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Designing regenerators of thermoacoustic engines for automotive waste heat recovery
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 14, 2020 by SAE International in United States
Abstract: Extraction and utilization of automotive waste exhaust heat is an effective way to save fuel and protect the environment. One promising technology for this purpose is the thermoacoustic engine, where thermal energy is converted to mechanical energy in terms of high amplitude oscillations. The core component in a thermoacoustic engine is a regenerator where the process of energy conversion is mainly realized. This paper introduces a strategy for the design and optimization of this regenerator. It is then applied to typical light- and heavy-duty vehicles. Starting from 1-D linear thermoacoustic theory, the nonlinear effects (given by the high amplitude oscillations) are modelled as acoustic resistances and introduced into the basic linear equations to estimate the nonlinear dissipations in the regenerator. Then, a few dimensionless parameters are derived by normalizing these thermoacoustic equations. This yields a good overview of how different design parameters such as the geometrical dimensions, operating frequency, and thermal boundary conditions influence the performance of the regenerator. The results obtained in the current work show that the optimum designs for the regenerators in thermoacoustic engines aimed at light- and heavy-duty applications widely differ due to the different thermal properties of their exhaust gas. Even for the same application, the optimum design for the regenerator varies with the practical objective, i.e. the maximum generation of acoustic power or maximum thermal efficiency. Finally, two actual designs of the regenerators in thermoacoustic engines for the typical light- and heavy-duty applications are carried out.