The LITECS Programme Grant https://www.litecs.uk
The ultimate ambition of the LITECS research programme is to reduce the environmental impact of aviation and industrial gas turbine engines, through development and deployment of new measurement technologies to enhance understanding and modelling of combustion and emissions generation processes and the role of alternative fuels.
These new technologies will revolutionise the measurement of gaseous and particulate combustion species and provide spatially and temporally resolved maps of strategic high priority species such as soot, CO2, CO, water and NO. The instrumentation systems developed by Strathclyde, Edinburgh and Manchester Universities will be installed on combustion research rigs at NCCAT (Loughborough) and LCCC (Sheffield) for experimental GTE research in this programme and far into the future. The instrumentation development programme focuses on tuneable diode laser spectroscopy (TDLS) as the basic measurement technique for gaseous species, laser induced incandescence (LII) for soot, multiple beam TDLS for tomographic species imaging and beam scanning for soot imaging. Southampton University is developing the new near-infra red (NIR) and mid-infrared (MIR) technology required for light amplification and delivery.
LITECS, led by Professor Walter Johnstone of the University of Strathclyde, is funded by an £8M EPSRC Programme Grant (including the contributions from Industry and the academic partners). It started in September 2020 with an end date of August 2024. Industry partners are Rolls-Royce (aero-engine manufacturer), Siemens (industrial gas turbine engine manufacturer), OptoSci Ltd (a laser instrumentation manufacturer), M Squared lasers and Tracerco (imaging systems manufacturers). LITECS is the latest, and largest, of a sequence of related research grants on turbine diagnostics, starting with the EPSRC-funded FLITES consortium (2012-17), which was continued by the EU Cleansky2 CIDAR project coordinated by INTA (Madrid) (2018-date). Starting in 2016, the CIDER Platform Grant has made seminal contributions to enable the growth of this sequence.
Turbulent multiphase flow - Fuji Electric
A long-standing challenge is to measure accurately the key parameters of turbulent multiphase flow at industrial scale, such as velocity, void fraction and mass flow rate. In February 2019, after a competitive worldwide tender, Fuji Electric Co. Ltd., a Japanese electrical equipment corporation, invested £300k for a commissioned research study led by Jiabin Jia. With Paul Tait working on it full-time, experimental campaigns were carried out in the wet-gas facility at TUV National Engineering Laboratory(NEL) in August 2019 and the wet-steam facility at Spirax Sarco at Cheltenham in October 2020.
The team has developed a low-cost and non-intrusive solution for wet-gas flow metering. The promising experimental results encourage the industrial funder to continue the field testing stage. Ultimately, Fuji Electric aims to utilise this novel metering solution in renewable energy settings.
The project team from Edinburgh1 and Fuji Electric2 visiting TUV NEL at East Kilbride, Scotland:
from left, Yasuo Inamura2, Wataru Senjyu2, Paul Tait1, Toru Watanabe2, and Jiabin Jia1
Clean Sky 2 – Combustion species Imaging Diagnostics for Aero-engine Research (CIDAR)
The Edinburgh and Strathclyde groups have launched a new project to perform pioneering in situ imaging of chemical species and non-volatile particulates (nvPM) in full-scale aero-engine exhausts and to increase the TRL level of the measurement systems developed in the EPSRC FLITES project. Chemical Species Tomography (CST) will be used to map the output of CO2 from the engine core exhaust, and a technique based on laser-induced incandescence (LII) will enable 2D measurement of exhaust nvPM concentration. The project is funded through the EU Clean Sky 2 programme and is carried out in partnership with INTA, the Spanish National Aerospace Institute (coordinator) the University of Manchester, DAS Photonics (Valencia) and OptoSci, coordinating closely with Rolls-Royce. This combined technological development in CIDAR (pronounced “theedar” in Spanish) will produce an innovative step change in full-scale aircraft engine diagnostics, based on real-time, in-situ photonic technologies.
