Unmanned Systems Technology 022 | XOcean XO-450 l Radar systems l Space vehicles insight l Small Robot l BMPower FCPS l Prismatic HALE UAV l InterDrone 2018 show report l UpVision l Navigation systems

61 BMPower fuel cell power system | Dossier The gas diffusion layers are on top of the catalyst layers. These are made from carbon and are very porous and hydrophobic. Ivanenko says, “We use gas diffusion layers with an additional microporous layer. The purpose of that layer is to hold some water for membrane self-humidification. That layer and the doped membrane allow the system to work without a hydrogen humidifier.” In terms of the oxygen feed to the cells, he notes, “Our open-cathode technology provides the maximum simplicity [ease of use] and the minimum system weight [clearly very important for the UAV market]. “Using an open cathode, air is supplied at atmospheric pressure without any special preparation in the FCPS. In this way, we optimise the weight of the air supply system for reaction and cooling. Our fans perform both these functions at the same time and thus offer the minimum possible weight. In the near future, the comparable weight of an alternative cooling system will be more than double, given that we are developing more advanced fans.” Ivanenko notes that using air rather than liquid cooling negates the need for a coolant pump. “Our air supply system simultaneously performs the function of air cooling, an approach that slightly reduces the power of FCPS,” he says. “However, at the same time it saves a lot of weight and energy consumption by auxiliary systems such as a liquid cooling system and a hydrogen humidifier. In the end, our approach increases the specific energy density of the whole system. “Our approach means each fuel cell has straight rather than serpentine channels for the air supply, while our cooling system delivers far more volume of air for cooling compared to a more traditional approach. We believe that building up significant pressure is not justified in an open-cathode system – it implies excessive energy consumption. “In order to optimise the heat dissipation and electrical conductivity, we developed a special air channel profile, selected conductive, corrosion- resistant coatings and developed a new technology of coating. In addition, we are going to embed in our fuel cells a new type of bipolar plate, which is even more efficient.” He adds, “We do not alter the way the fan blows into the cathode depending on the power or current consumption. The intensity of the airflow reaching the cathode is determined by the need to maintain the correct operating temperature. In our system, the amount of airflow for the cathode is sufficient [with a significant excess] for the electrochemical reaction in any weather conditions. Hydrogen is automatically consumed in the necessary amount for the reaction, because we also use a ‘dead-ended’ anode.” BMPower maintains an operating temperature of around 50 C. Ivanenko explains, “The temperature affects the rate of water vaporising and thus membrane humidity. We don’t use a hydrogen humidifier to avoid the system becoming more complicated and heavier. So, we optimise the operating temperature with reference to membrane self-humidification. The fact that our approach is to use membrane self- humidification, a microporous layer in the gas diffusion layer and membrane doping allows us to avoid forced humidification of hydrogen.” The control module for the BMPower 1000 FCPS BMPower is currently working on this aircraft, which will have a maximum take- off weight of 24 kg, carry a payload of up to 3 kg and fly for three-and-a-half hours using a 1500 W FCPS substituting an ICE Unmanned Systems Technology | October/November 2018