Modeling Analysis of Waste Heat Recovery via Thermo Electric Generators for Fuel Economy Improvement and CO ₂ Reduction in Small Diesel Engines 2014-01-0663

This paper deals with modeling and analysis of the integration of ThermoElectric generators (TEG) into a conventional vehicle, specifically aimed at recovering waste heat from exhaust gases. The model is based on existing and commercial thermoelectric materials, specifically Bi₂Te₃, having ZTs not exceeding 1 and efficiency below 5%, but a trade-off between cost and performance that would be acceptable for automotive applications. TEGs operate on the principle of thermoelectric energy conversion via Seebeck effect, utilizing thermal gradients to generate electric current, with exhaust gases at the hot side and coolant at the cold side. In the simulated configuration the TEG converters are interfaced with the battery/alternator supporting the operation of the vehicle, reducing the energy consumption due to electrical accessories and HVAC.

Heat exchanger models for steady-state solutions have been simulated to estimate the actual temperature of hot and cold sides, as a function of vehicle operation and TEG configuration. The TEG module model has been validated with respect to existing literature, showing agreement with published results.

The overall model - integrated into a backward longitudinal model of a FIAT Punto 1.3 Diesel - outputs recovered electric energy as function of hot side (exhaust gas) and cold side (coolant) temperature and mass flow (provided by the vehicle model). Several simulations have been carried out to explore different driving conditions and TEG configurations. Results show that for the analyzed vehicle model, TEGs can displace up to 15-20% of the alternator energy with average CO₂ savings above 1g/km on standard driving cycles.