Efficiency of the Thermoacoustic Engine Induced by Stack Position, Pipe Aspect Ratio and Working Fluid

This study investigates the performance of thermoacoustic engines by examining the influence of stack position, resonator length, and working fluid on energy conversion efficiency. Numerical simulations reveal that placing the stack at an intermediate location (e.g., 60 mm in a 350 mm resonator) maximises efficiency by promoting stable, single-mode harmonic oscillations and minimising boundary layer interference. Deviations from this optimal position (e.g., 30 mm or 90 mm) induce secondary harmonics, reducing efficiency. Doubling the resonator length while maintaining proportional stack scaling preserves performance, indicating aspect ratio is not a limiting factor. Simulations with helium, as opposed to air, yield a tripled resonance frequency (∼700 Hz vs. 245 Hz) and significantly higher efficiency (∼0.38 vs. ∼0.13), due to helium’s superior thermal and acoustic properties. These results provide quantitative guidelines for optimising thermoacoustic engine design for sustainable energy applications.