Download or read book Investigation of Structure and Dynamics of Turbulent Premixed and Stratified Methane air Flames Using Laser Diagnostic Techniques written by Muḥammad Muṣṭafá Kamāl and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Measurements of the Structure of Turbulent Premixed and Stratified Methane written by Mark Sweeney and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The influence of stratification on the structure of turbulent methane/air combustion is investigated using experimental data from laboratory scale burners: a weakly turbulent slot burner, and a higher turbulence co-annular swirl burner. The degree of stratification can be controlled independently of the overall fuel/air flow rate. The resulting measurements of scalar and velocity fields provide detailed test cases for existing and emerging turbulent flame models, covering a range of u'/sL from 1 to 10, turbulence intensities from 5% to 60%, and stratification ratios from 1 to 3. Simultaneous Rayleigh/Raman/CO-LIF measurements of temperature and major species concentrations - CH4, CO2, CO, H2, H2O and O2 - along a line are used to investigate the structure of a series of flames in both the slot and swirl burners. Concurrent cross-planar OH-PLIF allows thermal gradients to be angle corrected to their three-dimensional values. Finally, non-reacting and reacting velocity fields complete the flame database. The behavior of major species concentrations in the slot and swirl burner with respect to temperature is found to agree well on the mean with unstrained premixed laminar flame calculations. Scalar means conditioned on stoichiometry also show good agreement, aside from hydrogen which is enhanced under stratified conditions. Surface density function and scalar dissipation are lower than calculated values in all cases, suggesting that turbulence-induced thickening dominates the effect of increased strain. Metrics commonly used to derive flame surface density (FSD) were investigated. FSD may be determined using a statistical method based on measurements of temperature and its gradient, or a geometric method based on 2D temperature or LIF imaging. A third metric, an extension of the geometric method, is proposed. Good agreement is observed between the three metrics. The current database provides the first detailed high resolution scalar measurements for premixed and stratified flames. The data analysis provides insight into the physics of stratification: for the flames considered, the effects of stratification appear to be surprisingly small compared to those of turbulence, even at significant stratification ratios. The datasets provide a means of validating current and future computational turbulent combustion models.
Download or read book Stabilization and Dynamic of Premixed Swirling Flames written by Paul Palies and published by Academic Press. This book was released on 2020-07-03 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stabilization and Dynamic of Premixed Swirling Flames: Prevaporized, Stratified, Partially, and Fully Premixed Regimes focuses on swirling flames in various premixed modes (stratified, partially, fully, prevaporized) for the combustor, and development and design of current and future swirl-stabilized combustion systems. This includes predicting capabilities, modeling of turbulent combustion, liquid fuel modeling, and a complete overview of stabilization of these flames in aeroengines. The book also discusses the effects of the operating envelope on upstream fresh gases and the subsequent impact of flame speed, combustion, and mixing, the theoretical framework for flame stabilization, and fully lean premixed injector design. Specific attention is paid to ground gas turbine applications, and a comprehensive review of stabilization mechanisms for premixed, partially-premixed, and stratified premixed flames. The last chapter covers the design of a fully premixed injector for future jet engine applications. Features a complete view of the challenges at the intersection of swirling flame combustors, their requirements, and the physics of fluids at work Addresses the challenges of turbulent combustion modeling with numerical simulations Includes the presentation of the very latest numerical results and analyses of flashback, lean blowout, and combustion instabilities Covers the design of a fully premixed injector for future jet engine applications
Download or read book Experimental Investigation of the Dynamics and Structure of Lean premixed Turbulent Combustion written by Frank Tat Cheong Yuen and published by . This book was released on 2009 with total page 306 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent premixed propane/air and methane/air flames were studied using planar Rayleigh scattering and particle image velocimetry on a stabilized Bunsen type burner. The fuel-air equivalence ratio was varied from &phis; = 0:7 to 1.0 for propane flames, and from &phis; = 0:6 to 1.0 for methane flames. The non-dimensional turbulence intensity, u'/ SL (ratio of fluctuation velocity to laminar burning velocity), covered the range from 3 to 24, equivalent to conditions of corrugated flamelets and thin reaction zones regimes. Temperature gradients decreased with the increasing u'/SL and levelled off beyond u'/SL > 10 for both propane and methane flames. Flame front thickness increased slightly as u'/SL increased for both mixtures, although the thickness increase was more noticeable for propane flames, which meant the thermal flame front structure was being thickened. A zone of higher temperature was observed on the average temperature profile in the preheat zone of the flame front as well as some instantaneous temperature profiles at the highest u'/SL. Curvature probability density functions were similar to the Gaussian distribution at all u'/ SL for both mixtures and for all the flame sections. The mean curvature values decreased as a function of u'/ SL and approached zero. Flame front thickness was smaller when evaluated at flame front locations with zero curvature than that with curvature. Temperature gradients and FSD were larger when the flame curvature was zero. The combined thickness and FSD data suggest that the curvature effect is more dominant than that of the stretch by turbulent eddies during flame propagation. Integrated flame surface density for both propane and methane flames exhibited no dependance on u'/S L regardless of the FSD method used for evaluation. This observation implies that flame surface area may not be the dominant factor in increasing the turbulent burning velocity and the flamelet assumption may not be valid under the conditions studied. Dkappa term, the product of diffusivity evaluated at conditions studied and the flame front curvature, was a magnitude smaller than or the same magnitude as the laminar burning velocity.
