Study of Dynamic Behaviors of Thermoacoustic Oscillations by Using Laser Absorption Spectroscopy

The present work demonstrates the feasibility of dynamic characterization of thermoacoustic oscillations using temperature-based method. Experiment was conducted in a typical thermoacoustic system using a line-of-sight laser absorption measurement system. The unexpected laser beam steering and water vapor condensation encountered in the experiment were eliminated via adopting the optical integrating sphere and gas heating device, respectively. The measured temperature signals were compared and validated by the synchronous pressure signals obtained by a pressure transducer. Comparison results indicate that the dominant characteristic contained in temperature and pressure signals are consistent, but the temperature signals catch more detailed information than the pressure signals. To further extract transient features from the temperature signals, the multi-cycle average-based method and the time-frequency analysis based on the Hilbert-Huang transform were then conducted. The underlying mechanism responsible for the temperature characteristics were analyzed based on the multi-cycle averaged signals and HHT spectrum. Results show that the proposed temperature measurement method is effective in characterizing the transient temperature in the thermoacoustic oscillations. The temperature oscillations catch abundant information (e.g., obvious second harmonic component), which can provide comprehensive reference data for in-depth understanding of mechanism of the thermoacoustic oscillations.