Analysis of the effects of different types of loads on a Thermo-Acoustic Engine

A Score-Stove ™ (www.score.uk.com) using a dual regenerator propane fuelled thermo-acoustic engine has been built and tested using an off-the-shelf B&C 6PS38 loudspeaker acting as a linear alternator. The configuration of regenerator comprising 30 layers of stainless steel wire was tested. Performance of the stove with resistive and diode bridge loads are compared to evaluate how nonlinear loads affect thermo-acoustic performance. The detailed construction and design issue of the tested prototype is presented. The engine pressure and the temperature profile of the Hot heat exchanger (HHX), Ambient heat exchanger (AHX), water outlet (Twout) and water inlet (Twin) have been measured and analysed to see the variation of the peak pressure and onset temperature of oscillation. Several Experiments have been carried out using different length feed back pipe with different sizes tuning stub in order to match the engine frequency with the Alternator to achieve the high electrical output. Electrical load on the linear alternator was simulated with a load box that can present a resistive, diode bridge plus capacitor, or diode bridge plus lead acid battery. Variations of pressure and temperature of the engine as well as electrical power were measured. Since the ultimate goal is to supply the power to the 12 V lead acid battery and it is necessary to match the acoustic impedance with the battery rectifier circuit to achieve the maximum output power. This paper will show that the engine with the bridge rectifier load acted the same as a resistive load that absorbed the same power. Neither of the non-linear loads had any measureable effect on conversion efficiency.