バイオディーゼル駆動水冷ディーゼル機関における熱電素子を用いた排熱発電の検討

抄録

This paper describes a waste-heat recovery and power-generation system based on a thermo-electric module (TEM) for a water-cooled diesel engine using a carbon-neutral fuel such as biodiesel. The system integrates a heat exchanger for the engine exhaust gas, a TEM and a power-conversion circuit using maximum power point tracking control and a DC-DC converter. The power generated by the system was used to charge a 12 V lead-acid battery. The results indicated that during continuous engine operation, the TEM voltage decreased almost linearly with increasing output current. Simultaneously, as the current increased, the temperature difference between opposing surfaces of the TEM decreased due to the Peltier effect. Consequently, the maximum electric power output from the TEM during power generation was about 60 to 70% of that calculated based on the measured open-circuit voltage. Regardless of the engine operating conditions, the battery was steadily charged because the TEM output power was maintained at a maximum by the control circuit. An evaluation of the circuit performance during power generation showed that the power utilization efficiency, i.e., the ratio of the circuit input power to the maximum output power of the TEM, was around 88 %. In addition, the power conversion efficiency, i.e., the ratio of the circuit output power to the input power, was about 91%. When considering the internal resistance of the conductor wire in P_uti, these values are similar to those previously determined using a DC power supply to simulate the TEM output power.