Utilization of exhaust gas thermal energy – theoretical investigation

Even modern internal combustion engines have no more than 40% of efficiency. The remaining 60% of the energy gained from the burning fuel is considered as waste energy. Half of the waste energy is transferred to the environment by the exhaust system. As the exhaust gas has higher temperature than the environment the heat energy of the gas could be utilized. Although this idea is currently being researched by car companies to increase the fuel economy, our purpose with the present research is not to decrease the consumption but to generate electricity from the temperature difference based on the Seebeck effect. The produced electricity can power an emission reducing unit. The theoretical investigation of exhaust gas energetic utilization is described in the paper. The Seebeck efficiency of a 50 W nominal power Peltier element was determined with a measurement series. Based on the lower heating value (LHV) of diesel oil the achievable exhaust energy was calculated. A thermo picture was taken to determine the temperature gradient around the exhaust system on a real car. Finally the necessary Peltier element area was calculated.