A computational study for tomographic imaging of temperature, water and carbon dioxide concentration in combustion gases using a single tunable diode laser.

There is a present-day need of optimization of the combustion processes and catalytic efficiency for minimization of emission of pollutants, which can be possible by analyzing the temperature and combustion products distribution in the combustion processes internally. This paper discusses the feasibility of simultaneous 2-D tomographic imaging of temperature and concentrations of CO$_2$ and H$_2$O by scanning a single narrowband laser. The choice of spectroscopic lines of H$_2$O for two-tone temperature measurement is discussed around the wavelength range of 2000 nm. This region is selected as both H$_2$O and CO$_2$ spectral lines have sufficient intensity levels. The pair of wavenumbers (5005.53 and 5003.3 cm$^{-1}$) is found the best of all for temperature and H$_2$O concentration distribution and 5004.36 cm$^{-1}$ is chosen for CO$_2$. To establish the efficacy of different reconstruction algorithms, the phantoms of bimodal and concentric temperature distribution with uniform concentration were tried with four reconstruction techniques. Impressive reconstructions were achieved for distribution of temperature and concentrations of H$_2$O and CO$_2$ for same types of phantoms using Filtered Landweber and Tikhonov regularization methods for 5005.53 and 5003.3 cm$^{-1}$. Initially the imaging was tried using both fanbeam and discrete irregular beam array with 100 and 31 beams respectively. Instead of less number of beams, the later one also shows very promising result.