Investigation On Output Characteristics Of A Thermoacoustic Engine

A thermoacoustic engine(TE) converts thermal energy into acoustic power by thermoacoustic effect. Wide attention has been focused on thermoacoustic engine for its potentially high efficiency, simple configuration, reliability and environmentally friendly working gas.The history and development of TE are reviewed, followed by a brief introduction of thermoaoustic theory. Further study is made about the acoustic amplifier and the output characteristic of TE with double loads.Acoustic amplifier is a simple device which can significantly improve output pressure amplitude and pressure ratio of TE. However, the main problem of acoustic amplifier is the large acoustic power loss. Based on theoretical study, we propose a modified acoustic amplifier with larger diameter capable of further improving the performance of TE. It is shown that the modified amplifier can increase the output pressure ratio, and not significantly decrease the pressure ratio in the engine. Based on the acoustic power measurement with variable-load method, the experiments verified that the modified acoustic amplifier can decrease acoustic power loss effectively. The concept of two-stage acoustic amplifier is also proposed. In experiments, a two-stage acoustic amplifier amplifies the pressure ratio from 1.177 to 1.619 with nitrogen of 2.20 MPa as working gas, which is the highest pressure ratio obtained to date. The performance of two-stage acoustic amplifier depends on good match between the load impedance and the two-stage acoustic amplifier.In order to further improve the performance of acoustic power output and make full use of acoustic energy of TE, experiment study on double-output method is made. With working pressure and maximum pressure ratio in the torus of 2.4MPa and 1.20 respectively, investigation on acoustic power output from the torus and resonator simultaneously is carried out when nitrogen gas is used. The maximum output power, thermal efficiency and exergy efficiency reach 364.25W, 11.2% and 16.02%, which increase by 52.2%, 33.3% and 22.57% respectively than those using only one R-C load in the torus. With helium of 2.2MPa as working gas and heating temperature of 660℃, the maximum thermal efficiency reaches 11.14% with double-output method, which increases by 38.56% than that with single-output method.