Development of Large Scale DMFC System for Aviation Applications

Abstract

Due to the trend of an increased electrical energy usage on board of aircraft and more restricted environment concern for reducing the pollutant and CO 2 emission, fuel cell technology becomes attractive for aviation application. Thanks to the inherent advantages of using liquid fuel and system simplicity, direct methanol fuel cells (DMFCs) present a great potential application for replacement of APU in aircraft. In present work, we will focus on finding out the optimum working conditions for the large scale DMFCs. Electrochemical impedance spectroscopy (EIS) is used as a powerful diagnostic tool for achieving the goal. It was found that humidification is necessary for obtaining the ideal fuel cell performance as working temperature is higher than 70 o C. VIATION plays a key role in the economic prosperity and is growing by 5.9% per year. However, according to the concern of the environment issues and global warming, aviation accounts for about 13% of all transportation related CO 2 emissions. In order to reduce the pollution from the ever increasing numbers of aircrafts, it is expected to reduce the aircraft fuel consumption and emissions in the future. Fuel cells provide an attractive option, which are inherently cleaner power sources and higher efficiency than auxiliary power units. Fuel cells will not replace jet engines on commercial transports, but they could replace gas turbine auxiliary power unit as the technology becoming more mature. For this application, fuel cells can be used to power non-critical loads like galleys and in-flight entertainment. Waste heat and waste water from the fuel cell can be used to improve the overall efficiency. Direct methanol fuel cells are electrochemical devices that convert chemical energy of liquid methanol directly to electricity in an environmentally friendly way for various applications. DMFC can provide electricity (and heat) continuously as long as methanol and oxygen are provided. As methanol is easy to store and transport and has a very high energy density, DMFC presents an inherent advantage on producing a lot of electric power with liquid fuel stored in a fixed volume. Since space and weight are at a premium in most aircraft, DMFC is attractive for aviation applications (1). We initialed a project for developing a complete 1 kW DMFC system with the potential to be scaled-up to tens of kW range in the following projects for replacement of the anxious power unit (APU) in aviations applications. A schematic diagram of the fuel cell system and 3-D sketch overview of the system are shown in Figure 1. The system will maintain the fuel cell stack working at constant temperature, proper methanol concentration and guarantee the water balance. Air is provided to the fuel cell stack by an air pump. Moisture in the cathode exhausting gas is captured at the condenser and the recovered water is sent to the liquid/gas separator for making up the water loss. A methanol supply pump is used to dose methanol into the liquid/gas separator to keep the methanol concentration constant. The dilute methanol solution is circulated through the stack and radiator. The waste heat produced in the stack is absorbed in the anode liquid flow and dissipated to the ambient environment at the radiator. Alternatively, this waste heat can be reused for supply of hot air or water for the galley in a commercial airplane.