Semi-Analytical Determination of the Onset Conditions of Thermoacoustic Engines

Several analytical or numerical models available in the litterature allow to predict the onset of thermoacoustic engines [5, 6, 11]. However, most of these models rely on strong assumptions concerning for instance the stack geometry or the shape of the temperature field in the thermoacoustic core. The purpose of the work presented here is to put forward a new method allowing the prediction of the onset of the thermoacoustic instability while being exempted from a certain number of these assumptions. This method consists in measuring the transfer matrix of the thermoacoustic core by means of an appropriate experimental setup developed in our laboratory. The results are then introduced into an analytical modeling leading to the prediction of the onset conditions (in terms of heating power supply and acoustic frequency) of the thermoacoustic instability in an engine of specified geometry (straight duct or closed loop, coupled or not with an acoustic load like a secondary resonator or an electrodynamic alternator). The results of measurements will be presented, and the predictions of the onset obtained from these measurements will be compared with those actually observed in a standing-wave thermoacoustic engine.