Thermoelectric Power Generation by Harvesting the Waste Heat From a Car Engine

Abstract

Internal combustion (IC) engines typically have an efficiency of less than 35%. This is largely due to the fact that much of the energy dissipates into waste heat. However, the waste heat may be converted into electricity by using energy conversion modules made from bismuth telluride. In this work, it is demonstrated that electricity can be generated from waste heat due to the difference in temperatures. The thermal to electrical energy conversion is achieved by using a self-assembled thermoelectric generator (TEG). The TEG (thermoelectric generator) uses two different types of metallic compound semiconductors, known as n-typed and p-typed, to create voltage when the junctions are held at different temperatures. The work mechanism is based on the Seebeck effect. In this study, the TEGs are made from bismuth telluride (Bi-Te) with relatively high energy conversion efficiencies. In addition, it is readily available. The installation location of the TEG is studied. For testing purposes and convenience, the top of the radiator of a 1990 Mazda Miata car was chosen. The TEG and an aluminum finned heat sink were placed in order on the top of the radiator. Thermal paste was applied to both surfaces and secured with zip ties. A vent was cut on the hood of the car to promote airflow between the fins. Appropriate electrical wiring allowed the unit to output to a digital multi-meter which was located within the car for operator to take data. It is found from the measured results that 0.948 V is the maximum output and the average voltage is 0.751 V. The highest voltage came from driving mountain paths due to the heat sink and coolant temperature being higher than nominal. We estimate that placing an insulator between the heat sink and TEG would push the maximum voltage over 1.0 V. During the cool down phase, the TEG produced electricity continuously with a maximum voltage of 0.9 V right after engine cutoff. The voltage decreased to about 0.6 V within 40 minutes. It is found that the relationship between the temperature difference and output voltage is linear.