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Author : Sunil Kumar Omar
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (179 download)
Download or read book Investigation of Turbulent Flame Characteristics Via Laser Induced Fluorescence written by Sunil Kumar Omar and published by . This book was released on 2006 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Jorrit Ernst de Vries
Publisher :
ISBN 13 :
Total Pages : 264 pages
Book Rating : 4.:/5 (257 download)
Download or read book Study on Turbulent Fluctuations in Diffusion Flames Using Laser Induced Fluorescence written by Jorrit Ernst de Vries and published by . This book was released on 1994 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Stanislav Kostka
Publisher :
ISBN 13 :
Total Pages : 532 pages
Book Rating : 4.:/5 (449 download)
Download or read book Experimental Study of Laminar and Turbulent Flame Stabilization Using Laser Diagnostics written by Stanislav Kostka and published by . This book was released on 2009 with total page 532 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Esen Cintosun
Publisher :
ISBN 13 : 9780494160541
Total Pages : 182 pages
Book Rating : 4.1/5 (65 download)
Download or read book Analysis of Premixed Turbulent Flame Front Images Obtained by Mie Scattering and Laser-induced Fluorescence of Hydroxyl Radicals written by Esen Cintosun and published by . This book was released on 2006 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt: The fractal properties, i.e., fractal dimension, and inner and outer cutoffs, of premixed turbulent flames are reported by several investigators. A comparison of the measured fractal dimension data as a function of turbulence intensity show that there are significant discrepancies among the reported results. The primary aim of the work reported here is to re-evaluate the fractal properties of the previously obtained flame front images using four different fractal analysis algorithms. In addition, perimeter ratios and flame thicknesses of flame fronts were calculated and their implications in the context of the flamelet model were discussed. These images had been obtained using experimental techniques of laser-induced fluorescence of OH, and Mie scattering on two Bunsen-type burners with diameters of 11.2 mm and 22.4 mm. For the non-dimensional turbulence intensity range of 0.84
Author : Bikram Roy Chowdhury
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (119 download)
Download or read book Experimental Investigation on the Effects of Free Stream Turbulence and Fuel Type on Structure and Blowoff Characteristics of Turbulent Premixed Bluff-body Stabilized Flames written by Bikram Roy Chowdhury and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental investigation on the effect of different levels of turbulence intensity and properties of the fuel/air mixture on the structure and characteristics of lean flames stabilized on an axisymmetric bluff body is described in this thesis. Simultaneous imaging of hydroxyl (OH) and formaldehyde (CH2O) by planar laser induced fluorescence and particle image velocimetry (PIV) were used to study the interaction between the flame and the flow field. CH2O fluorescence and the pixel-by-pixel multiplication of OH and CH2O fluorescence signals were utilized to mark preheat and heat release regions respectively. In addition, high-speed chemiluminescence imaging was performed to understand the time resolved characteristics of the flame. The first part of the thesis focuses on the characteristics of stably burning lean methane/-, propane/- and ethylene/air flames when subjected to low (4 %), moderate (14 %) and intense (24 and 30%) levels of free stream turbulence. The flame front structure was observed to be strongly dependent on the free stream turbulence level of the incoming fuel/air mixture as well on the properties of the fuel/air mixture. Formation of cusps and unburnt mixture fingers were observed as the turbulence intensity was increased from 4 to 14 % but, the heat release region remained continuous. Under intense turbulence conditions, methane/- and ethylene/air (f = 0.85) flames exhibited localized extinctions along the flame sheet and flamelet merging events which created isolated pockets of reactants in the flame envelope. In addition to these features, propane/- and ethylene/air (f=0.655) flames exhibited the occurrence of flame fragmentation events and the general shape of these flames were observed to intermittently switch from a symmetric (varicose) to asymmetric (sinuous) mode. Several properties were measured to characterize the effects of turbulence – flame interaction which includes the average preheat and reaction zone thicknesses, strain rates and curvature along the flame front, burning fraction, flame brush thickness, flame surface density, area ratio and turbulent flame speed. The next part of the thesis focuses on blowoff dynamics of lean methane/-, propane/- and ethylene/air flames for mean velocities of 5, 10 and 15 m/s and subjected to free stream turbulence levels from 4 to 30%. Apart from the propane/air flames at an apporach velcoity of 5 m/s and turbulence intensity of 30 %, increasing turbulence intensity was found to reduce the flame stability. The blowoff equivalence ratios of propane/air flames was observed to be higher than methane/- and ethylene/air flames. As blowoff was approached, the flame front and shear layer vortices entangled inducing high local strain rates on the flame front that exceed the extinction strain rate resulting in significant breaks along the reaction zone. At conditions near blowoff, significant increase in the frequency of breaks along the reaction zone was observed for low and moderate turbulence conditions. For the higher turbulence conditions, fragmentation of the flame along with the presence of sinuous wakes was observed which aided in the penetration of reactants into the recirculation zone. Velocity vectors near the flame holes indicate the penetration of the reactants into the recirculation zone. Mostly similar sequence of events was observed for methane/-, propane/- and ethylene/air flames near blowoff. Several properties weremeasured to characterize the near blowoff flames which include the strain rate and curvature statistics along the flame front, burning fraction, asymmetric index and the average duration of the blowoff event. Based on the observation from the experiments, turbulent flame speed was attributed to be the primary factor in governing the blowoff equivalence ratio. This point of view was examined by comparing the mean strain rate of methane/- and ethylene/air flames at the equivalence ratio corresponding to near blowoff for propane/air flames.
