Thermoelectric Energy
FIGURE 36-15
Thermocouple.

If two different metals are joined and heated, a small electrical current can be generated. For a temperature rise of around 392°F (200°C), the potential difference created is about 9 millivolts. The point that is heated is called a hot junction, and the whole system is called a thermocouple Figure 36-15.In developing engine designs, manufacturers use thermocouples to measure the high temperatures of components, such as spark plugs and exhaust systems. Thermocouples are also used to measure exhaust gas temperature on race cars to determine the best air–fuel ratio so that the engine parts will not be overheated. Pilots in general aviation use thermocouples to measure the exhaust gas temperature to adjust the fuel mixture as the airplane changes altitude.