Download or read book Measurements of the structure of turbulent premixed and stratified methane air flames written by Mark Sweeney and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigation of Thermal Flame Structure in Lean Turbulent Premixed Methane air Flames by Rayleigh Scattering written by Natalie Galley and published by . This book was released on 2006 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: Flame front structure in turbulent premixed methane-air and propane-air flames was investigated. Flame images were obtained using Rayleigh scattering on an axisymmetric Bunsen-type burner. Normalized turbulence intensity, u'/SL, was varied from 3.4 to 15.92 for methane-air flames, and 3.31 to 8.61 for propane-air flames. Instantaneous thermal flame thicknesses and gradients were found from normal temperature profiles. For methane-air flames, flame front thickness decreased as equivalence ratio increased and preheat zone and reaction zone thicknesses increased slightly as u'/SL increased. When normalized by laminar flame values, the thicknesses decreased. Strain was found to play an unimportant role in determining flame front thickness. Fewer than 30 profiles were found that exhibit a temperature Bump in the low temperature region of the profile, indicating that turbulent eddies convecting heated matter into the preheat zone probably do not cause the change in the preheat zone structure. For propane-air flames preliminary results are presented.
Download or read book Experimental Investigation of Stratified Combustion written by Saravanan Balusamy and published by LAP Lambert Academic Publishing. This book was released on 2012 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to better understand the stratified combustion, the propagation of flame through stratified mixture field in laminar and turbulent flow conditions has been studied by using combined PIV/PLIF techniques. A great emphasis was placed on developing methods to improve the accuracy of local measurements of flame propagation. In particular, a new PIV approach has been developed to measure the local fresh gas velocity near preheat zone of flame front. To improve the resolution of measurement, the shape of interrogation window has been continuously modified based on the local flame topology and gas expansion effect. Statistical analysis of conditioned local measurements by the local equivalence ratio of flames allows the characterization of the properties of flame propagation subjected to the mixture stratification in laminar and turbulent flows, especially the highlight of the memory effect.
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.
Download or read book Experimental Study of Turbulent Premixed Combustion in V shaped Flames written by Sina Kheirkhah and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Characteristics of turbulent premixed flames were investigated experimentally. The investigations were performed using Mie scattering, Particle Image Velocimetry, Rayleigh scattering, and broad-band luminosity imaging techniques. Methane-air flames associated with a relatively wide range of turbulence intensities, fuel-air equivalence ratios, and mean bulk flow velocities were investigated. For a relatively moderate value of turbulence intensity, a new concept is introduced and utilized to provide a detailed description associated with interaction of turbulent flow and flame front. The concept pertains to reactants velocity estimated at the vicinity of the flame front and is referred to as the edge velocity. Specifically, it is shown that fluctuations of the flame front position are induced by fluctuations of the edge velocity. For a relatively wide range of turbulence intensity, several characteristics of turbulent premixed flames, namely, front topology, brush thickness, surface density, and consumption speeds are investigated. For the first time, several flame front structures are identified and studied. It is shown that, due to formation of these front structures, the regime of turbulent premixed combustion transitions from the regime of counter-gradient diffusion to that of the gradient diffusion. In addition to these, a comprehensive study is performed to investigate influence of flame configuration on several flame front characteristics. It is obtained that, although changing the flame configuration influences several flame characteristics, the trends associated with the effects of governing parameters on the characteristics are nearly independent of the flame configuration.
