Uncrewed Systems Technology 046

82 “We have a proprietary hydrogen recapture method that does not require a pump,” Robinson says. “We route purged hydrogen through some valves and ballasts that allow us to achieve a 99.6% hydrogen utilisation rate with no parasitic loss.” For air intake, a proprietary blower designed in-house is used, since as far as the team knows, no blower exists that is light enough to be used on a UAV while still providing enough air pressure and throughput to run the closed-cathode fuel cell. It is designed into the fuel cell system enclosure, and features an integral filter for preventing contaminants entering the oxidant feed. “An open-cathode stack just uses a fan to pull air through the cooling and oxidant paths simultaneously, but we need to force it through flow fields in the plates of the stack, so we need more pressure, hence the need for the blower,” Robinson explains. “We are also doing r&d with newer things such as Honeywell’s turbocompressors, which we think are going to bring really interesting, potentially more powerful capabilities in future generations of the fuel cell. “The blower is naturally the most energy-parasitic component on board – it represents more than 60% of the total parasitic load – but reducing the parasitic power relative to the airflow and pressure is a consistent focal point of our research. And of course, with UUVs such as Cellula’s, the oxygen comes from a tank, so in situations like those the very minor concern of the blower is replaced by more of a metering concern, as with the hydrogen.” Electrics and electronics The fuel cell controller is a microcontroller engineered in-house and based around an STM32 processor from STMicroelectronics, which is highly centralised to minimise weight and complexity. It actively manages all the BoP’s components and hence the various functions that are key to the PEMFC’s operations – including purging, current pulsing and managing the cell-by-cell voltages – by October/November 2022 | Uncrewed Systems Technology Dossier | Honeywell 600U, 600U-HV and 1200U fuel cells Honeywell selects hydrogen tank pressures based on availability – 350 bar tanks in Europe and 414 bar tanks in the US, using a pressure regulator rated up to 414 bar The fuel cells’ microcontroller is an STM32 processor. This manages purging, current pulsing, cell voltages and other functions We are doing r&d which we think is going to bring potentially more powerful capabilities in future generations of the fuel cell