Tomographic imaging of temperature and chemical species based on hyperspectral absorption spectroscopy

Abstract

A novel technique has been developed to obtain simultaneous tomographic images of temperature and species concentration based on hyperspectral absorption spectroscopy. The hyperspectral information enables several key advantages when compared to traditional tomography techniques based on limited spectral information. These advantages include a significant reduction in the number of required projection measurements, and an enhanced insensitivity to measurements/inversion uncertainties. These advantages greatly facilitate the practical implementation and application of the tomography technique. This paper reports the development of the technique, and the experimental demonstration of a prototype sensor in a near-adiabatic, atmospheric-pressure laboratory Hencken burner. The spatial and temporal resolution enabled by this new sensing technique is expected to resolve several key issues in practical combustion devices.

Laser diagnostics and minor species detection in combustion using resonant four-wave mixing

“…Multiplexing of multiple diode lasers and tomographic methods to achieve spatial resolution can provide multiple species and multiple parameter measurements [28]. In this context, the development of hyperspectral sources for absorption spectroscopy is providing a further tool for diagnostics of combustion environments [29][30][31].…”

“…Multiplexing of multiple diode lasers and tomographic methods to achieve spatial resolution can provide multiple species and multiple parameter measurements [28]. In this context, the development of hyperspectral sources for absorption spectroscopy is providing a further tool for diagnostics of combustion environments [29][30][31].In order to overcome the limitation of weak absorption several practical approaches have been developed to increase the effective absorption path using cavity enhancement. In this context intra-cavity laser absorption spectroscopy (ICLAS) has been used to enhance weak absorption signals.…”

Robust, spatially scanning, open-path TDLAS hygrometer using retro-reflective foils for fast tomographic 2-D water vapor concentration field measurements

“…These setups allow for very fast measurements, since all channels can be recorded simultaneously and the field measurement rate equals the rate at which the concentrations along each projection are measured. However, such highly parallel, bi-static setups either require large amounts of light-source-detectorpairs and the appertaining data acquisition channels (Wright et al, 2005;Terzija et al, 2008;Terzija and McCann, 2011;Ma et al, 2013) or are somewhat limited regarding spatial resolution (Ma et al, 2009;Deguchi, 2012). Additionally, a disadvantage of bi-static setups in field applications is the cumbersome alignment of many detectors.…”

Numerical and experimental validation of a three-dimensional combustion diagnostic based on tomographic chemiluminescence

“…First, combustion applications, due to optical access and the dynamic nature combustion processes, typically have limited number of projections available, ranges from 2 [25,26] to about 50 [20][21][22][23]27]. In contrast, other applications (e.g., medical imaging) have significantly more projections (thousands and more) available.…”

“…Well-established (and also mathematically exact) algorithms such as filtered back projection and Fourier reconstruction [24] do not work optimally with such limited projections available in combustion diagnostics. With the limited projections in combustion diagnostics, past results suggest that inversion method based on minimization can solve the tomography problem effectively in the presence of measurement noises [21,[26][27][28][29]. The tomography problem is cast into the following minimization problem: …”