Energy transfer processes at gas/wall interfaces
High-efficiency low-CO2 vehicles will soon be powered by down-sized IC engines operating at higher pressures. These concepts raise challenges such as transient heat transfer and flame quenching near surfaces. In a new ERC-funded project, Brian Peterson focuses on the development of laser diagnostics to study transient boundary layer phenomena relevant to engine environments. Using a unique combination of high-speed SO2 laser-induced fluorescence (LIF) and particle tracking velocimetry (PTV), measurements in an optically accessible engine reveal the transient boundary layer development in response to an approaching flame front (left figure). A strong interdependence is observed between near-wall flow and flame development, which appears to influence subsequent combustion. An approaching flame results in flow acceleration, which decreases the boundary layer thickness δ75, as shown in the right figure. These subtle effects increase convective heat loss and influence reaction rates near walls, with major impact on engine performance.
Further information: Proceedings of the Combustion Institute doi:10.1016/j.proci.2018.06.215
Major facility investment
Holographic imaging of surrogate micro-drop
Hybrid fs/ps rotational coherent anti-Stokes Raman spectrum at high pressure, measurement and spectral fit.
The Clean Combustion group has won an EPSRC Strategic Equipment Grant which, along with other grants, is being used to establish a world-leading research facility with:
- three 10,000 fps cameras with 2 image intensifiers;
- 10 KHz pulsed Nd:YAG laser (2-pulse, for fast PIV);
- 10 KHz pulsed Nd:YAG laser (multi-wavelength for high-speed Planar LIF);
- 1 kHz, 35 fs pulsewidth Ti:sapphire regeneratively amplified laser;
- 50 Hz, 30 ps pulsewidth Nd:YAG regeneratively amplified laser;
- two, 2-pulse 10 Hz Nd:YAG laser setups (for 4 pulses) to pump two tunable dye laser systems;
- two 6W cw lasers (1 multi-mode and 1 single frequency);
- phase Doppler interferometer; and
- ancillaries such as detectors, spectrometers, imagers, optics, etc.
This equipment will be applied to a high-pressure chamber for spray research, an optically accessible research engine, and many other flow devices. Examples of recent work using these systems are shown here.
Laser and Fibre Optic Gas Absorption Spectroscopy
NEW BOOK PUBLISHED
Building on previous expertise and on research performed under the CIDER platform grant, a new book has recently been completed and published in April 2021 by Cambridge University Press on the topic of ‘Laser and Fibre Optic Gas Absorption Spectroscopy’, one of the four major themes of the CIDER research programme.
The book brings together the fundamental principles of spectroscopy, laser physics and photonic engineering to facilitate the design of gas sensors based on absorption spectroscopy. In particular, there is an extensive account of the properties of DFB diode lasers, providing an in-depth understanding of the key tuning characteristics that are especially relevant in the design of spectroscopic systems for line shape recovery and for measurement of the concentration, pressure or temperature of the target gas. There is also an extensive review of the theory, techniques and applications of wavelength modulation spectroscopy, many of which have been developed, tested or applied within the research programmes performed under the CIDER platform grant. Other topics discussed include photoacoustic spectroscopy, frequency comb spectroscopy, silicon photonic gas sensors and an overview of the state-of-the art of mid-IR spectroscopy and comparison with near-IR gas sensor systems.
In addition, there are a number of resources which have been made available with this book, including Matlab programmes to simulate the theoretical output signals from gas sensors under various conditions of operation and PowerPoint presentations for each chapter to highlight the key ideas and for teaching purposes. The book should be a useful resource for new researchers entering the field as well as providing a stimulus for further research into the diverse techniques and applications of laser absorption spectroscopy.
Cambridge University Press, April 2021, ISBN: 9781107174092
Further information: www.cambridge.org/stewart
Thermal boundary layers and heat transfer
Heat loss at gas/wall interfaces plays an important role for the design of cleaner combustion engines, particularly for small engine geometries intended for hybrid-electric platforms. The accuracy with which transient heat losses can be predicted at walls is determined by the ability to resolve the thermal boundary layer. The work of David Escofet-Martin et al. takes advantage of hybrid rotational coherent anti-Stokes Raman spectroscopy (HRCARS) to measure single-shot, wall-normal gas temperatures, which provide exclusive access to the thermal boundary layer. HRCARS is combined with thermographic phosphors for simultaneous gas and wall temperature measurements. With this, we are able to record the time-history of important boundary layer quantities and wall heat flux during three types of transient event: polytropic compression, flame-wall interaction, and post-flame cooling.
