Tomographic measurement of breakthrough in a packed bed adsorber

Laser-absorption tomography beam arrangement optimization using resolution matrices

Laser-absorption tomography experiments infer the concentration distribution of a gas species from the attenuation of lasers transecting the flow field. Although reconstruction accuracy strongly depends on the layout of optical components, to date experimentalists have had no way to predict the performance of a given beam arrangement. This paper shows how the mathematical properties of the coefficient matrix are related to the information content of the attenuation data, which, in turn, forms a basis for a beam-arrangement design algorithm that minimizes the reliance on additional assumed information about the concentration distribution. When applied to a simulated laser-absorption tomography experiment, optimized beam arrangements are shown to produce more accurate reconstructions compared to other beam arrangements presented in the literature.

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

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.

Digitally balanced detection for optical tomography

Analog balanced Photodetection has found extensive usage for sensing of a weak absorption signal buried in laser intensity noise. This paper proposes schemes for compact, affordable, and flexible digital implementation of the already established analog balanced detection, as part of a multichannel digital tomography system. Variants of digitally balanced detection (DBD) schemes, suitable for weak signals on a largely varying background or weakly varying envelopes of high frequency carrier waves, are introduced analytically and elaborated in terms of algorithmic and hardware flow. The DBD algorithms are implemented on a low-cost general purpose reconfigurable hardware (field-programmable gate array), utilizing less than half of its resources. The performance of the DBD schemes compare favorably with their analog counterpart: A common mode rejection ratio of 50 dB was observed over a bandwidth of 300 kHz, limited mainly by the host digital hardware. The close relationship between the DBD outputs and those of known analog balancing circuits is discussed in principle and shown experimentally in the example case of propane gas detection.

Toward in-cylinder absorption tomography in a production engine

Design requirements for an 8000 frame/s dual-wavelength ratiometric chemical species tomography system, intended for hydrocarbon vapor imaging in one cylinder of a standard automobile engine, are examined. The design process is guided by spectroscopic measurements on iso-octane and by comprehensive results from laboratory phantoms and research engines, including results on temporal resolution performance. Novel image reconstruction techniques, necessary for this application, are presented. Recent progress toward implementation, including details of the optical access arrangement employed and signal-to-noise issues, is described. We present first cross-cylinder IR absorption measurements from a reduced channel-count (nontomographic) system and discuss the prospects for imaging.