Thermoacoustic Cascade Engine Free from Resonance Length

The high reliability and long lifespan of thermoacoustic generators (TAG) make them ideal for waste heat recovery applications. However, the size and weight of these generators is still a challenge. This paper introduces a traveling-wave thermoacoustic generator that is free from a wavelength long loop. The new generator consists of an acoustic driver (linear motor), thermoacoustic engine and a linear alternator. The linear motor introduces the initial acoustic power into the thermoacoustic engine which amplifies it, then the amplified acoustic power is converted into electricity through the linear alternator. The electric power obtained from the alternator exceeds the initial input (“seed”) power consumed by the motor to kick-start the thermoacoustic amplification, thus providing the net power gain. The advantage lies in decoupling the operation from the reliance of the acoustic resonance. A two-stage engine can be built with half a meter length, while a three-stage engine can be less than a meter long including a coiled inertance pipe. The three-stage TAG can generate 120.5 W of electricity, at a thermal to acoustic efficiency of 34.2% and a total efficiency of 20.5%.