H. McCann

The University of Edinburgh, Edinburgh, Scotland, United Kingdom

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Publications (88)66.3 Total impact

  • Chighine A · Tsekenis SA · Fisher E · McCann H
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    ABSTRACT: We present the design, implementation and testing of an FPGA-based, high-speed instrumentation system utilizing tunable laser diode absorption spectroscopy (TDLAS) in conjunction with wavelength modulation spectroscopy (WMS). By detecting the 1f and 2f harmonics of the absorption signal in the 1997nm region, we achieve accurate extraction of narrow absorption features of CO2 gas. Detection of the harmonics is performed by custom digital lock-in amplifier (DLIA) blocks, minimizing the cost per channel and the system’s size. Gas-cell experiments were performed to validate the performance of the implemented system against a high-end commercial DLIA. The comparison results show the systems are in good agreement, thus paving the way for extension of the current system to high channel-count, multi-projection Chemical Species Tomography (CST) applications.
    No preview · Conference Paper · Nov 2015

  • No preview · Conference Paper · Sep 2015

  • No preview · Conference Paper · Aug 2015
  • Source
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    ABSTRACT: Flame flatness is one of the most critical factors in evaluating the performance of a flat-flame burner. In this paper, the flame flatness of a flat-flame burner is validated using a resolution-doubled one-dimensional wavelength modulation spectroscopy tomography (1D-WMST) technique that only uses one view of multiple parallel laser beams. When the interval of two neighboring parallel laser beams is Δr, a designed novel geometry of the parallel laser beams realizes a doubled tomographic resolution of Δr/2. Using the proposed technique, the distributions of temperature and H2O mole fraction in an axisymmetric premixed flame are simultaneously reconstructed and hence the flame flatness of a flat-flame burner can be validated. The flatness factor is quantitatively described by the similarity between the reconstructed and expected distributions of H2O mole fraction. For flat and non-flat flames, the experimental results agree well with the CFD simulation results, denoting that the resolution-doubled 1D-WMST technique provides a noninvasive, reliable and low cost way to validate the flame flatness of the flat-flame burner.
    Full-text · Article · Jun 2015 · Applied Physics B
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    ABSTRACT: We report on the development of three systems intended to provide fast, non-intrusive measurement of cross-sectional distributions of pollutant species within gas turbine exhaust flows, during ground-based testing. This research is motivated by the need for measurement systems to support the introduction of technologies for reducing the environmental impact of civil aviation. Tomographic techniques will allow estimation of the distributions of CO2, unburnt hydrocarbons (UHC), and soot, without obstruction of the exhaust, bypass or entrained flows, from measurements made in a plane immediately aft of the engine. We describe a CO2 imaging system that performs wavelength modulation spectroscopy (WMS) simultaneously on 126 beam paths. Its novel architecture uses a Tm-doped fiber amplifier to generate sufficient optical power for the entire beam array (> 3 W) from a single 1997.2 nm diode-laser seed, reducing cost and enabling fully parallel detection and signal recovery. Various optical propagation issues are considered, including those arising from the varying degrees of interaction with the exhaust flow that exist within the beam array, as well as pointing errors arising from the limited rigidity of the measurement system's structure. We also report first steps towards a similar UHC measurement system, operating in the mid-infrared (MIR) region and targeting partially decomposed or oxidized fuel constituents, including formaldehyde and propene. Progress towards the chalcogenide glasses and fibers, needed for light delivery and/or amplification at these wavelengths is described. Finally, we report on the development status of a tomographic soot imaging system, based on laser induced incandescence (LII). We have demonstrated both long (192 ns) and short (17 ns) pulse variants of LII using fiber laser sources. Single path tests on a laboratory soot generator and, in the long pulse case, on a jet engine have confirmed that the energy and beam quality available from the fiber lasers is sufficient to enable an autoprojection approach, using just two intensified CCD cameras having 'near-orthogonal' views, with respect to the excitation laser.
    No preview · Article · Jun 2015 · IEEE Aerospace Conference Proceedings
  • S A Tsekenis · N Tait · H McCann