Download or read book Experimental Investigation of Flow Turbulence Effects on Premixed Methane air Flames written by Kenneth Owen Smith and published by . This book was released on 1978 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Laser Diagnostics of Turbulent Flames in High Speed Flows written by Nathan Ryan Grady and published by . This book was released on 2015 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fundamental Studies of Flame Structure Through Laser Plasma Diagnostics written by Wendong Wu and published by . This book was released on 2017 with total page 175 pages. Available in PDF, EPUB and Kindle. Book excerpt: Increasing concerns about air pollution and global climate change are drawing attention to the need for efficiency improvements and emission reductions for combustion processes, which account for more than 85% of energy production in United States. Combustion efficiency and emissions are affected by the mixing and reacting of fuel and oxidizer. Understanding such behavior plays a critical role in flame structure studies and combustion optimization. However, experimentally obtaining mixture fraction, which is a widely used quantity to describe the mixing behavior, has proven to be a challenge, especially for heavier hydrocarbon fuels or fuel rich flames. Moreover, measuring flame temperature simultaneously with mixture fraction adds complexity into the experimental setup. In this dissertation, laser plasma diagnostics techniques were developed to provide a straightforward method to simultaneously obtain composition and temperature measurements. The capability of these novel techniques is applicable to more complex fuels and a broader range of equivalence ratios than has heretofore been possible, and facilitates a better understanding of flame structure.Laser-induced breakdown spectroscopy (LIBS) is proposed as an alternative method of measuring mixture fraction. A back-scattering setup is utilized to mitigate the beam steering effects in non-uniform and unsteady flames. The calibration for the LIBS system was completed in an ethylene-air premixed flame under a broad range of equivalence ratios. The elemental species distributions for H, C, N, O were measured in a counter-flow diffusion flame. The measured mixture fraction compared favorably with the numerical results from OPPDIF flame code. On the basis of LIBS measured elemental species profile, the preferential diffusion effect was analyzed.Utilizing the sound emission from laser-induced plasmas, acoustic-based laser induced breakdown thermometry (LIBT) was developed as a novel method for flame temperature measurement. The established correlation between the optical emission and acoustic emission in a premixed flame demonstrated that the acoustic signal can serve as an internal standard in the gas phase LIBS measurement. The influences of flame temperature and composition on the acoustic signal were investigated independently. The composition effect was found to be second order comparing to the temperature effect. The statistics of the LIBT measurement were also analyzed to better understand the distribution of samples. Furthermore, the temperature and gas density distributions in a counter-flow diffusion flame were measured using LIBT and were found to compare favorably with numerical results. To evaluate the possibility of simultaneous composition and temperature measurement using laser plasma diagnostics, the spatial and temporal resolutions of LIBS and LIBT were carefully examined. The accuracy of LIBT technique was analyzed as a function of sample size from a statistical perspective. The results demonstrated that LIBT has spatial and temporal resolutions comparable to that of LIBS. Finally, a preliminary study using a Burke- Schumann flame and a Hencken burner was performed to understand the influence of turbulent flow.Measuring composition and temperature simultaneously using laser plasma diagnostics provides substantial benefits over traditional measurement technique. However, in exchange for such benefits, information on major species concentrations can no longer be directly measured. To infer the molecular species profile from the elemental species profile, the underlying partial-equilibrium assumption was examined. Among partially-equilibrated reactions, the water-gas shift (WGS) reaction is most often assumed to be in equilibrium because of its important role in the high temperature zone. Thus, the equilibrium domain of WGS reaction was systematically studied in different hydrocarbon flames under varying strain rates to evaluate the validity of partial equilibrium assumption. The underlying mechanism for WGS-equilibrium was also examined. The results suggested that even though the WGS reaction has a broad partial-equilibrium domain in syngas, methane, ethylene and propane flames, the mechanisms responsible for partial equilibrium were very different. In hydrocarbon flames, the water-gas-shift reaction can achieve partial equilibrium even though the two elementary reactions behind it are not equilibrated.
Download or read book The Structure of a Turbulent Premixed Rod stabilized Methane air V flame written by Robert Linton Godown and published by . This book was released on 1987 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Correlation of Flame Speed with Stretch in Turbulent Premixed Methane air Flames written by and published by . This book was released on 1997 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the flamelet approach of turbulent premixed combustion, the flames are modeled as a wrinkled surface whose propagation speed, termed the {open_quotes}displacement speed, {close_quotes} is prescribed in terms of the local flow field and flame geometry. Theoretical studies suggest a linear relation between the flame speed and stretch for small values of stretch, S{sub L}/S{sub L}° = 1 - MaKa, where S{sub L}° is the laminar flame speed, Ka = [kappa][delta]{sub F}/S{sub L}° is the nondimensional stretch or the Karlovitz number, and Ma = L/[delta]{sub F} is the Markstein number. The nominal flame thickness, [delta]{sub F}, is determined as the ratio of the mass diffusivity of the unburnt mixture to the laminar flame speed. Thus, the turbulent flame model relies on an accurate estimate of the Markstein number in specific flame configurations. Experimental measurement of flame speed and stretch in turbulent flames, however, is extremely difficult. As a result, measurement of flame speeds under strained flow fields has been made in simpler geometries, in which the effect of flame curvature is often omitted. In this study we present results of direct numerical simulations of unsteady turbulent flames with detailed methane/air chemistry, thereby providing an alternative method of obtaining flame structure and propagation statistics. The objective is to determine the correlation between the displacement speed and stretch over a broad range of Karlovitz numbers. The observed response of the displacement speed is then interpreted in terms of local tangential strain rate and curvature effects. 13 refs., 3 figs.
Download or read book Velocity and Scalar Measurements in Turbulent Premixed and Stratified Methane air Flames written by Ruigang Zhou and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1992 with total page 1556 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Investigations of Turbulent Stratified V flames Using Laser Diagnostics written by Pedro Anselmo Filho and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
