Quantitative Imaging of Temperature and OH Concentration From Single Wavelength Planar Laser-Induced Fluorescence

A planar laser-induced fluorescence (PLIF) of a single wavelength is introduced to image temperature and concentration distribution inside flames. Laser absorption spectroscopy (LAS) tomography was used to provide initial images of gas temperature for image iteration. The images of temperature and concentration are used to update the fluorescence image. The fluorescence images are also corrected to update images of temperature and radical concentrations iteratively. The intensity attenuation losses due to absorption in PLIF is corrected in the iterations. Single wavelength PLIF and LAS tomography are simultaneously performed, and fluorescence image at a single wavelength is required only for each quantitative measurement. The proposed method has a twice higher speed than the classical dual wavelength PLIF. In numerical simulations, the relative error of reconstructed images of temperature is within 7% and that of the concentration is less than 3% with a signal-to-noise ratio (SNR) higher than 30 dB. Experiments were conducted on a McKenna burner, quantitative images of temperature and OH concentration were obtained and compared with computational fluid dynamics (CFDs), thermocouple, and two-color PLIF. The absolute errors are less than 30 K in the center of the burner. The relative errors of concentration are less than 7% in the flat flames.

Automated summary

This study introduces a planar laser-induced fluorescence (PLIF) technique that can be used to image the temperature and concentration distribution inside flames. The proposed method utilizes laser absorption spectroscopy (LAS) tomography to provide initial images of gas temperature, which are then used to update the fluorescence image iteratively. The results of numerical simulations and experiments demonstrate the effectiveness of this method, with relative errors of temperature and concentration within acceptable ranges.