Simultaneous Quantitative Imaging of Temperature and H₂O/CH₂O Concentration by Using LAS-Fused Nd-YAG Laser-Induced Fluorescence

A planar laser-induced fluorescence (PLIF) using the third harmonic of the neodymium-doped yttrium aluminum garnet (Nd-YAG) laser at 355 nm is employed to visualize temperature and H2O/CH2O concentration distributions inside flames. Laser absorption spectroscopy (LAS) is employed for initial images of temperature and H2O concentration, and the measured absorption offers constraints to update temperature and H2O concentration images. A chemical reaction kinetics model based on ethanol combustion mechanisms is established, offering the production rate of H2O and CH2O, thereby bridging PLIF and LAS. The images of temperature and CH2O/H2O concentration are produced iteratively for quantitative imaging of the flame cross-section. A flame fueled with ethanol vapor was used, and the images of temperature, H2O concentration, and CH2O concentration were given. Compared with thermocouples, the temperature difference was found to be no more than 40 K. The images of H2O and CH2O concentrations detailed the area of incomplete combustion within the flame and its temporal variations. Relative deviations from the experiment results to the ideal values are, respectively, 3.05% and 5.34% for H2O and CH2O.