Arman Ahamed Subash

Determination of reference values for optical properties of liquid phantoms based on Intralipid and India ink

A multi-center study has been set up to accurately characterize the optical properties of diffusive liquid phantoms based on Intralipid and India ink at near-infrared (NIR) wavelengths. Nine research laboratories from six countries adopting different measurement techniques, instrumental set-ups, and data analysis methods determined at their best the optical properties and relative uncertainties of diffusive dilutions prepared with common samples of the two compounds. By exploiting a suitable statistical model, comprehensive reference values at three NIR wavelengths for the intrinsic absorption coefficient of India ink and the intrinsic reduced scattering coefficient of Intralipid-20% were determined with an uncertainty of about 2% or better, depending on the wavelength considered, and 1%, respectively. Even if in this study we focused on particular batches of India ink and Intralipid, the reference values determined here represent a solid and useful starting point for preparing diffusive liquid phantoms with accurately defined optical properties. Furthermore, due to the ready availability, low cost, long-term stability and batch-to-batch reproducibility of these compounds, they provide a unique fundamental tool for the calibration and performance assessment of diffuse optical spectroscopy instrumentation intended to be used in laboratory or clinical environment. Finally, the collaborative work presented here demonstrates that the accuracy level attained in this work for optical properties of diffusive phantoms is reliable.

Broadband photon time-of-flight spectroscopy of pharmaceuticals and highly scattering plastics in the VIS and close NIR spectral ranges

We present extended spectroscopic analysis of pharmaceutical tablets in the close near infrared spectral range performed using broadband photon time-of-flight (PTOF) absorption and scattering spectra measurements. We show that the absorption spectra can be used to perform evaluation of the chemical composition of pharmaceutical tablets without need for chemo-metric calibration. The spectroscopic analysis was performed using an advanced PTOF spectrometer operating in the 650 to 1400 nm spectral range. By employing temporal stabilization of the system we achieve the high precision of 0.5% required to evaluate the concentration of tablet ingredients. In order to further illustrate the performance of the system, we present the first ever reported broadband evaluation of absorption and scattering spectra from pure and doped Spectralon®.

Spectral characterisation of dairy products using photon time-of-flight spectroscopy

In this paper, we present, for the first time, the absorption and reduced scattering spectra of commercially available milk and yoghurt products, obtained using photon-time-of-flight spectroscopy. The ability of this technique to separate the contributions from absorption and scattering in the sample provides important information on the chemical composition and micro-structural properties, which are not available with the traditional techniques used in dairy production. The instrument operates in the spectral range from 500 nm to 1030 nm. The reduced scattering coefficient varies from 5 cm−1 for milk with 0.1% fat in the near infrared range, to 60 cm−1 for yoghurt with 3.0% fat in the green wavelength regime. The absorption is within the range of 0.05–0.5cm−1, with only small variation in the absolute value between products. Our results show that the reduced scattering clearly distinguishes milk and yoghurt with the same fat content and can offer a reliable way of monitoring structural formation during milk fermentation.

Computationally effective solution of the inverse problem in time-of-flight spectroscopy

Photon time-of-flight (PTOF) spectroscopy enables the estimation of absorption and reduced scattering coefficients of turbid media by measuring the propagation time of short light pulses through turbid medium. The present investigation provides a comparison of the assessed absorption and reduced scattering coefficients from PTOF measurements of intralipid 20% and India ink-based optical phantoms covering a wide range of optical properties relevant for biological tissues and dairy products. Three different models are used to obtain the optical properties by fitting to measured temporal profiles: the Liemert-Kienle model (LKM), the diffusion model (DM) and a white Monte-Carlo (WMC) simulation-based algorithm. For the infinite space geometry, a very good agreement is found between the LKM and WMC, while the results obtained by the DM differ, indicating that the LKM can provide accurate estimation of the optical parameters beyond the limits of the diffusion approximation in a computational effective and accurate manner. This result increases the potential range of applications for PTOF spectroscopy within industrial and biomedical applications.