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    ABSTRACT: We present a novel framework and experimental method for the quantification of spatial resolution of a tomography system. The framework adopts the "black box" view of an imaging system, considering only its input and output. The tomography system is locally stimulated with a step input, viz., a sharp edge. The output, viz., the reconstructed images, is analysed by Fourier decomposition of their spatial frequency components, and the local limiting spatial resolution is determined using a cut-off threshold. At no point is an observer involved in the process. The framework also includes a means of translating the quantification region in the imaging space, thus creating a spatially resolved map of objectively quantified spatial resolution. As a case-study, the framework is experimentally applied using a gaseous propane phantom measured by a well-established chemical species tomography system. A spatial resolution map consisting of 28 regions is produced. In isolated regions, the indicated performance is 4-times better than that suggested in the literature and varies by 57% across the imaging space. A mechanism based on adjacent but non-interacting beams is hypothesised to explain the observed behaviour. The mechanism suggests that, as also independently concluded by other methods, a geometrically regular beam array maintains maximum objectivity in reconstructions. We believe that the proposed framework, methodology, and findings will be of value in the design and performance evaluation of tomographic imaging arrays and systems.
    No preview · Article · Mar 2015 · The Review of scientific instruments
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    ABSTRACT: Here we present the latest developments in tomographic imaging of gas turbine exhaust species, particularly CO2. The optical source, detection methodology and mechanical optical distribution design are discussed in detail.
    No preview · Article · Jan 2015
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    ABSTRACT: Here we present the latest developments in tomographic imaging of gas turbine exhaust species, particularly CO2. The optical source, detection methodology and mechanical optical distribution design are discussed in detail.
    No preview · Article · Jan 2015
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    ABSTRACT: Here we present the latest developments in tomographic imaging of gas turbine exhaust species, particularly CO2. The optical source, detection methodology and mechanical optical distribution design are discussed in detail.
    No preview · Article · Jan 2015
  • H. McCann · P. Wright · K. Daun
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    ABSTRACT: The tomographic imaging of chemical species distributions has undergone rapid development in the last 15. years, driven by the combination of key scientific and technological challenges, the emergence of new optoelectronic hardware, and fundamental progress in inverse problems. We describe here the state of the art in chemical species tomography using transmission-based spectroscopic absorption, as well as the key challenges for its future development. The treatment ranges from the infrared spectroscopy of target species and associated spectroscopic techniques, through hardware implementation in optical and electronic systems, to image reconstruction methods. Two case studies illustrate the application of central concepts in the field.
    No preview · Article · Jan 2015
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    Chang Liu · Lijun Xu · Zhang Cao · Hugh McCann
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    ABSTRACT: Fan-beam tunable diode laser absorption spectroscopy (TDLAS) system was combined with onion-peeling deconvolution to reconstruct axisymmetric temperature and gas concentration distributions. The fan-beam TDLAS system consists of two tunable distributed feedback diode lasers at 7185.597 and 7444.36 cm-1, a cylindrical lens and multiple photodiode detectors in a linear detector array. When a well-collimated laser beam penetrates through a cylindrical lens, a fan-beam laser was formed. Then, the fan-beam laser penetrates through the target region and is detected by the photodiode detectors in the detector array. After transforming the fan-beam geometry to equivalent parallel-beam geometry, axisymmetric temperature and gas concentration distributions can be reconstructed using the onion-peeling deconvolution. To obtain the reconstruction results with higher accuracy, a revised Tikhonov regularization method was adopted in the onion-peeling deconvolution. In this paper, numerical simulation and experimental verification were carried out to validate the feasibility of the proposed methods. The results show that the proposed methods can be used to on-line monitor the axisymmetric temperature and gas concentration distributions with higher accuracy and robustness in combustion diagnosis.
    Full-text · Article · Dec 2014 · IEEE Transactions on Instrumentation and Measurement
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    Edward Fisher · Andrea Chighine · Hugh McCann
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    ABSTRACT: The chemical combustion products and fuel burning to thrust performance of a jet engine, directly impacts the environmental friendliness of commercial aviation. The FLITES project (Fibre-Laser Imaging of Gas Turbine Exhaust Species) aims to complement engine design with a video-rate, spectrographically targeted, tomography system [1, 2, 5, 6]. This a) allows pre-shipment identification of engine problems, complementing the manufacturer’s own robust testing, b) allows engine optimization for efficient burning, c) enhances fuel mixture selection, and d) enables manufacturers to propose and test novel designs. The current work targets CO2 emissions using Tunable Diode Laser Absorption Spectroscopy (TDLAS) [2] in a 126 beam, 100fps tomographic system [6].
    Full-text · Conference Paper · Nov 2014

