The performance improvement of a cascade thermoacoustic engine by adjusting the acoustic impedance in the regenerator

A novel cascade configuration consisting of one standing wave unit and one travelling wave unit arranged in series is studied in this paper. Theoretically, a straight-line cascade engine provides an efficient energy conversion, reduces the difficulties of fabrication and allows no Gedeon streaming. In order to achieve such a powerful cascade thermoacoustic engine, the regenerator of the travelling wave unit must be operated in high impedance and travelling wave phasing region. Various techniques of phase adjustment by modifying the configurations and geometrical dimensions of the system are investigated both numerically and experimentally in order to adjust the position of the sweet spot as well as to promote the acoustic impedance in the regenerator. It is found that the effective tuning methods with less modification here are accomplished by changing the volume of down-cavity and reducing the flow area of down-resonator by inserting the pencil. The exploration also shows that the acoustic field in the system is quite sensitive to the effect of down-resonator length. The performance of the proposed system is clearly improved after the phase-adjustment schemes are completely implemented, in which the regenerator works within the sweep spot zone with high acoustic impedance. Copyright (c) 2016 John Wiley & Sons, Ltd.