Flame investigation of a gas turbine central pilot body burner at atmospheric pressure conditions using oh plif and high-speed flame chemiluminescence imaging

Experiments were performed on the central pilot body (RPLrich- pilot-lean) of Siemens prototype 4th generation DLE burner to investigate the flame behavior at atmospheric pressure condition when varying equivalence ratio, residence time and co-flow temperature. The flame at the RPL burner exit was investigated applying OH planar laser-induced fluorescence (PLIF) and high-speed chemiluminescence imaging. The results from chemiluminescence imaging and OH PLIF show that the size and shape of the flame are clearly affected by the variation in operating conditions. For both preheated and non-preheated co-flow cases, at lean equivalence ratios combustion starts early inside the burner and primary combustion comes to near completion inside the burner if residence time permits. For rich conditions, the unburnt fuel escapes out through the burner exit along with primary combustion products and combustion subsequently restarts downstream the burner at leaner condition and in a diffuse-like manner. For preheated co-flow, most of the operating conditions yield similar OH PLIF distributions and the flame is stabilizing at approximately the same spatial positions. It reveals the importance of the preheating co-flow for flame stabilization. Flame instabilities were observed and Proper Orthogonal Decomposition (POD) is applied to time resolved chemiluminescence data to demonstrate how the flame is oscillating. Preheating has strong influence on the oscillation frequency. Additionally, combustion emissions were analyzed to observe the effect on NOX level for variation in operating conditions. (Less)

Numerical and Experimental Investigation of the CeCOST Swirl Burner

Clean technology has become a key feature due to increasing environmental concerns. Swirling flows, being directly associated with combustion performance and hence minimized pollutant formation, are encountered in most propulsion and power-generation combustion devices. In this study, the development process of the conceptual swirl burner developed at the Swedish National Centre for Combustion and Technology (CeCOST), is presented. Utilizing extensive computational fluid dynamics (CFD) analysis, both the lead time and cost in manufacturing of the different burner parts were significantly reduced. The performance maps bounded by the flashback and blow-off limits for the current configuration were obtained and studied in detail using advanced experimental measurements and numerical simulations. Utilizing high speed OH-chemiluminescence, OH/CH2O-PLIF and Large Eddy Simulation (LES), details of the combustion process and flame-flow interaction are presented. The main focus is on three different cases, a stable case, a case close to blow-off and flashback condition. We show the influence of the flame on the core flow and how an increase in swirl may extend the stability limit of the anchored flame in swirling flow burners. (Less)

Fuel Flexibility of a Multi-Staged Prototype Gas Turbine Burner

Gas turbines are widely used power generation equipment and very important for its efficiency and flexible operability. With the increasing demand of low carbon or less greenhouse gas emission from gas turbine, usage of clean fuel (i.e. hydrogen) is highly recommended. Adaptation with various type of fuels without any operability issues are the primary focus of interest while design and development of a low NOx gas turbine combustion system. Due to chemical and physical property variation of different fuel, a common combustion system design is complex and require extensive testing. The present paper is focused on fuel flexibility of an industrial prototype burner, designed and manufactured by Siemens Industrial Turbomachinery AB, Sweden. In this work, a baseline case (Methane fuel) is compared with different custom fuel blends (mixture of methane with natural gas and hydrogen). The primary and secondary combustion characteristics were modified when hydrogen blended fuels were introduced. The Lean Blowout limit was extended for the primary and secondary flames. The secondary flame macro structure was captured using Planar Laser Induced Fluorescence and natural luminosity imaging; whereas primary flame location was characterized by the thermocouple readings. Operational stability map and emission (NOx and CO) capability of the burner was determined from the experiment. Numerical calculation using ANSYS FLUENT was performed to simulate the combustion process and compare the results with experiment. The experimental and simulation effort provided information about the flame macrostructure and operability (lean operability limit was extended by 100 K) of the new technology burner when the combustion system was exposed to different type of fuels. (Less)

Experimental investigation of the influence of burner geometry on flame characteristics at a dry low emission industrial prototype burner at atmospheric pressure conditions

Laser based investigations were performed on a prototype 4th generation DLE (dry low emission) burner under atmospheric pressure conditions to study the effects of changing burner geometry on the flame. In a full burner configuration, a divergent conical section termed the Quarl is located after the burner exit for expanding the flow area and holding the flame. The planar laser-induced fluorescence (PLIF) of OH radicals together with the flame chemiluminescence imaging were employed to study the flame characteristics under the conditions with and without Quarl using CH4 as fuel to understand the influence of Quarl on the flame. When there is no Quarl, the flame has more freedom to expand at the burner exit and with an increase in the global equivalence ratio (φ), the width of the flame increases and the total extension of the flame shortens. For all the global φ considered here, the total extension of the flame is shorter under the condition without Quarl in comparison to the one with Quarl. For a richer global φ(φ≥ 0.46) the outer recirculation zones (ORZs) are not observed under the condition with Quarl, but are observed without Quarl along with the inner recirculation zone. Without Quarl conditions, equivalence ratios (φ) of the concentrically arranged three sections of the burner: an outer Main section, an intermediate section (Pilot) and a central pilot body or pre-chamber combustor, termed the RPL (Rich-Pilot-Lean) sections were altered. The results show that at a constant global φ, with an increase in the RPL φ and the Pilot φ, the flame shortens and expands radially as well as the flame stabilization zone that is produced after the burner exit moves further downstream. At a richer global φ, the ORZ is observed along with the inner recirculation zone of the flame. Otherwise, with an increase in global φ, the changes in the flame shape, in the flame fluctuation and in the flame stabilization position follow similar trends as for increasing the Pilot φ and the RPL φ Additionally, combustion emissions were obtained to observe the effects on NOX level for different operating conditions with and without Quarl. (Less)