Further information: Proc. Combust. Inst. doi:10.1016/j.proci.2020.06.097
Dual-probe CARS for simultaneous temperature, pressure, and O2 concentrations
Understanding turbulent, thermal flows requires sophisticated diagnostics that can measure several variables of interest. This often requires application of multiple diagnostic techniques, which may be limited in spatial-temporal resolution. We have developed a new approach to measure gas temperature, pressure and O2 concentrations simultaneously from a single diagnostic. This comprises of a dual-probe 1D hybrid-rotational coherent anti-Stokes Raman spectroscopy (HRCARS) approach, which utilizes the time- and frequency-domain to measure the three variables. What is particularly novel is utilising a ratio method of the CARS signals from the two probe-pulses to yield 1D pressure measurements with exceptional spatial resolution (60 μm) and measurement precision (0.42%). Measurements have resolved single-shot pressure gradients (0.04 bar/mm) originating from kinetic energy conversion to pressure (i.e. stagnation pressure field) as a flow impinges onto a surface.
Further information: Optics Letters doi:10.1364/OL.400595
RETRO algorithm for robust temperature imaging in CST
High-fidelity temperature imaging is of critical interest in the application of Chemical Species Tomography (CST). The temperature image is generally obtained from the reconstructed absorbance distributions for two spectral transitions. However, the inherently ill-posed nature of tomographic data inversion leads to noise in each of the reconstructed absorbance distributions. These noise effects propagate into the absorbance ratio and generate artefacts in the retrieved temperature image. To address this problem, Yong Bao et al. have developed a novel algorithm, which we call Relative Entropy Tomographic RecOnstruction (RETRO), for CST. A relative entropy regularisation is introduced for high-fidelity temperature image retrieval from jointly reconstructed two-line absorbance distributions.
The images here show:
|Top||-||an experimental phantom consisting of two burner flames;|
|Middle||-||reconstruction of the flame temperature using the conventional Simultaneous Algebraic Reconstruction Technique (SART); and|
|Bottom||-||reconstruction of the flame temperature using RETRO.|
RETRO exhibits excellent robustness against tomographic measurement noise, offering great potential for industrial field applications of CST in very harsh environments.
Further information: IEEE Trans. Inst. & Meas. doi:10.1109/TIM.2020.3037950
Cost-effective quasi-parallel DAQ for Chemical Species Tomography
Parallel data acquisition (DAQ) is necessary to maximise temporal resolution in multi-beam CST systems. However, it leads to a highly complex and power-consuming instrumentation system, and a significant burden on data transfer infrastructure. To address these issues, Godwin Enemali et al. developed a quasi-parallel (QP) DAQ system for industrial applications of CST, in which the digitisation and demodulation of the multi-beam signals are multiplexed between periods of the high-frequency modulation within a wavelength scan. The proposed scheme facilitates cost-effective implementation of industrial CST with very low complexity and reduced load on data transfer compared to the fully parallel sensing technique. The image shows the flowchart of the QP sensing scheme demonstrated for four-beam multiplexing.
Further information: IEEE Trans. Ind. Electron. doi:10.1109/TIE.2021.3063963
Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering (HR-CARS) at high temperature and pressure
In a recent collaboration between the University of Edinburgh and Sandia National Laboratories, we have demonstrated the use of HR-CARS as a technique for temperature measurements in nitrogen gas at high pressures and temperatures. Broadband, pulse shaper-adjusted 42 fs Stokes/pump pulses interacted with a narrow-bandwidth, frequency-upconverted 5.5 ps probe pulse in a cell containing N2 at pressures of 1–70 atm. and temperatures of 300–1000 K. A computational code was developed to model the spectra and fit experimental results, to obtain best-fit temperatures. We demonstrated good quality fits, with good accuracy and precision, between thermocouple measured and best-fit temperatures over the explored pressure and temperature range. The overall average percentage temperature difference between thermocouple measurements and best-fit temperatures was −0.3% with a standard deviation of 7.1%, demonstrating the suitability of HR-CARS for characterizing high temperature and pressure environments. In addition, by use of very broadband (fs) Stokes/pump pulses for rotational CARS, one can simplify phase matching and acquire high fidelity temperature measurements along a line with excellent spatial resolution (in the order of 50 µm).