  • No preview · Conference Paper · Aug 2014
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    ABSTRACT: This article reports the application of optical tomography and chemical species tomography to the characterisation of the in-cylinder mixture preparation process in a gasoline, direct-injection, single-cylinder, motored research engine. An array of 32 near-infrared beams is transmitted in a horizontal plane across the cylinder bore near the top of the cylinder, through a circular quartz annulus. A novel approach to enable the optical alignment of the transmitting and receiving optics is utilised. The engine is operated at a stoichiometric condition at 1200 r/min, with negative valve overlap timing. Two tomographic measurement schemes (optical attenuation and chemically specific absorption) were used to acquire data on the spatial and temporal distribution of fuel throughout the engine cycle. Optimised data pre-processing methods are described for maximal beam count and data reliability. The presence of fuel during the intake stroke was detected by the optical beam attenuation due to scattering from the liquid gasoline droplets. Optical tomographic reconstruction of the spatial distribution of these droplets was achieved at an imaging rate of 7200 frames per second, revealing rapid intra-cycle spatial variations that were consistent between consecutive cycles. During the compression stroke, chemical species tomography images of fuel vapour were reconstructed from data acquired using chemically selective spectral absorption by the hydrocarbon molecules, at an imaging rate of 2400 frames per second. Later in the compression stroke, the temporal evolution of the fuel vapour distribution in the plane of observation is relatively slow and displays inhomogeneities that are consistent between consecutive cycles. This is the first report of the use of tomography to image, within individual engine cycles, the in-cylinder evolution of both fuel spray droplet distribution and fuel vapour distribution.
    No preview · Article · May 2014 · International Journal of Engine Research
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    ABSTRACT: We report on a pilot study of dynamic lung electrical impedance tomography (EIT) at the University of Manchester. Low-noise EIT data at 100 frames per second were obtained from healthy male subjects during controlled breathing, followed by magnetic resonance imaging (MRI) subsequently used for spatial validation of the EIT reconstruction. The torso surface in the MR image and electrode positions obtained using MRI fiducial markers informed the construction of a 3D finite element model extruded along the caudal-distal axis of the subject. Small changes in the boundary that occur during respiration were accounted for by incorporating the sensitivity with respect to boundary shape into a robust temporal difference reconstruction algorithm. EIT and MRI images were co-registered using the open source medical imaging software, 3D Slicer. A quantitative comparison of quality of different EIT reconstructions was achieved through calculation of the mutual information with a lung-segmented MR image. EIT reconstructions using a linear shape correction algorithm reduced boundary image artefacts, yielding better contrast of the lungs, and had 10% greater mutual information compared with a standard linear EIT reconstruction.
    No preview · Article · Apr 2014 · Physiological Measurement
  • N. Polydorides · W.R. Lionheart · H. McCann
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    ABSTRACT: The correctness of the two-dimensional reconstructed images obtained using Electrical Impedance Tomography has been a source of debate mainly due to the assumption that the electrostatic field is strictly confined within the electrodes' plane. In reality this is not correct because even if the electrodes are located in a plane arrangement, the electrostatic field they set up remains three-dimensional. Incorporating a 3D measurement volume, a realistic electrode model and a Newton based iterative technique we have investigated whether 3D images could be reconstructed when using plane electrode arrangements and 2D measurement protocols. After a series of simulated experiments we conclude that irrespectively of the number of parallel electrode rings mounted at the boundaries, unless 3D voltage measurements are captured no sensible images can be obtained. Exploring the significance of accurate modelling in EIT we also attempt to reconstruct some simulated 3D data using a simplistic 2D model aiming to validate the claim that 'no model conductivity consistent with measurement exists when the dimension is wrong' (Lionheart, 1999). At a further stage we look at some of the computational issues regarding 3D bulky reconstruction problems including the efficient computation of the forward solution and the Jacobian matrix. © 2014 International Society for Industrial Process Tomography.
    No preview · Article · Jan 2014
  • Paul Wright · Edward Fisher · Hugh McCann
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    ABSTRACT: We describe the optical design considerations for an optical tomography system operating in a jet exhaust plume. We identify the limitations of existing literature and describe laboratory and engine tests intended to address these.
    No preview · Conference Paper · Jan 2014
  • D. McCormick · M.G. Twynstra · K.J. Daun · H. McCann
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    ABSTRACT: This paper will describe the application of resolution matrices to the design of an optimised 126 beam, 6m absorption tomography array for imaging concentrations of CO2 in the exhaust plume of a Rolls-Royce Trent 1000 gas turbine engine. The resolution matrix will be used to define a fitness value, which is a function of the beam configuration, and is minimised by the optimal beam arrangement. Constraints ensure that the optimised beam arrangement can be implemented in a real tomography system. Genetic algorithms are used to determine the optimal array design from the large problem set.Results for image reconstructions of a quasi-realistic phantom of the exhaust plume for each of the array designs are presented with indications of the reconstruction errors. From the results, conclusions are drawn on the suitability of applying resolution matrices to the design of beam arrays for real limited-data tomographic systems. © 2014 International Society for Industrial Process Tomography.
    No preview · Article · Jan 2014
  • Z. Wu · H. McCann · L.E. Davis · A. Boughriet · A.T. Nugroho
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    ABSTRACT: An existing Newton-Kantorovich (NK) algorithm and a new Modified Newton-Kantorovich (MNK) algorithm are described for image reconstruction of dielectric objects. The reconstructed images using simulation and experimental data are also presented. The simulation results show that images of dielectric objects can be well reconstructed using both algorithms when the dielectric contrast, with respect to air, is relatively low. However, the MNK algorithm has a higher contrast limit and converges faster. The experimental study of a dielectric object at 2.45GHz using 16x16 views shows that the image of the experimental model can be well reconstructed using the MNK algorithm. © 2014 International Society for Industrial Process Tomography.
    No preview · Article · Jan 2014
  • Terzija N · McCormick D · McCann H · Alex Tsekenis
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    ABSTRACT: The user-friendly MATLAB-based TIPOD package provides fast, flexible analysis and image reconstruction of large volumes of chemical species tomography data. Initially focused on in-cylinder automotive applications, its scope has been extended and its design modified to permit easier modification and customization. The new version, TIPOD-2013, provides options for: data pre-processing (e.g. filtering, denoising); data referencing; quality-based data selection; image reconstruction (e.g. Landweber with median or wavelet filters, Tikhonov); off-line still-frame display; export to industry-standard video; and flexible simulation for development or validation of optimal sensor arrays. The key features of TIPOD-2013 are described, along with examples of its use. © 2014 International Society for Industrial Process Tomography.
    No preview · Conference Paper · Sep 2013