Investigation of Hydrogen Enriched Methane Flame in a Dry Low Emission Industrial Prototype Burner at Atmospheric Pressure Conditions

Experiments were performed on a prototype 4th generation DLE (dry low emission) burner under atmospheric pressure conditions to investigate the effects of hydrogen (H2) enrichment on methane (CH4) flames. The burner assembly was designed to have three concentrically arranged premixed sections: an outer Main section, an intermediate section (Pilot) and a central pilot body termed the RPL (Rich-Pilot-Lean) section. The Planar laser-induced fluorescence (PLIF) of OH radicals together with flame chemiluminescence imaging were employed for studying the local flame characteristics so as to be able to investigate the turbulence-flame interactions and the location of the reaction zone at the burner exit. Flames were investigated for three different fuel mixtures having hydrogen (H2)/methane (CH4) in vol. % concentration of 0/100, 25/75 and 50/50. The results show that the characteristics of the flames are clearly affected by the addition of hydrogen and the effects are expected due to the faster reaction rate, higher diffusivity and higher laminar burning velocity of H2. Enriching the flame with H2 at a constant global phi (φ) is found to shorten the total extension of the flame due to the higher laminar flame speed. The OH signal distribution becomes thicker and more pronounced due to the higher production of OH radicals, and the flame stabilization zone that is produced after the burner throat, moves further downstream. At a constant global φ in altering the RPL and the Pilot φ, similar changes for both 0/100 and 25/75 (in vol. %) of the H2/CH4 fuel mixtures can be observed. At a rich RPL φ, the secondary RPL flame contributes to the main flame and to determining the flame stabilization position. The flame stabilization zone located after the burner throat moves further downstream with an increase in the RPL φ. When the PFR (Pilot fuel ratio) increases, the extension of the flame shortens and the flame stabilization zone moves upstream. Combustion emissions were also determined so as to observe the effects of the H2 enrichment on the NOX level. (Less)

Experimental and numerical investigation of a prototype low NOx gas turbine burner

Clean gas turbine combustion research has gained popularity in power generation and propulsion industry in recent days. Present days, advanced efficient emission (NOx, CO and UHC) reduction combustion technologies are acknowledged for using the lean premixed combustion system. To support continuous development of eco-friendly combustion system, a 4th generation dry low NOx prototype downscaled burner (designed and manufactured by Siemens Industrial Turbomachinery AB) has been researched experimentally and numerically. The research burner has multiple stages, which includes a central Pilot (named as RPL/Rich-Premixed Lean) stages, Pilot stage and Main stage. The RPL combustion chamber holds the primary flame, which produces the temperature and high concentration of radicals. The radicals and hot product is reached to the forward stagnation point of the Main flame anchoring point. Swirled reactant mixture is delivered to the Main combustion zone and a strong recirculation zone is developed. The recirculated product is moved to the Main flame root and ignites the fresh mixture. The Main flame was visualized by applying Chemiluminescence and 2D OH-PLIF imaging techniques. Emission measurement was performed to quantify the burner operability and emission competency. Burner stage fuel splits are varied and their effects on flame stability was monitored thoroughly. Computational fluid dynamic (CFD) analysis was performed to understand the flow field and compare the experimental results with numerical analysis. CFD simulation can help to identify the approximate NOx formation region and flame locations inside the burner. RPL flow and Pilot fuel split shows significant contribution towards flame stabilization as experienced from experiment and CFD. A high temperature B-type thermocouple was positioned at the liner exit to measure the exhaust gas temperature. Numerical calculation prediction and measured temperatures showed good qualitative agreement. From the present experimental and numerical research, it is evident that the downscaled prototype gas turbine burner demonstrates a wide flame stability for various operating condition. The fundamental physics behind the flame stabilization and flame dynamics were explored using numerical and experimental research. (Less)