Entwicklung eines Direkt-Methanol-Brennstoffzellensystems der Leistungsklasse kleiner 5 kW

The attractiveness of electrical conversion of liquid methanol in a fuel cell is defined by its simple storage and high energy density. Therefore, direct methanol fuel cell (DMFC) qualifies for applications in portable systems and mobile application in the kW-class. The goal of this work is to develop and demonstrate an improved and optimized peripheral DMFC system compared to the current level of technology. The selected mobile application is the retrofit of the energy supply of a "Scooter" with a fuel cell system. The required size reduction and the simplification of the DMFC system are realized by an integrated concept, which combines ideally the peripheral system and the fuel cell. A profound analysis of the stack and the peripheral components is a prerequisite for an optimized design. A detailed modelling and understanding of the stack behaviour establish the starting point of this work. The influence of the most important operating parameters like stack temperature, cell voltage, current density, air ratio and methanol concentration is captured accurately by the developed model and validated by experimental data. This shapes the frame work of the following system design approach. For this the clearly defined task of the peripheral system are investigated individually for alternatives and the best option is selected for the final solution. For selecting the right pumps and blowers available products and prototypes are characterized and checked for the system requirements. The investigation and the modelling of the exhaust gas condenser lead to an optimized component design for the “Scooter” DMFC design. Additionally, the integration of the anode loop is accomplished consisting of the supply lines, the circulating pump, the gas separator and the exhaust line. The direct coupling of the fuel cell with a lithium-ion battery as an option for electrical conditioning is investigated. In the system modelling the influence of the operational parameter on characteristic performance indicators like electrical power, efficiency, and power density is analysed in combination with the heat and water management of the system. The system can be optimized only for single specific targets. For example the best system efficiency has been evaluated for a cell voltage of 400 mV and a stack temperature of 70°C. In the final part the development of the power supply of a Scooter is described. A compact system witha net power output of 1230 W has been realized. The system efficiency amounts up to 18.8%.