Researchers from the Berner Fachhochschule and EMPA, a Swiss research and services group, are developing a thermoelectric generator for vehicle waste heat recovery that is integrated in the muffler, rather than being installed as a separate thermoelectric generator (TEG) unit on the exhaust line.
|Prototype for the integrated thermoelectric system. Click to enlarge.|
They presented their work at the 2010 Spring Meeting of the Materials Research Society (MRS), held in San Francisco all this week.
The thermoelectric system was developed after a study of existing systems and project-relevant theories as well as different tests to evaluate the potential of waste heat recovery. The team used models to describe the operational behavior of the generator under simplified conditions, with a special focus on the electrical power generation dependence on the exhaust mass flow and the exhaust gas temperature.
One advantage of their design, the researchers say, is that flow resistance of an integrated generator is kept low without any additional parts; by contrast, a discrete TEG mounted on the exhaust line can require a complex bypass system that prevents backpressure caused by heat exchanger elements to rise over unacceptable values.
To avoid overheating without the use of a bypass system to help regulate the temperature, the TE device uses a mechanism employing bimetallic strips that disengages the modules of the heat source when reaching maximum operating temperature.
To verify the theoretical values and to understand the behavior of such a recovery system, they built and tested a prototype based on the muffler of a VW Touran. Based on initial results, they believe the system can be optimized and result in a twenty-leg oxide thermoelectric module integrated into the muffler.
With further improvement and higher conversion efficiencies, the recovered energy will be high enough to meet the electrical requirements of a car and thus improve fuel efficiency by up to 5%.
MRS 2010 Spring, DD2.6: Thermoelectric System for Waste Heat Recovery in Cars. M. Trottmann et al.