Basic research thermogenerator - analysis and system integration of high-temperature materials in motor vehicles

Project name

Basic research thermogenerator - analysis and system integration of high-temperature materials in motor vehicles

Project duration

01.02.2011 - 31.07.2013

Brief description

As part of the research project, a multi-stage procedure for the integration of high-temperature thermoelectrics in the exhaust tract of combustion engines was proposed and implemented. While the focus in the first project period was on the general definition of the boundary conditions, the basic descriptions of the interfaces and the actual integration options, the second part of the project was concerned with the concretization and implementation of individual measures.
At the beginning, a basic analysis of different module shapes and module designs was carried out with the help of constructive development processes and CFD simulations. In particular, the encapsulation of the thermoelectrics was considered to have great potential, as this would result in numerous simplifications in the design of the overall system (e.g. bracing). However, the disadvantages of this solution are the heat transfer between the cold and hot sides via the capsule itself, which results in a reduction in efficiency, and the complex production of the modules.
Following these investigations, two heat exchanger concepts, which were already presented in the first reporting period, were examined in detail. One was a conventional system with the modules braced between the cold and hot sides and the other was an octagonal heat exchanger, which would have required module encapsulation. Both concepts could be represented virtually with all design and manufacturing details and then examined for their thermal and fluidic properties using CFD programs. Due to the high level of complexity and, above all, the lack of encapsulated high-temperature modules, the initially promising octagonal concept could not be implemented. Instead, the conventional demonstrator was used for production, which was successfully implemented by the end of the project. The focus here was on a high degree of modularity for measuring different modules (size, operating temperature) and heat exchangers (hot side), as well as on the precise energy balance of the system. Furthermore, variable use on hot gas and engine test benches was planned, which was also successfully implemented. For reasons of time, and above all due to the lack of new modules, the finished demonstrator was not initially set up on the test benches, as the effort involved would have been considerable. Instead, an alternative system with low-temperature modules was installed and measured on the highly dynamic engine test bench prior to production. The experience gained was initially incorporated into the design and manufacture of a separate demonstrator. The control structures and control systems set up on the test bench will also be used again when the heat exchanger system is set up at the end of the project.
By the end of the project, a great deal of information and recommendations regarding the integration of thermoelectric generators in combustion engines had already been provided. A heat exchanger was manufactured that enables the measurement and evaluation of various modules and heat exchanger structures. The preceding extensive CFD analyses have deepened the understanding of the processes in thermoelectric systems and made them usable for later projects.
By creating the possibilities for thermal balancing on the hot and cold side and electrical analysis on the test bench, detailed statements can be made in future about the effectiveness of thermoelectric generators in the exhaust system of combustion engines.

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