Two-stage thermoacoustic electricity generator with push-pull linear alternator

This study focuses on the design, construction and experimental evaluation of a thermoacoustic electricity generator prototype with a push-pull linear alternator. The push-pull coupling offers a solution to run the looped-tube thermoacoustic engine at high acoustic impedance using one alternator. The novel configuration of the engine consists of two identical half-wavelength stages with an alternator connected between them. A simulation was carried out using the DeltaEC programme. The modelling started by investigating the required acoustic field for the alternator. The engine modelling has been done as half of the engine which is one-stage, because the DeltaEC shooting method showed that it was unable to run two identical stages. The engine is 16.02 m long and run at 55.1 Hz. The simulation showed that it is possible to produce more than 133 W of electricity at a thermal-to-electric efficiency of 23% while using helium pressurized at 28 bar. In practice, the engine failed to self-start. After exciting it to run by an external pulse, an electric power of 48.6 W was generated with a thermal-to-electric efficiency of 2.7%. The high heat leak detected was reduced by installing an insulating gasket between the ambient heat exchanger and regenerator holder, which encouraged the electricity generation to increase. The engine became self-starting when the regenerator thickness was reduced from 73 mm to 71.8 mm. The maximum generated electric power was 73.3 W at 3.33% thermal-to-electric efficiency at a heating power of 2200 W, and a maximum efficiency of 3.6% was achieved at 71.9 W electric power at a heating power of 2000 W. The success of the two-stage engine with a push-pull linear alternator encouraged modelling and design of a four-stage engine with two push-pull linear alternators able to generate up to 269 W of electricity, theoretically.