Author : Nedunchezhian Swaminathan
Publisher : Cambridge University Press
ISBN 13 : 1139498584
Total Pages : 447 pages
Book Rating : 4.1/5 (394 download)
Download or read book Turbulent Premixed Flames written by Nedunchezhian Swaminathan and published by Cambridge University Press. This book was released on 2011-04-25 with total page 447 pages. Available in PDF, EPUB and Kindle. Book excerpt: A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.
Author : Arturo Acosta-Zamora
Publisher :
ISBN 13 :
Total Pages : 91 pages
Book Rating : 4.:/5 (1 download)
Download or read book Flame Front Structures Studies of Highly Turbulent Reacting Flow Over a Backward Facing Step Using KHz OH-CH Planar Laser Induced Fluorescence written by Arturo Acosta-Zamora and published by . This book was released on 2016 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Ankit Tyagi
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (113 download)
Download or read book Dynamics of Interacting Turbulent Flames written by Ankit Tyagi and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation investigates the physics of interactions between turbulent premixed flames. It is known that multiple flame configurations provide better stability characteristics compared to a large single-flame. However, the advantages of multiple flames are limited by flame proximity as flame-flame interactions tend to reduce the burning efficiency of the reactant gases. Previous studies have shown that interactions between multiple flames directly impact the flame structure and its propagation, resulting in reduced burning efficiency. Previous experimental studies of interacting flames addressed flame-flame interactions investigating their effects on combustor stability and efficiency from a global perspective. However, the local flame-flame interaction physics was not addressed comprehensively, in part because these studies were limited to specific flow and flame configurations. In particular, these studies focused on swirling flames in bluff-body configurations typical of modern combustor geometries. Furthermore, these studies lacked flowfield measurements and were limited to flame structure and heat release rate measurements due to the complex nature of the experimental configurations. Much of the work to date on understanding the local physics of interactions comes from direct numerical simulations (DNS), but these studies treated idealized configurations of limited practical utility.To bridge these two gaps, an experimental investigation of flame-flame interactions was performed using a dual-burner rig, composed of two flames, built to facilitate precise variations in flame spacing. This rig was designed to operate in different configurations. These facilitated the focus on local interaction physics. In particular, the rig was built to study interacting V-flames and Bunsen flames. Moreover, the design of the dual-burners permitted conducting studies of nonreacting flow interactions with flames to better understand local physics of the flame. Direct flame and flow measurements were performed to characterize the mutual interaction of flame and the local flowfield. In particular, flame structure and flow were characterized using synchronized OH-planar laser-induced fluorescence (OH-PLIF) and stereoscopic-particle image velocimetry (s-PIV). These measurements were performed at a sampling rate of 10 kHz to obtain converged statistics on flame-flame interactions. A novel image processing technique was implemented for robust detection and characterization of flame-flame interaction events from OH-PLIF images.Using this experimental approach, the following studies were conducted: i) effects of flame spacing on flame structure of interacting V-flames, ii) effects of multiple flames on frequency, topology, and orientation of local flame-flame interactions, iii) effects of high mean-shear flow on flame-flame interactions, and iv) effects of pocket formation on flame dynamics. In the first study, flame spacing variations in V-flames were found to directly impact flame attachment. For smaller flame spacings, recirculation of hot combustion products near the bluff-bodies facilitated a secondary flame branch attachment in the shear layers in the interaction regions. For larger flame spacing, the secondary attachment became intermittent, indicating that closer flame spacing resulted in better attachment and stability characteristics for these flames. In the second study, the presence of adjacent flames was found to directly impact the frequencies of