[Show abstract][Hide abstract] 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.
Applied Physics B 06/2015; 120(3). DOI:10.1007/s00340-015-6150-9 · 1.86 Impact Factor
[Show abstract][Hide abstract] 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.
IEEE Transactions on Instrumentation and Measurement 12/2014; 63(12):3067-3075. DOI:10.1109/TIM.2014.2315737 · 1.79 Impact Factor
[Show abstract][Hide abstract] 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)  in a 126 beam, 100fps tomographic system .
Laser Components 2nd International WORKshop on Infrared Technologies, Munich, Germany; 11/2014
[Show abstract][Hide abstract] 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.
International Journal of Engine Research 05/2014; 16(4). DOI:10.1177/1468087414544178 · 1.51 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
Applied Industrial Optics: Spectroscopy, Imaging and Metrology; 01/2014
[Show abstract][Hide abstract] ABSTRACT: We report on a pilot study with healthy subjects who had an MR scan in
addition to EIT data acquired with the Manchester fEITER system. The MR
images are used to inform the external shape of a 3D EIT reconstruction
model of the thorax, and small changes in the boundary that occur during
respiration are addressed by incorporating the sensitivity with respect
to boundary shape into a robust reconstruction algorithm. A quantitative
comparison of the image quality for different EIT reconstructions is
achieved through calculation of their mutual information with a
segmented MR image. A shape corrected reconstruction algorithm reduces
boundary artefacts relative to a standard reconstruction, and has a
greater mutual information of approximately 4% with the segmented MR
Journal of Physics Conference Series 04/2013; 434(1):2082-. DOI:10.1088/1742-6596/434/1/012082
[Show abstract][Hide abstract] ABSTRACT: A novel opto-electronic scheme for line-of-sight Near-IR gas absorption measurement based on direct absorption spectroscopy (DAS) is reported. A diode-laser-based, multiwavelength system is designed for future application in nonintrusive, high temporal resolution tomographic imaging of H<sub>2</sub>O in internal combustion engines. DAS is implemented with semiconductor optical amplifiers (SOAs) to enable wavelength multiplexing and to induce external intensity modulation for phase-sensitive detection. Two overtone water transitions in the Near-IR have been selected for ratiometric temperature compensation to enable concentration measurements, and an additional wavelength is used to account for nonabsorbing attenuation. A wavelength scanning approach was used to evaluate the new modulation technique, and showed excellent absorption line recovery. Fixed-wavelength, time-division-multiplexing operation with SOAs has also been demonstrated. To the best of our knowledge this is the first time SOAs have been used for modulation and switching in a spectroscopic application. With appropriate diode laser selection this scheme can be also used for other chemical species absorption measurements.
[Show abstract][Hide abstract] ABSTRACT: A novel and effective methodology of combining images obtained by both electrical impedance tomography (EIT) and magnetic resonance imaging (MRI) data is described. Co-registered and fused image results for an example laboratory phantom based on the polysaccharide gel TX151 are presented. Bespoke software was used to convert an EIT dataset into a form consistent with 3D-Slicer, a powerful software package used for visualisation and image analysis. The data fusion provides a highly effective method of directly comparing EIT images, which typically have good temporal resolution and relatively poor spatial resolution, with those obtained with MRI, which has relatively poor temporal resolution but excellent spatial resolution.
[Show abstract][Hide abstract] ABSTRACT: The concept of Agile Tomography is introduced and exemplified by reviewing the progress in tomography sensors and systems which can be deployed in situ. Agile tomography capabilities are examined across a number of electromagnetic and electrical modalities, ranging from gamma-rays to low-frequency electrical measurements. The recent achievements in already established areas are highlighted, as well as emerging technology and new modalities.
[Show abstract][Hide abstract] ABSTRACT: We introduce a new wavelet-based hard-field image reconstruction method that is well suited for data inversion of limited path-integral data obtained from a geometrically sparse sensor array. It is applied to a chemical species tomography system based on near-IR spectroscopic absorption measurements along an irregular array of only 27 paths. This system can be classified as producing severely limited data, where both the number of viewing angles and the number of measurements are small. As shown in our previous work, the Landweber iteration method allows stable solution of this tomography problem by incorporating suitable a priori information. In the new method, a 2-D discrete wavelet transform has been used as a smoothing function. We present a method of designing the optimal wavelet-based smoothing function, depending on a priori knowledge of the subject. The significance of the particular wavelet filter selected is considered in terms of the accuracy of reconstruction of the spatial location and shape of the gas distribution. Results are presented for simulated phantoms using different sensor arrays and for experiments with propane plumes, showing excellent spatial localization and quantification. The computational time of the iterative algorithm is significantly reduced by applying the wavelet transform method. Some of our conclusions are applicable to other hard-field tomographic modalities in applications where similar constraints may be encountered.
