Unmanned Systems Technology Dec/Jan 2020 | Phoenix UAS | Sonar focus | Construction insight | InterGeo 2019 | Supacat ATMP | Adelan fuel cell | Oregon tour | DSEI 2019 | Copperstone Helix | Power management focus

68 December/January 2020 | Unmanned Systems Technology metal bulkheads for structural strength, protection, and the recovery and balance of heat. However, the company replaces the metals with carbon fibre, which cuts the weight of the base 100 W system from 5 kg to 1.5 kg, for applications where lightness is important. “Insulation is key to SOFC efficiency – the more heat you lose, the more you need to generate in order to keep that 700-750 C operating environment,” Dr Kendall explains. “The first process during start-up is the temperature increase via an electrical heater, with later exothermic reactions in the cells. “By recycling the heat and keeping it all inside the cell chest, after the start-up period your net energy increases and the heat management takes over to build and maintain temperature. And the air intake increases when needed to prevent too much heat building up.” Thus the first stage in the operation of the mSOFC module comes from the gas management system, which introduces the fuel into the module. The fuel tank can feed the gas through a pressure regulator, but an unadjusted fuel canister pressure has worked well enough. The fuel then passes through a flow control valve on the inlet of the fuel cell module, which can be closed if and when the fuel supply has to be cut off. Between the inlet valve and the cell stack, a CPOx reactor is used to partially combust the fuel, thus extracting hydrogen from it and also providing heat. Steam reforming and auto-thermal reforming can be more energy-efficient but they need an additional water tank, which would substantially increase the volume and weight of the module. The hydrogen and heat output by the CPOx unit flows into an initial chamber, where the rubber tubes attached to the input ends of the fuel cells are fitted. The gas fills the chamber evenly across the rubber inlets, and flows into the cells. An elongated recuperator parallel to the fuel cells provides for the collection and reuse of heated exhaust gases to help build the heat up towards the targeted 700-750 C. The intake of air for providing both oxygen and cooling is managed by fans blowing the air onto the fuel cells from above, mainly onto the middle of the cells, the primary area of thermal concern. Temperature sensors in the module detect when the internal environment rises above 850 C, and the fans’ speed increases to compensate. Being metallised, the ceramic has wires attached to create a circuit interconnecting the cells, which then connect to the hybrid battery. No balancing of the fuel cells is required as the DC power is supplied directly to the battery. “We could also put in sensors for detecting oxygen, pressure levels and gas flows, but they’ve proved unnecessary to our operations so far – the more sensors you pack in, the more expensive the system becomes,” Dr Kendall remarks. The efficiency of the system – in terms Dossier | Adelan solid oxide fuel cell Base fuel cell Cell length: 15 cm Cell diameter: 1 cm Cell weight: 13.5 g Maximum power output: 10 W Anode material: nickel oxide Electrolyte: yttria-stabilised zirconia Cathode: lanthanum strontium cobalt ferrite Fuel cell module (cell stack and balance of plant) Fuel types: Includes gasoline, diesel, heavy fuels and propane biofuels Cooling: air Dimensions: 220 x 550 x 175 mm Weight: 1.5 or 5 kg Operating power: 100 W Peak power: 200 W Operating voltage: 12 V Operating current: 0-10 A Lifetime: more than 3000 h Some key suppliers Ceramics: undisclosed Flow control valve: Huizhou Yingye Motor Co Cooling fans: Sunon Heater: Technologic UK Recuperator: undisclosed Rubber tubing: RS Components ECU: in-house Temperature sensors: TC Direct Electrical connectors: RS Components Wiring and wire harnesses: undisclosed Seals: RS Components Fibreglass: RDM Insulation: Morgan Structural metal parts: undisclosed Fasteners: undisclosed Specifications Diagram of the cell stack and balance of plant