flame-flame interaction events. Dual-flames showed lower reactant-side interactions rates and higher product-side interactions rates when compared with single-flames. For dual-flames, comparisons between interaction orientation and local strain rate orientation showed that compressive forces led to flame front merging or pinch-off. The third study, which focused on how mean shear affects the local flame dynamics, found that high-mean shear flows entrained the flame away from the center of the burner. This entrainment directly reduced interaction event frequencies along the flame branch closest to the high mean-shear flow, while interaction event frequency in the other branch increased. Finally, flame pocket formation was investigated and results showed that a majority of the reactant pockets burned-out, while a majority of the product pockets merged with the flame surface. These results suggested that pocket behavior in turbulent flames can change local flame dynamics and it is important to capture these effects to accurately predict flame behavior. Additionally, limitations of planar high-speed imaging techniques were explored and a statistical framework, using probabilistic models, was presented in the context of reactant pocket propagation. The outcome of this work provided improved uncertainty estimation for planar measurements in three-dimensional flows.This experimental investigation provided deeper insights into the local physics of flame-flame interactions, in practical configurations, using detailed flame and flow measurements. The presence of adjacent flames influenced the attachment characteristics and local flame structure that directly impacted the stability of these multiple flame configurations. Local compressive forces facilitated the occurrence of these events, highlighting the importance of changes to the flowfield due to adjacent flames. Pocket formation, which directly affected reactant gas burning efficiency, was found to occur frequently. Taken together, these results provided comprehensive insights into the effects of flame-flame interactions that enhance our understanding of the nature of interacting flames.
Author : Jaclyn Dunn
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (141 download)
Download or read book Investigation of Premixed Sooting Flames by Combined Laser Induced Incandescence and Laser Induced Fluorescence written by Jaclyn Dunn and published by . This book was released on 2013 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study applies the techniques of laser induced incandescence (LII) and laser induced fluorescence (LIF) to investigate laminar sooting flames of premixed ethylene air. The approach involves using three different excitation wavelengths, together with temporally and spectrally resolved detection, generating a rich dataset concerning the formation of soot and polycyclic aromatic hydrocarbons (PAHs). Both prompt and delayed detection are used to perform LII when exciting with short wavelengths, both with issues involved. Delayed detection gives an underestimation of soot volume fraction at low heights in the flame, as a result of particle size effects. Prompt detection gives overestimation of soot volume fraction due to fluorescence in the measurement volume. It is shown that care must be taken with either method and through evaluation of the associated errors this study shows delayed detection provides a more accurate measure of soot volume fraction. The ability to obtain the fluorescence signals over a range of heights above burner and stoichiometries is demonstrated. The approach relies on heating the soot particles equivalently with three excitation wavelengths so the LII contribution to the signals can be subtracted, leaving only fluorescence. Fluorescence profiles obtained show similar features to those seen in the literature for invasive measurements, including a reduction in the fluorescence signal generated by 283 nm excitation at intermediate heights above the burner surface followed by a re-increase. Although the data do not allow species-selective measurements of PAHs, these in-situ measurements allow inferences to be drawn about changing concentration of different size classes of these precursors to soot formation. Finally the method of obtaining subtracting the LII contribution to signals was used to obtain fluorescence spectra both for 283 nm and 532 nm excitation. This showed the possibility that fluorescence can yield useful information that it is otherwise impossible to obtain in-situ under sooting conditions.