[Show abstract][Hide abstract] ABSTRACT: In many dynamic gas-phase reaction processes, there is great interest to measure the distribution of minor constituents, i.e. <10−3 by volume (1000 ppm). One such case is the after-treatment of automotive gasoline engine exhaust by catalytic conversion, where a characteristic challenge is to image the distribution of 10 ppm (average) of carbon monoxide (CO) at 1000 frames per second across a 50 mm diameter exhaust pipe; this particular problem has been pursued as a case study. In this paper, we present a novel electronic scheme that achieves the required measurement of around 10−3 absorption with 10−4 precision at kHz bandwidth. This was not previously achievable with any known technology. We call the new scheme Auto-Digital Gain Balancing. It is amenable to replication for many simultaneous measurement channels, and it permits simultaneous measurement of multiple species, in some circumstances. Experimental demonstrations are presented in the near-infrared. In single scans of a tunable diode laser, measurements of both CO and CO2 have been made with 20 dB signal-to-noise ratio at peak absorption. This work paves the way for chemical species tomography of minor constituents in many dynamic gas-phase systems.
[Show abstract][Hide abstract] ABSTRACT: Electrical Impedance Tomography (EIT) can resolve dynamic physiological information deep within human subjects , but its sensitivity is challenged in the case of imaging the head . Here, we report a new system called fEITER that has been designed and built to enable functional imaging of the human brain using EIT via scalp-mounted electrodes, integrated with stimulation of evoked responses. Using Field-Programmable Gate Array (FPGA) technology, it provides excellent flexibility in terms of current-pattern excitation and signal processing. The instrument operates at 100 frames/second (fps) with noise of 1 μV on the rms voltage measurements. Clinical trials have been authorized by the UK MHRA and example data from human subjects are presented.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2011; 2011:7029-32. DOI:10.1109/IEMBS.2011.6091777
[Show abstract][Hide abstract] ABSTRACT: We report on human tests of the new EIT-based system fEITER (functional Electrical Impedance Tomography of Evoked Responses), targeted principally at functional brain imaging. It is designed and built to medical standard BS EN 60601-1:2006 and clinical trials have been approved by the MHRA in the UK. fEITER integrates an EIT sub-system with an evoked response sub-system capable of providing visual, auditory or other stimuli, and the timing of each stimulus is recorded within the EIT data to a resolution of 500 microseconds. The EIT sub-system operates at 100 frames per second using 20 polar/near-polar current patterns distributed among 32 scalp electrodes that are arranged in a 3-dimensional array on the subject. Presently, current injection is fixed in firmware at 1 mA pk-pk and 10 kHz. Performance testing on inanimate subjects has shown voltage measurement SNR better than 75 dB, at 100 frames per second. We describe the fEITER system and give example topographic results for a human subject under no-stimulus (i.e. reference) conditions and on application of auditory stimuli. The system's excellent noise properties and temporal resolution show clearly the influence of basic physiological phenomena on the EIT voltages. In response to stimulus presentation, the voltage data contain fast components (~100 ms) and components that persist for many seconds.
Journal of Physics Conference Series 04/2010; 224(1). DOI:10.1088/1742-6596/224/1/012025
[Show abstract][Hide abstract] ABSTRACT: We report here the first application of chemical species tomography (CST) in a multi-cylinder automotive engine. This technique offers high-speed continuous imaging of hydrocarbon fuel distribution and mixing within the combustion chamber and is therefore of interest to both engine designers and combustion scientists. Many of the methods described are equally applicable to chemically selective imaging of other highly dynamic mixing and reaction processes.A measurement grid consisting of 27 dual-wavelength optical paths has been implemented in one cylinder of an otherwise standard four-cylinder port-injected gasoline engine, using a unique OPtical Access Layer (OPAL) carrying embedded optical fibres and collimators. The OPAL provided adequate performance on many beams for more than 2 h of fired engine operation. To improve sensitivity and to cope with fuel spray injection directly into the cylinder (in other engine types), a low-noise opto-electronic system has been developed, offering laser intensity modulation at frequencies up to 1 MHz. Dual-wavelength measurements are recorded on each channel at 100 kSPS, prior to off-line processing that typically reduces the effective frame rate to 3000–4000 frames/s, dependent upon engine speed. The performance of the system is assessed, using running conditions chosen to provide a qualitatively known (homogeneous) fuel distribution for validation purposes. Examples of measured data and processing schemes are discussed. Sample tomographic images, obtained using a novel quality-based approach to data selection, are presented.
