Evaluating thermoelectric modules in diesel exhaust systems: potential under urban and extra-urban driving conditions

In light-duty internal combustion engines, approximately only the third part of the fuel energy consumed is converted to effective mechanical work. Since waste energy through the exhaust system represents also around a third part of this energy input, it strikes as a remarkable source for energy recovery to reduce fuel consumption and pollutant emissions in automotive engines. Test-bench engine experiments were performed to have accurate data of exhaust gas in the most used part of the engine map in passenger diesel vehicles. To assess the potential of exhaust gases for thermoelectric modules, a simple but robust methodology has been developed. Heat transferred was calculated through fundamental equations applied to a concentric tube heat exchanger. Exergy analysis is presented in conjunction with a study of electrical power that could be produced by commercially available Bi2Te3 thermoelectric modules. These results are obtained using the exhaust system and engine coolant as they can be found in a current car, so they can be used as starting point in design of devices for harvesting exhaust waste energy, improving automotive engines sustainability. Thermoelectric generators recovery limits were made visible without focusing in a specific design.