Author : Robin Simon Macpherson Chrystie
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (879 download)
Download or read book Development of Novel Laser Diagnostic Techniques for the Quantitative Study of Premixed Flames written by Robin Simon Macpherson Chrystie and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The main topic of this thesis concerns the development and application of laser diagnostic techniques for accurate temperature measurements and for the determination of flamefront properties in premixed flames that can serve as input data for computational fluid dynamical (CFD) models in technical combustion. The work comprises of a number of related studies, to address problems of relevance in the field of combustion research. The first part of this work involves the development and testing of an improved method for the computation of flamefront curvature in lean premixed turbulent flames. Measurements of spatially resolved heat release rate along the flamefront were then compared with the curvature data and it could be shown that a significant correlation exists between local rate of heat release and flamefront curvature. The results here agree with predictions from CFD models and improve on previous experimental attempts to find a correlation between curvature and heat release. In the second part of this work, the focus was shifted towards the development and application of improved thermometry techniques. One study was on the improvement and application of a coherent anti-Stokes Raman spectroscopy (CARS) setup to an acoustically-forced turbulent lean premixed flame stabilised on a burner, whose design was modelled to mimic phenomena of relevance in industrial combustors. In a related previous study reported in the literature two-line OH planar laser induced fluorescence had been applied to this flame and it was suspected that the results were inaccurate. Using CARS, these inaccuracies could be verified, amounting to discrepancies in temperature of up to 47% compared to the true temperatures. A major effort towards the end of this project was focused on the improvement of traditional thermometry techniques, in order to make them more accurate, faster, and spatially resolved. A technique based on indium two-line atomic fluorescence (TLAF) thermometry was developed and applied, which employed a novel extended cavity diode laser design, and it was shown for the first time that temperature measurements with high accuracy and precision could be performed in low pressure sooting flames without recourse to calibration. Both the high precision and accuracy of the technique allowed for the deduction that the temperature in the flames studied here is relatively insensitive to changes in pressure in stark contrast to the soot volume fraction. Finally, it is shown for the first time that low power diode lasers can be used in combination with indium TLAF to measure spatially and temporally highly resolved temperatures in a quasi-continuous fashion. We demonstrated such measurements at effective rates of 3.5 kHz in a steady laminar test flame yielding an unprecedented precision of 1.5 % at ~2000 K at this measurement rate.
Author :
Publisher :
ISBN 13 :
Total Pages : 26 pages
Book Rating : 4.:/5 (227 download)
Download or read book Rapid Concentration Measurements by Picosecond Time-Resolved Laser-Induced Fluorescence written by and published by . This book was released on 1998 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantitative measurements of scalars in combustion are crucial to our understanding of flame structure and pollutant production. Progress has been made in quantitatively characterizing many laminar flames; however, the inherent fluctuations in turbulent flames significantly complicate such measurements. Picosecond time-resolved laser-induced fluorescence (PITLIF) is a developing technique which seeks to provide the first known means of obtaining quantitative minor-species concentrations in flames at rates sufficient for the study of turbulent fluctuations. This method was developed and applied to measurements of sodium and OH concentrations in laminar flames under previous AFOSR funding. The present report details the construction of a second generation PITLIF instrument. The primary goal of this work is to provide a continuous time series of quantitative concentrations from which frequency domain statistics such as the power spectral density (PSD) can be computed. Using the new laser system, fluorescence measurements of CH and OH time series were collected in a variety of methane and hydrogen flames including nonpremixed turbulent flames. These data have also been compared with available velocity and temperature measurements. The time series and resulting PSDs represent the first measurements of these statistics for minor-species concentrations.
Author : Nasa Technical Reports Server (Ntrs)
Publisher : BiblioGov
ISBN 13 : 9781289167400
Total Pages : 24 pages
Book Rating : 4.1/5 (674 download)
Download or read book Oh Planar Laser Induced Fluorescence Measurements for the Study of High Pressure Flames written by Nasa Technical Reports Server (Ntrs) and published by BiblioGov. This book was released on 2013-07 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: Planar laser induced fluorescence (PLIF) is used by the Combustion Branch at the NASA Glenn Research Center (NASA Glenn) to assess the characteristics of the flowfield produced by aircraft fuel injectors. To improve and expand the capabilities of the PLIF system new equipment was installed. The new capabilities of the modified PLIF system are assessed by collecting OH PLIF in a methane/air flame produced by a flat flame burner. Specifically, the modifications characterized are the addition of an injection seeder to a Nd: YAG laser pumping an optical parametric oscillator (OPO) and the use of a new camera with an interline CCD. OH fluorescence results using the injection seeded OPO laser are compared to results using a Nd: YAG pumped dye laser with ultraviolet extender (UVX). Best settings of the new camera for maximum detection of PLIF signal are reported for the controller gain and microchannel plate (MCP) bracket pulsing. Results are also reported from tests of the Dual Image Feature (DIF) mode of the new camera which allows image pairs to be acquired in rapid succession. This allows acquisition of a PLIF image and a background signal almost simultaneously. Saturation effects in the new camera were also investigated and are reporte
Author :
Publisher :
ISBN 13 :
Total Pages : 23 pages
Book Rating : 4.:/5 (227 download)
Download or read book Measured Properties of Turbulent Premixed Flames for Model Assessment, Including Burning Velocities, Stretch Rates, and Surface Densities (Postprint). written by and published by . This book was released on 2006 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: One goal of this work was to quantify several properties of turbulent premixed flames that have not been quantified before and are especially useful for the assessment of direct numerical simulations (DNS) and models. It was decided to select a flame that is in the corrugated flamelet regime and use simultaneous CH planar laser-induced fluorescence/ particle image velocimetry (CH PLIF/PIV) diagnostics, which previously had been applied only to nonpremixed combustion. These diagnostics allow one to identify the thin wrinkled reaction zone (where CH exists) and the nearby velocity field. Properties that were measured include local stretch rates, a wrinkling parameter, the degree of flamelet extinction, reaction layer thicknesses, flame surface density (), and global consumption speed, which is one type of turbulent burning velocity that is described below.