Chemical Engineering Journal 03/2010; 158(1-158):2-10. DOI:10.1016/j.cej.2008.10.026 · 4.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Since the early 1980s, a number of electrical imaging techniques based on capacitance, resistance, or inductance measurement at low frequencies have been developed for the monitoring of industrial processes, such as oil- and gas-multiphase flows. In principle, microwave tomography would produce higher resolution images than these low-frequency techniques. But it has mainly been studied for medical applications over the past two decades and is less developed for industrial applications. In this paper, the development of an experimental microwave-tomography system intended for oil- and gas-flow measurements is described, which includes the hardware for data acquisition and the numerical algorithm for image reconstruction. The investigation of the system for the imaging of static–dielectric phantoms modelling oil- and gas-flow distributions is reported together with the images obtained at two different microwave frequencies: 2.5 GHz and 4 GHz. It has been demonstrated that images of the dielectric phantoms can be reconstructed using the system, with the images obtained at 4 GHz having better quality and higher resolution.
[Show abstract][Hide abstract] ABSTRACT: High-speed Chemical Species Tomography (CST) using near-IR absorption has recently been demonstrated in a multi-cylinder gasoline SI engine running on retail fuel. Many of the inherent advantages of the CST technique would be even more marked in CI engines, for example in HCCI engines where mixture preparation involves residual spe-cies, and in diesel engines where gross inhomogeneities over large spatial scales are the norm. On the basis of prac-tical experience of CST in engines and in laboratory systems, this paper explores the potential for these applications of the technique. Introduction There is a long-term trend towards greater pre-mixing of fuel and air in compression ignition (CI) engines. The most extreme case is the Homoge-neous Charge Compression Ignition (HCCI) engine . Even in the "conventional" diesel engine, injec-tion sequences now lead to complex mixture de-velopment processes. Moreover, the creation of engine-out pollutant species is of critical impor-tance. These trends demand in-cylinder imaging of chemical species in a variety of CI engine types. The technique of Chemical Species Tomo-graphy (CST) has recently emerged due to the maturing of Near-Infra-Red (Near-IR) opto-electronic technologies that were initially used in the communications industry: diode lasers, optical fibres with mixers and splitters, and photodiodes. The keys to exploiting these technologies are low noise opto-electronic schemes for spectroscopic measurements, and beam array design for ade-quate spatial resolution. For high-speed imaging of hydrocarbon fuel in a gasoline SI engine cylinder, the Manchester group has developed an imple-mentation of Near-IR CST (Fig. 1) that has al-lowed, to date, up to 32 simultaneous path-integral measurements through the measurement subject [2-4]. This paper discusses the application of CST to CI engines in projects that are now underway.
[Show abstract][Hide abstract] ABSTRACT: Ultra-sensitive detection of minor species is important in many fields. The requirement of direct online measurement of gas species in process engineering motivates fast measurements over short pathlengths. The resulting high bandwidth and low absorptions reduce the measurement Signal-to-Noise Ratio (SNR). Our target is to detect CO in engine exhaust with sensitivity of the order of 0.05 ppm-m at several kHz. In this paper, a novel electronic scheme is discussed and presented with simulation results. A generic approach is followed, to use it with either a pulsed or a continuous wave (CW) laser source. A detailed noise analysis is presented for improved understanding of the SNR of the overall scheme.
Electronics, Circuits and Systems, 2008. ICECS 2008. 15th IEEE International Conference on; 10/2008
[Show abstract][Hide abstract] ABSTRACT: In order to develop a chemical species tomography system, this paper carries out various computational steps to address the problem of measuring minor species concentration using single-pass, short path-length absorption techniques in the mid-infrared. It focuses on the imaging of carbon monoxide (CO) in combustion exhaust as a case study, with an average concentration of 10 ppm over a 50 mm diameter cross-section, taking account of the presence of other absorbing species. CO absorption transitions R6, R7, R9 and R10 are identified as possible measurement targets. The joint effects of spectral absorption linewidth and laser source linewidth are considered at length, resulting in recommendations for laser linewidth to achieve appropriate levels of CO absorption signal purity. Measurement strategies are considered for achievement of the necessary sensitivity, noise and bandwidth performance. A feasible beam arrangement for tomographic imaging is discussed, providing 48 measurements of path concentration integral. Representative phantom reconstructions are presented, with encouraging results for application to such dynamic gaseous subjects.