Transient analysis and optimization of thermoelectric generators for waste heat recovery from automotive engine exhaust

The overall efficiency of automobiles can be enhanced by recovering some of the waste heat from the engine, where more than 30 percent is lost from exhaust. Thermoelectric generators (TEGs) have gained a lot of popularity for this purpose because of their reliability and scalability. In this study, a 3-dimensional model of a TEG assembly was built, and its performance was simulated using computational fluid dynamics (CFD). The focus has been on carrying out the simulations in transient mode. Experimentally measured exhaust data from a vehicle running on a standard Indian drive cycle has been used as the boundary condition for the simulations. The TEG assembly was designed to make use of the flowing air onto the radiator to cool the cold side of the TEG. Initially, the model was validated under pseudo-transient conditions using experimental tests carried out under engine operating conditions. The effect of transience on the performance was evaluated and compared to the results based on steady-state simulations. Later, various geometric parameters of the TEG assembly were varied to optimize the overall performance of the assembly. The results showed that the steady state analysis under-predicts the performance of the TEG assembly. The optimization studies established a method to design the TEG assembly to maximize waste heat recovery without creating excessive back pressure on the engine. The results have shown that up to 355 kJ of energy with an overall efficiency of 9.9% can be recovered from the exhaust heat.