Author : Seung Hyuck Hong
Publisher :
ISBN 13 :
Total Pages : 216 pages
Book Rating : 4.:/5 (897 download)
Download or read book Towards Predicting Dynamics in Turbulent Premixed Combustion Using PIV-PLIF Measurements of Flow-flame Microstructure written by Seung Hyuck Hong and published by . This book was released on 2014 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt: Combustion dynamics are critical to the development of high-efficiency, low-emission and fuel-flexible combustion systems used for propulsion and power generation. Predicting the onset of dynamics remains a challenge because of the complex interactions among several multi-scale phenomena, including turbulence, kinetics and acoustics, and their strong dependence on the operating conditions and fuel properties. In this thesis, a series of experiments were conducted in a laboratory-scale combustor, burning lean premixed propane/hydrogen/air mixtures over a range of equivalence ratio, fuel composition and inlet temperature. Dynamic pressure and flame chemiluminescence measurements are used to determine macro-scale characteristics such as the frequency, limit cycle amplitude and dynamic flame shape. High-speed, high-resolution particle image velocimetry (PIV) is used to quantify the micro-scale structure of the flow, while planar laser-induced fluorescence (PLIF) of OH radical is used to investigate the flame microstructure. Results demonstrate that combustion dynamics in wake-stabilized flames can be characterized using a single non-dimensional parameter that collapses many response measures over a range of operating conditions and fuel composition, including the critical wake length at which dynamics is first observed, the critical phase at which transition among dynamic modes is encountered, and the limit cycle amplitude, emphasizing the role of the physics and chemistry of the flame processes in driving the overall system dynamics and encapsulating the governing mechanisms. The proposed parameter is based on the normalized strained flame consumption speed, which encapsulates the flow-combustion interactions at the flame scale. PIV data reveal significant changes in the recirculation zone structure depending on the equivalence ratio and the fuel composition, demonstrating the impact of chemical kinetics on the flow. These changes are shown to correlate strongly with the stability characteristics, i.e., blow-off and flashback limits as well as the onset of the thermoacoustic instabilities, highlighting a critical role of the recirculation zone in flame stabilization. An expression for the critical phase at which dynamic mode transition occurs is derived based on the linear acoustic energy balance. It is shown that the critical phase is also a function of the same non-dimensional parameter, suggesting that it represents the state within a dynamic mode as well. Results show that the normalized phase correlates with the upper- and lower-boundary of a dynamic mode, thus being a necessary and sufficient condition for dynamics. The results provide a metric for quantifying the instability margins of fuel-flexible combustors operating over a wide range of conditions. Analysis of PIV and OH-LIF data suggests that heat transfer near the flame-holder may play an important role in determining the stability characteristics. The impact of heat transfer on the onset of dynamics is experimentally investigated using different flame-holders. Results demonstrate the effectiveness of using heat-insulating materials as a passive control strategy to prevent or significantly delay the onset of the instabilities.
