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In a thermoacoustic engine, acoustic impedance plays a key role to improve the system performance. A matching stub is a component which can be applied to adjust the acoustic impedance. In this study, the effect of locations and lengths of the stub was investigated. The travelling wave engine was designed in looped-tube configuration operating at the frequency about 65 Hz. Air was applied as a working medium, operating at atmospheric pressure. The simulations and experiments were carried out to validate the function of the stub. With a variation of the stub length and its position along the looped-tube, the acoustic impedance can be fine-tuned to obtain the travelling wave phasing in the thermoacoustic core and maximum generated acoustic power.

Graphical abstract Highlights • Looped-tube engine with a single stage numerically designed. • Different methods of acoustic matching applied. • Phase and impedance adjusted by position and volume of effective elements. • Configurations with stub, compliant and inertial segment compared. • Performance in dependency of segment length discussed. Abstract Looped-tube thermoacoustic engines have shown to be operational with low temperatures. When equipped with multiple stages, preferable acoustic conditions are inherently achieved, leading to high efficiency. However, engines with only a single stage are able to achieve a similar performance, when acoustic disturbances are properly matched by implementation of an additional, acoustically effective element. Furthermore, acoustic conditions in the regenerator can be accurately tuned by adjusting the element's volume (i. e. impedance) and position in respect to the regenerator. The present work compares three different methods for acoustic field adjustment: a side-branched stub, a compliant segment and an inertial segment. The last two are widened or narrowed sections of the feedback loop, respectively. The influence of different general positions is considered. All configurations are analysed and compared with each other regarding their acoustic tuning capabilities and possible side effects to the acoustic field. As a result, superior engine performance is achieved by use of a compliant segment, closely followed by use of a stub. Furthermore, the length of a compliant or inertial segment has a major impact on performance. While extending a compliant segment slightly improves power, it can be crucial for an inertial segment. The comprehensive analysis is carried out numerically under identical conditions for each configuration. DeltaEC (Design Environment for Low-amplitude Thermoacoustic Energy Conversion) is used as simulation software. [ABSTRACT FROM AUTHOR]