Micro air vehicles (MAVs) are small remote controlled aircraft used by military personnel for reconnaissance and are currently powered by batteries. The MAVs rely on the battery for propulsion, navigation, and reconnaissance equipment. The thrust of this research is to develop a fuel cell system capable of higher power densities, higher power to weight ratios, and increased overall power output than the batteries in use today. To this end, a feasibility study is first conducted to determine if fuel cells could be used to replace batteries as the MAV power source and what fuel cell configurations would show the best performance. Hydrogen, methanol, and formic acid fuel cells are considered, using a conventional flat-plate design and a novel micro-tubular design. Several micro-tubular fuel cells (MTFCs) are tested to show that these cells are a possibility for power production in MAVs. Those tested are developed and improved in collaboration between Luna Innovations, Inc. and the Center for Energy Systems Research at Virginia Tech and then manufactured by Luna Innovations, Inc. Also, an isothermal, lumped-parameter (LP) model for MTFCs is developed to predict behavior. The use of this LP model aids in understanding the dominant losses of the cell and ways of improving cell performance. Results from the feasibility study indicate that by using methanol powered MTFCs a 50% increase in overall energy output is possible, while also decreasing the mass of the power production system. Through testing and an iterative design process, an increase of three orders of magnitude of the maximum power production of the MTFCs constructed by Luna Innovations, Inc., has been realized. Results of the LP MTFC model are compared with the experimental results from the MTFC testing and tubular cells from the literature. / Master of Science

Modern society has become reliant on battery powered electronic devices such as cell phones and laptop computers. The standard way of recharging these devices is by connecting to a reticulated electricity supply. In situations with no electricity supply some other recharging method is required. Such a possibility is a small, portable, generator based on fuel cell technology, specifically mini-tubular solid oxide fuel cells (MT-SOFC). MT-SOFCs have been developed since the 1990s but there is limited analysis, discussion or research on developing and constructing a portable generator based on MT-SOFC technology. Such a generator, running on a portable gas supply, requires combining the key aspects of cell performance, a heating and fuel reforming system, and cell manifolds. Cell design, fuel type, fuel flow rate, current-collection method and operating temperature all greatly affected MT-SOFCs performance. Segmenting the cathode significantly increased the power output. Maximum power density from an electrolyte supported MT-SOFC was 140 mW/cm2. The partial oxidation reactor (POR) developed provided the required heat to maintain the MT-SOFCs at an operating temperature suitable for generating electricity. The exhaust gas from the POR was a suitable fuel for MT-SOFCs, having sufficient carbon monoxide and hydrogen to generate electricity. Various manifold materials were evaluated including solid metal blocks and folded sheet metal. It was found that manifolds made from easily worked alumina fibre board decreased the thermal stresses and therefore the fracture rate of the MT-SOFCs. The final prototype developed comprised a partial oxidation reactor and MT-SOFCs mounted in alumina fibre board manifolds within a well-insulated enclosure, which could be run on LPG. Calculated efficiency of the final prototype was 4%. If all the carbon monoxide and hydrogen produced by the partial oxidation reactor were converted to electrical energy, efficiency would increase to 39%. Under ideal conditions, efficiency would be 78%. Efficiency of the prototype can be improved by increasing the fuel and oxygen utilisation ratios, ensuring heat from the exhaust gases is transferred to the incoming gases, and improving the methods for collecting current at both the anode and cathode.