Airbus has partnered Parker Aerospace to develop a hydrogen-based replacement system for the auxiliary power unit, which could find its first application on the projected next-generation single-aisle aircraft beyond 2020.
The agreement will add to the airframer's previous research into fuel cell technology and build a technology demonstrator to be flight-tested in 2015. The plan is to offer this to a new aircraft development team at "technology readiness level 6 (TR6)" about one year later, Axel Krein, Airbus senior vice-president research and technology, says. Unlike current APUs, the new system will not only generate electricity and, if still needed, bleed air but also portable water and oxygen-depleted air (inert gas) as by-products of the chemical reaction between hydrogen, which will come from a fuel tank, and oxygen in the ambient air.
While the water can be fed into the aircraft's freshwater system, the inert gas could be used for the fire suppression equipment in the main fuel tanks and cargo compartments, for which bottled gas is currently used. The fuel cell solution would therefore lead to a fundamental change in system architecture and rule out a retrofit option for existing models, including the forthcoming Airbus A350 and A320neo. A first application could be on the projected narrowbody successor A30X, Krein says. Airbus has progressively pushed the arrival of that generation back, currently forecasting service entry around 2030.
The challenge is to optimise the aircraft's overall architecture for the new system. The fuel cell technology should deliver a fuel burn reduction on a standard short- to medium-haul mission of 10-15%, Krein says.
However, the overall benefit would depend on how cost-effectively the hydrogen system can be introduced to aircraft and ground operations. Reducing the fuel cell system's weight and maintenance costs will be important. Weight will be helped by the reduced need to take fresh water onboard at the airport. Engineers will need to determine the amount of reduction or the possibility of producing all fresh water with the fuel cells.
Krein says while it is possible to build a fuel cell prototype at the targeted weight, this would come at a high cost and would not be feasible for serial production. He adds that competitive maintenance costs will be another challenge given the increased complexity of the new system and the fact support for conventional equipment has become virtually automated.
While Parker will supply the fuel cell system and manage different sub-system suppliers, Airbus will be responsible for the overall aircraft system architecture. Krein says the fuel cell could also be used to power electric motors to move the aircraft on the ground.
Source: Flight International
