A WMS Based TDLAS Tomographic System for Distribution Retrievals of Both Gas Concentration and Temperature in Dynamic Flames

A tunable diode laser absorption spectroscopy (TDLAS) tomographic system was proposed via utilizing the wavelength modulation spectroscopy (WMS) method and distributions of temperature and specie concentrations in the dynamic flames were simultaneously reconstructed for the first time. A five-view fan beam tomographic sensor was applied to capture the absorption spectrum along the laser paths across the region to be imaged. Light intensities in all paths were collected in a custom specific TDLAS hardware. Different phantoms of the temperature and water vapor concentration distributions were fabricated to generate artificial data of the absorption spectrum acquired in the sensor. Reconstructed images of the phantoms in the simulations agreed well with the original distributions, in cases of different random noises that varied from 1% to 7% of light intensities at each wavelength. Experiments on a McKenna burner and the exit of a wind tunnel were carried out, and distributions of temperature and water vapor's molar concentration were achieved by applying the proposed WMS based TDLAS tomographic system. A moving steel ruler was used to disturb the flame in the burner and temporal variations of the flame over a cross section of the burner were imaged in a tomographic way. Tomographic results on exhaust flows at the exit of a wind tunnel coincided with the variation trend of temperature in eleven different working conditions and verified the robustness of the proposed system under harsh conditions.