SAE 2017-01-0153 : 2017

Nearly a third of the fuel energy is wasted through the exhaust of a vehicle. An efficient waste heat recovery process will undoubtedly lead to improved fuel efficiency and reduced greenhouse gas (GHG) emissions. Currently, there are multiple waste heat recovery technologies that are being investigated in the auto industry. One innovative waste heat recovery approach uses Thermoacoustic Converter (TAC) technology. Thermoacoustics is the field of physics related to the interaction of acoustic waves (sonic power) with heat flows. As in a heat engine, the TAC produces electric power where a temperature differential exists, which can be generated with engine exhaust (hot side) and coolant (cold side). Essentially, the TAC converts exhaust waste heat into electricity in two steps: 1) the exhaust waste heat is converted to acoustic energy (mechanical) and 2) the acoustic energy is converted to electrical energy. The converted electrical energy can be used to offload the alternator, supplying power for auxiliary loads as well as battery charging. In the event of excess electrical energy, it can be returned to the drivetrain through a motor connected to the front end accessory drive (FEAD). With the increasing demand for clean energy, TAC could be an attractive alternative for reducing fuel consumption and CO 2 emissions. Such a technology will become more attractive as electric power loads on a vehicle increase through hybridization and the increased usage of infotainment systems, media, and connected vehicles. In this paper, the fundamental principle of TAC technology is described and the TAC waste heat recovery vehicular integration with exhaust is presented. Numerical simulations are performed on light-duty gasoline pick-up truck engine exhausts over the US certification cycles to assess the performance and potential of TAC technology. Finally, some of the technical challenges are presented as well, acknowledging technology maturity and risks.

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