A new method of flame temperature measurement utilizing the acoustic emissions from laser-induced plasmas

The optical emissions from laser-induced plasmas have been successfully exploited for elemental composition measurements in flames; however, the information from the accompanying plasma-generated acoustic emissions has not been well utilized. In this study, we investigated the influence of flame temperature and composition on the acoustic emissions from laser-induced plasmas in an ethylene-air premixed flame. The acoustic emissions are sensitive to temperature, and a negative correlation can be established. The effect of composition on acoustic emissions was found to be second order compared to that of temperature. Based on these findings, we introduce acoustic-based laser-induced breakdown thermometry (LIBT). A statistical analysis was performed to mitigate the bias introduced by anomalous extreme values. The spatial and temporal resolution of LIBT were also analyzed to demonstrate its potential to perform simultaneous composition and temperature measurements when used along with laser induced breakdown spectroscopy (LIBS). Finally, the temperature distribution in an ethylene-air counter-flow diffusion flame was measured; and the results compared favorably with numerical results.