Author : National Aeronautics and Space Adm Nasa
Publisher : Independently Published
ISBN 13 : 9781794369306
Total Pages : 24 pages
Book Rating : 4.3/5 (693 download)
Download or read book Oh Planar Laser Induced Fluorescence (Plif) Measurements for the Study of High Pressure Flames: An Evaluation of a New Laser and a New Camera System written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2019-01-19 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: Planar laser induced fluorescence (PLIF) is used by the Combustion Branch at the NASA Glenn Research Center (NASA Glenn) to assess the characteristics of the flowfield produced by aircraft fuel injectors. To improve and expand the capabilities of the PLIF system new equipment was installed. The new capabilities of the modified PLIF system are assessed by collecting OH PLIF in a methane/air flame produced by a flat flame burner. Specifically, the modifications characterized are the addition of an injection seeder to a Nd: YAG laser pumping an optical parametric oscillator (OPO) and the use of a new camera with an interline CCD. OH fluorescence results using the injection seeded OPO laser are compared to results using a Nd: YAG pumped dye laser with ultraviolet extender (UVX). Best settings of the new camera for maximum detection of PLIF signal are reported for the controller gain and microchannel plate (MCP) bracket pulsing. Results are also reported from tests of the Dual Image Feature (DIF) mode of the new camera which allows image pairs to be acquired in rapid succession. This allows acquisition of a PLIF image and a background signal almost simultaneously. Saturation effects in the new camera were also investigated and are reported. Tedder, Sarah and Hicks, Yolanda Glenn Research Center NASA/TM-2012-217614, E-182
Author : Christelle C. G. Magand
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (16 download)
Download or read book Joint Stereo-PIV and NO-LIF in Turbulent Premixed Hydrogen-air Flames written by Christelle C. G. Magand and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A new technique to simultaneously and instantaneously resolve 3D velocity/2D strain rate fields and scalar/scalar gradient fields was developed and evaluated in this study. This technique combines Planar Laser Induced Fluorescence of the NO radical (NO-PLIF) and Stereoscopic Particle Image Velocimetry (SPIV). It was found that the NO-PLIF technique allowed the determination of various iso-c contours and as such would, in principle, allow the study of the influence of the heat release on various properties, provided a calibration of the NO-PLIF signal as a function of temperature is achieved. It was also shown that the NO-PLIF technique may not be unambiguous at detecting flame extinction. The SPIV technique allowed the determination of the velocities in 3D and of the strain rates in 2D from which the most extensive and the most compressive strain rates but not the intermediate strain rate could be extracted. Information on strain rates and progress variable gradients were of particular interest in this study as they were needed to study the turbulence-scalar interaction which appears explicitly in the transport equation for the scalar dissipation rate which was derived recently. Using the technique above mentioned, this work also aimed at gathering and analysing data such as flame normal orientation, progress variable gradients, velocity change across the flame front and strain rates along the flame contours in turbulent premixed hydrogen/air flames with added nitrogen. The flame normal orientation was found to be consistent with the regime of the flames studied. A new method was designed and presented to infer from the progress variable gradients the component of the flame normal in the third dimension. The velocity change across the flame front, inferred from the SPIV data, was found to be extremely small. It is thought that the (low) heat release of the flames studied contributed more to corrugation of the flame front than acceleration of the gases across the flame front. The strain rates were studied along apparently non-wrinkled and clearly wrinkled flame contours. Their variation could not successfully be linked to curvature solely. Their values were mostly below the value expected for extinction strain rates. Last, this study aimed at investigating the turbulence-scalar interactions in turbulent premixed hydrogen/air flames with added nitrogen via the characteristics of the alignment of the flame normal vectors with the principal strain rates. The results of this study are quite different from earlier experimental results obtained for turbulent premixed ethylene/air flames. The strong preferential alignment of the flame front normal with the most extensive strain rate observed for ethylene/air flames could not be observed for the hydrogen/air flames with added nitrogen studied in the present work. The key outcome of this study was that no preferential alignment could be observed for most of the flames. A slight preferential alignment of the flame front normal with the most compressive strain rate was observed for the flames with very low adiabatic flame temperature. The differences observed were attributed partly to Lewis number effects and partly to the low heat release superimposed on the hydrodynamic fields in the flames studied.
Author : Greg R. Schneider
Publisher :
ISBN 13 :
Total Pages : 161 pages
Book Rating : 4.:/5 (227 download)
Download or read book Application of Laser-Induced Fluorescence in an Atmospheric-Pressure Boron-Seeded Flame written by Greg R. Schneider and published by . This book was released on 1987 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this research was to demonstrate the feasibility of using laser-induced fluorescence (LIF) of boron oxide radicals in atmospheric-pressure flames. Such a demonstration would provide a useful tool with which to probe the detailed combustion chemistry of boron fuels. The radical species sought were BO2 and BO, both having spectra in the visible region of the spectrum. These two species are believed to play critical roles in the boron combustion process. A CH4/air/O2 flame was seeded with BC13 producing the green emission characteristic of boron flames. Unfortunately, it also created significant quantities of aerosols of solid boric acid from the reaction of the BC13 with the water vapor in the building air used in the flame. The burner was 1 cm in diameter and composed of approximately 60 capillary tubes. The burner could be remotely translated in two directions permitting investigation of different regions of the flame.
