yet to be selected.
Ricardo is bringing together the fuel cell stacks and the required balance of plant – the pumps, valves, injectors, blowers, compressors, cooling systems and other equipment required for the cells to function – plus the management and control of the overall system.
But it has “engaged with multiple fuel cell stack suppliers” and is in a “down-selection process” and “approaching final nomination”, Andy Ennever, hydrogen fuel cells system service leader at Ricardo, said during a 19 May webinar.
As part of the overall design, the fuel cell stacks, balance of plant and the electric motors they power must fit inside the Islander’s existing nacelles.
Ennever says that Ricardo has come up with a “concept that meets Fresson’s requirements”, both in terms of each system’s size and other performance characteristics such as maximum power output of 250kW, rapid power response and overall efficiency.
“Through innovative design of the multi-stack balance of plant and intelligent control we are pushing the performance boundaries significantly for this system. And whilst the challenges will clearly live with us throughout the programme, at this point we are confident that the demonstrator requirements can and will be met.”
The concept should clear the preliminary design review hurdle in mid-June, followed by a critical design review in September.
“We are going through the process of procuring, assembling and testing ready for flight in the last quarter of 2022,” he says.
Dr Cedric Rouaud, global technical expert for thermal systems and R&D fuel cell leader, says that based on extensive analysis and modelling, Ricardo has opted to use a single balance of plant for multiple fuel cell stacks. As that equipment requires electricity generated by the cells to operate, a single system is more energy efficient. It also takes up less space and is lighter than multiple systems.
Keeping weight down is crucial: Rob Marsh, head of engineering at CAeS, points out that the fuel cells and their associated systems, plus the electric motors, are heavier than the conventional piston or turbine engines they are destined to replace.
Michael Tomlin, Ricardo senior thermal systems engineer, says that for aerospace applications another consideration is that when operating at altitude, the external air supplied to the fuel cell system is at a lower pressure than is usual for terrestrial applications. Therefore a larger compressor is needed, potentially increasing weight and power consumption. “It is definitely a challenge,” he says.
Careful selection of the individual components was required in order to “tailor the solution to the application”, he says.
CAeS intends to offer the system developed under Project Fresson to operators of the over 400 Islanders in service via a supplemental type certificate. Britten-Norman is also likely to introduce a new-build option, the airframer has indicated.
Marsh says that modelling of the likely acquisition, conversion and operating costs of a fuel cell-powered Islander “comes out cheaper” than one with a conventional engine: “It is a positive business case for future adopters of this system.”
