Yamaha and Sumitomo demo on-board thermoelectric generator for CO2 reduction

Yamaha Corporation and Sumitomo Corporation Power & Mobility Co., Ltd., a Sumitomo Corporation Group company, jointly demonstrated a new waste heat recovery system based on a thermoelectric generator (TEG), which generates electrical power via exhaust gas heat.

The TEG, which is installed in a part of vehicle exhaust system, can reduce CO₂ emissions by reducing alternator load by generating electrical power from unutilized waste exhaust gas and also by early warm-up of engine by heated coolant through the TEG unit at engine start.

In this demonstration test TEG unit was installed in a test vehicle, and the generated electrical power from the TEG and CO₂ emissions were measured with the vehicle on a chassis dynamometer. With the TEG, 1.9% of CO₂ emissions (i.e. 3.9 g/km) was reduced throughout the European WLTP driving cycle. The companies estimate the potential benefit of the TEG to be up to 3.1% CO₂ reduction (i.e. 6.4g/km) via further optimization of the vehicle installation of the TEG unit. (More on this below.)

The automotive industry has undertaken various development efforts over the years to create thermoelectric technology to reduce CO₂ emissions. However, due to the insufficient performance and reliability of the TEG module, the technology has yet to be put into practical use.

In March 2021, both companies commenced sample sales of a TEG module, YGPX024 (picture below), to investigate market needs.

The demonstration test was outsourced to FEV Europe GmbH. The test TEG unit consisted of four YGPX024 TEG modules, two heat exchangers for exhaust gas and three heat exchangers for water cooling circuit stacked together (above).

The TEG unit was installed in the exhaust pipe at the downstream of the catalyst. The main engine cooling circuit was branched and extended to TEG unit. The existing water pump on the vehicle was used to supply coolant to TEG unit. In parallel with the existing alternator the TEG unit was connected directly to an existing 12V battery via a DC-DC convertor with maximum power point tracking function, which enabled the unit to operate at its optimum and efficiently obtain electrical power. No external equipment was used for this test, due to the importance of evaluating the actual benefit for the vehicle.

The test used different test cycles, including European WLTP driving cycle (incl. Phase 4), US06 driving cycle and steady-state driving cycle. During the tests on a chassis dynamometer, CO₂ emissions and the electrical output generated from TEG unit were measured to evaluate the effect of TEG unit.

There were notable installation restrictions for the TEG unit, and the gas temperature at the exhaust inlet pipe could not reach the target value. An additional test achieved the target gas temperature. Based on the test result, analysis showed a maximum CO₂ emissions reduction of 3.1% (6.4 g/km) by optimizing the vehicle installation of TEG unit.