Critical temperature ratio needed for a spontaneous gas oscillation in a miniature thermoacoustic engine

A thermoacoustic engine consists of a resonance tube and a stack that is composed of many narrow tubes; the stack is located inside the resonator. When the ratio of the temperatures at two ends of the stack exceeds a critical value, a gas in the resonance tube spontaneously oscillates and the thermoacoustic engine works. Recently, a miniaturization of thermoacoustic engines has attracted much attention due to its simplicity and high-efficiency potential. In this study, the stability limit of the spontaneous gas oscillation in a miniature thermoacoustic engine is numerically calculated by using the thermoacoustic theory. In this calculation, the stack length is taken as one of parameters. This is because when one designs a miniature thermoacoustic engine, one wants to make a stack length as long as possible to reduce thermal conduction loss along the stack. As a result of the calculation, it was fond that the length ratio largely affects the critical temperature ratio needed for causing the spontaneous gas oscillation.