Further information: Journal of the Optical Society of America B doi:10.1364/JOSAB.383575
New engineering design rules for CST systems
A new paper from the Edinburgh Agile Tomography group shows how to design Chemical Species Tomography systems to achieve a target spatial resolution (δ). The numbers of beams and projections (“views”) are optimised whilst minimising the total number of beams, for which there is no useful theoretical guidance. A large number of beam arrangements were simulated, as realistically as possible, in the context of in-cylinder imaging for diesel engines, and δ calculated using our previously published method. The figure here shows how δ varies as the beam array is changed: there is very little benefit of having more than about 4 or 5 views, or 20-25 beams per view. Using a “phantom” comprising real engine spray images obtained by Planar Laser-Induced Fluorescence, a 4x25 array was found to perform better than arrays 3x34 and 5x20, offering δ values of 3 mm or less for an 80 mm-diameter cylinder bore.
Further information: IEEE Sensors J. (accepted) doi:10.1109/JSEN.2018.2884085
CST reveals beautiful swirl flame behaviour
Swirl combustion is critically important for operation of gas-turbine aero engines, but the dynamic flame chemistry has not previously been accessible with spatio-temporal resolution. Using Chemical Species Tomography (CST) of combustion-produced water, Chang Liu has overcome this barrier and discovered the elegant behaviour of the flame. The three still images here show the temperature distribution of the water at 12 ms intervals. The swirling precession of the most intense flame region, which is easily visible as an anti-clockwise rotation in the images, is found to be highly stable. The movie shows the dynamics of lean blow-out (LBO) as the fuel supply rate is reduced. Measurements such as these could be used to detect swirl flame instabilities so that fuel supply can be modified actively to prevent LBO. This work is an example of the on-going collaboration between the Edinburgh group and Prof. Lijun Xu’s group at Beihang University, Beijing.
Further information:IEEE Trans. Inst. & Meas. doi:10.1109/TIM.2018.2799098
A New Calibration-Free Approach to TDLS-WMS
The Strathclyde team has published a new 1f/1f normalisation technique that is calibration-free and potentially superior to the technique of dividing two different harmonic spectra (e.g. 2f/1f) in wavelength modulation spectroscopy (WMS). Being calibration-free, 2f/1f has been widely used to measure gas species concentrations in harsh environments. Led by Michael Lengden, the team were using 2f/1f to measure CO2 concentration at the exhaust of a swirl combustor, and data analysis revealed discrepancies with results obtained using extractive NDIR measurements. The source of the problem was the MCT detector, which showed a frequency-dependent, highly non-linear output as a function of incident optical power. Requiring only the 1f signal, the strongest of all the harmonic signals, the new technique fundamentally has higher sensitivity than nf/1f. It is also less complex in terms of signal processing and data acquisition, ideal for multi-beam systems. The figure shows example results of 1f/1f, compared with NDIR and 2f/1f.
Further information: IEEE Photonics J. doi:10.1109/JPHOT.2018.2883548
Key CCS process penetrated by ECT
Carbon Capture and Storage (CCS) uses CO2 absorption by amine solvents in a packed column. This is a complicated hydromechanical process which is difficult to optimise in operation. In an EPSRC-funded project in collaboration with a CCS specialist group, Jiabin Jia has adapted Electrical Capacitance Tomography (ECT) to tackle this problem. The new approach enabled the team to analyse the distribution of a liquid phase across the packing of a counter current gas-liquid column with Sulzer Mellapak 250 Y packing and to quantify the liquid hold-up. The images here show how the liquid distribution can be manipulated simply by changing the orientation of the specialist packing material (rotation by 90 degrees in this case). Most importantly, the experimental results give confidence in using ECT in field service to provide measurements of the real-time liquid distribution and local liquid hold-up, thus enabling process optimisation.
Further information: Chemical Engineering Journal doi:10.1016/j.cej.2018.07.016
New members of academic team
We are excited by the recruitment of several new staff and research students whose work will greatly enhance the output of the CIDER themes:
Yinghao Li joined the Agile Tomography group in Edinburgh as a PhD student in September 2018. He obtained his BEng dual degree from The University of Edinburgh and North China Electric Power University in June 2018. His PhD project focuses on gesture recognition and tracking using ultrasound. The combination of ultrasonic waves and machine learning algorithms has the potential to recognise hand movement as a new form of human-machine interface. Yinghao is particularly interested in signal processing and pattern recognition.
