Simulation of 2D tomographic TDLAS using algebraic reconstruction and Tikhonov regularization

Document Type

Conference Proceeding

Publication Date

1-1-2013

Abstract

Tomographic techniques allow for the reconstruction of spatially varying temperature and concentration fields in a flame from line-of-sight integrated tunable diode laser absorption spectroscopy (TDLAS) measurements. Such methods generally need data taken from a large number of view angles to gather as much directional information about the property distribution inside the flame as possible. Often, optical access for such measurements is limited, which poses substantial problems for conventional tomographic methods. In recent years, hyper-spectral approaches have shown promising results, where the lack of directional information is compensated by increased spectral information from wide-band tunable lasers. This work uses an alternative approach for tomographic reconstruction that uses conventional DFB diode lasers with narrow tunability, which are commonly used for line-of-sight TDLAS measurements. Specifically, the feasibility of performing limited-view tomographic reconstruction using tunable diode laser absorption spectroscopy (TDLAS) for temperature and concentration of water vapor in a stationary flame is addressed. Simulated TDLAS line-of-sight (LOS) data consist of second harmonic peak heights (2f) obtained from wavelength modulation. Ratio thermometry from twotransition technique is used to infer local temperature and concentration of the species in the flame. Integrated absorption measurements in the near-IR region (6930 cm-1 to 6940 cm-1 range) are simulated to obtain projection values from tomography. Spectroscopic parameters such as line-strengths, transition wave numbers, collisional broadening coefficients and coefficients for their temperature dependency are taken from the HITRAN 2008 database. Two tomographic de-convolution methods are chosen - a) a multiplicative algebraic reconstruction technique (MART), which is known to perform much better than traditional filtered-backprojection algorithms in case of limited-view tomo-synthesis and b) a Tikhonov regularized tomographic inversion. In both cases, tomographic algorithms are used to reconstruct local 2f peak height distribution for two spectroscopic transitions and temperature and concentration of water vapor are determined and compared to assumed model distributions.

Publication Source (Journal or Book title)

8th US National Combustion Meeting 2013

First Page

3319

Last Page

3332

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