Zhixi Zhang started as a PhD student in the Agile Tomography group in Edinburgh in September 2018. She obtained the BEng degree from the School of Engineering in July 2018. Zhixi’s research will produce a prototype control system to track the movement of lung tumours using electrical impedance tomography (EIT). Her aim is to develop a new image-guided radiotherapy method to improve the precision and accuracy of treatment delivered to tumours in areas of the body that move. Real-time EIT images will be used to control radiotherapy beams to enhance the effective radiation dose and avoid damage to healthy surrounding tissue.
Hibbah Ahktar started in the Clean Combustion Group in Edinburgh as a PhD student in September 2018. She obtained her Bachelor’s and Master’s degrees in Power Engineering from the University of Engineering and Technology Lahore in Pakistan, where she focused on soot reduction for gasoline direct-injection vehicles. At Edinburgh, in collaboration with Innospec, she is studying the effect of fuel additives on injector performance, for reduction in soot emission in gasoline engines.
Godwin Enemali started in the Agile Tomography Group in Edinburgh, in the role of Post-Doctoral Researcher on the Clean Sky 2 CIDAR project, in January 2019. He obtained his Bachelor’s degree in Nigeria, followed by two degrees from the School of Engineering in Edinburgh: MSc in Electronics, and PhD in Adaptive High-Performance Digital Systems. In CIDAR, Godwin is developing the data acquisition system for CO2 CST, working closely with Strathclyde and DAS Photonics. He is particularly interested in FPGA Architectures, and Reliable and Parallel Sensor Data Processing.
Andrew Gough joined the Centre for Microsystems and Photonics in the Department of Electronic and Electrical Engineering at the University of Strathclyde in 2018, as a PhD student. He obtained his integrated MPhys in Physics from Strathclyde in 2017. His PhD project focuses on temperature measurements using Tunable Diode Laser Spectroscopy to enable further understanding of entropy waves in reactive flows.
Lars Christian Johansen joined the Clean Combustion Laboratory in Edinburgh at the end of 2017, as Experimental Officer. He gained Bachelors and Masters degrees at Aalborg University, Denmark, in Fluids, Thermal and Combustion Engineering. He then did his PhD research at Chalmers University of Technology, Gothenburg, on soot and emission formation from alternative fuels in direct injected spark ignition engines. Lars Christian is particularly expert in laser-based combustion diagnostics.
Chang Liu started in the Agile Tomography group in Edinburgh, in the role of Lecturer in Electronic Engineering, in February 2018. He carried out his PhD research at Beihang University in Beijing, on the exploitation of laser absorption spectroscopy for tomography in flames. He was a post-doctoral researcher in the EMPA laboratory at ETH Zurich, working on methods of atmospheric gas monitoring, for 2 years immediately before joining Edinburgh.
Robert Roy started at Strathclyde in the role of Post-Doctoral Researcher on the Clean Sky 2 CIDAR project, in July 2018. He obtained his MEng degree in Chemical Engineering from Strathclyde, after which he stayed on for post-graduate research on laser-induced incandescence (LII). In CIDAR, Robert is responsible for experimental and modelling work to underpin the calibration and optimise the methodology for the optical measurements of non-volatile particulate matter in aero-engine exhausts, working closely with the University of Manchester. He is particularly interested in the use of pulsed lasers for imaging of reacting flows.
Haokun Wang started as a PhD student in the Agile Tomography group in Edinburgh, in January 2019. He obtained his MSc and BEng degrees both from The University of Edinburgh. His PhD research focuses on exploiting machine learning for multiphase flow characterisation and visualisation. The aim of his research is to tackle the pressing challenge of efficient utilisation of massive, multi-modal sensing data by exploring data analytics and artificial intelligence techniques.
Yunjie Yang started in the Agile Tomography group in Edinburgh, in the role of Chancellor’s Fellow in Electronic Engineering, in October 2018. He carried out his PhD research at Edinburgh, on both technology and data inversion maths for Electrical Tomography and its applications to multiphase flow and to biological systems. He was briefly employed as a PDRA on CIDER, working on electronic testing and analysis of the FLITES data acquisition electronics. As Chancellor’s Fellow, he aims to develop further imaging techniques for biomedical applications.