An Experimental Study of Elliptic Turbulent Partially Premixed Propane/hydrogen/air Flames with and Without Coflow Air PDF Download
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Author: Praveen Hariharan
Publisher:
ISBN:
Category : Air flow
Languages : en
Pages : 314
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Book Description
Author: Praveen Hariharan
Publisher:
ISBN:
Category : Air flow
Languages : en
Pages : 314
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Book Description
Author:
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 432
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Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 324
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Book Description
"Education, arts and social sciences, natural and technical sciences in the United States and Canada".
Author: Frank Tat Cheong Yuen
Publisher:
ISBN: 9780494608951
Category :
Languages : en
Pages : 306
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Book Description
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.
Author: Joseph A. Wehrmeyer
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author:
Publisher:
ISBN:
Category : Power (Mechanics)
Languages : en
Pages : 786
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Author: Huahua Xiao
Publisher: Springer
ISBN: 9783662516744
Category : Technology & Engineering
Languages : en
Pages : 149
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Book Description
This thesis offers important new insights into and a deeper understanding of premixed flame instabilities and hydrogen safety. Further, it explains the underlying mechanisms that control the combustion processes in tubes. The author’s previous scientific accomplishments, which include a series of high-quality publications in the best journals in our field, Combustion and Flame and International Journal of Heat and Mass Transfer, are very impressive and have already made a significant contribution to combustion science.
Author: Vahid Vaezi
Publisher:
ISBN:
Category :
Languages : en
Pages : 310
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Author: Andrew North
Publisher:
ISBN:
Category :
Languages : en
Pages : 122
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Book Description
The carbon dioxide emission prevention advantage of generating power with high hydrogen content fuels using gas turbines motivates an improved understanding of the ignition behavior of hydrogen in premixed and partially premixed environments. Hydrogen rich fueled flame stability is sensitive to operating conditions, including environment pressure, temperature, and jet velocity. Furthermore, when premixed or partially premixed operation is desired for nitric oxide emissions reduction, a diluent, such as nitrogen, is often added in allowing fuel/air mixing prior to combustion. Thus, the concentration of the diluent added is an additional independent variable on which flame stability dependence understanding is needed. The focus of this research is on characterizing the dependence of hydrogen jet flame stability on environment temperature, jet velocity, diluent concentration, and pressure by determining the dependence of the liftoff height of lifted flames on these 4 independent parameters. Nitrogen is used as the diluent due to its availability and effectiveness in promoting liftoff. Experiments are first conducted at atmospheric pressure in scoping subsequent research where the additional parameter of pressure is added. The stability and liftoff characteristics of a nitrogen diluted hydrogen jet flame at atmospheric pressure in a vitiated co-flow are investigated experimentally and numerically with particular attention focused on regimes where multiple stabilization mechanisms are active. Information gleaned from this research is instrumental for informing modeling approaches in flame transition situations when both autoignition and flame propagation influence combustion characteristics. Stability regime diagrams which outline the conditions under which the flame is attached, lifted, blown-out, and unsteady are experimentally developed and explored. The stability of the flame is investigated with a 1D Reynolds Averaged Navier Stokes parabolic numerical model which shows that under certain conditions, local turbulent flame speeds exceed the local velocity for the production of stable lifted hydrogen flames. These modeling results suggest that the dominant flame stabilization mechanism is flame propagation, and likely tribrachial flame propagation, consistent with the conclusions of prior studies for jet flames issuing into ambient environments such as the research of Muñiz and Mungal (1997). The lifted regime is further characterized at atmospheric pressure in determining liftoff height dependence on co-flow temperature, jet velocity, and nitrogen dilution. A strong sensitivity of liftoff height to co-flow temperature, jet velocity, and nitrogen dilution is observed. The numerical model results trend well with the experimentally developed stability regime diagrams. Liftoff heights predicted by Kalghatgi's correlation are unable to capture the effects of nitrogen dilution on liftoff height for the heated co-flow cases. A uniquely formulated Damköhler number was therefore developed which acceptably captures the effects of jet velocity, nitrogen dilution and environment temperature on liftoff height. Satisfactory agreement between the correlation results which relies on propagation parameters in its formulation further indicates that stabilization is indeed dominated by propagation. The unsteady regime is also investigated experimentally at atmospheric pressure. The unsteady regime is characterized by rapid ignition events of an initially unburned jet of fuel, and these events are always followed by subsequent blowout events. The frequency by which these ignition events occur are measured and insights are drawn regarding the impact of nitrogen dilution, jet velocity, and co-flow equivalence ratio on ignition frequency. Nitrogen addition to the fuel increases autoignition delay times which reduces ignition frequency, though it also reduces the speed of flame propagation which increases the frequency of blowoff. Consequently, when the level of nitrogen dilution added to the fuel is moderate, increases in dilution increase ignition frequency, and when high levels of nitrogen are added, further increases reduce ignition frequency because each ignition event is preceded by a blowoff event. Jet velocity increases lead to broader ranges of nitrogen dilution where unsteady behavior is observed. Finally, increases in co-flow equivalence ratio result in unsteady behavior for greater levels of nitrogen dilution Experiments are also conducted at elevated pressure with co-flow temperature, jet velocity, and nitrogen dilution still parameterized. Strong sensitivity of liftoff height on co-flow temperature and pressure is observed both when jet velocity and jet Reynolds number are held constant as pressure is varied. With confinement, which is required in achieving elevated pressure, liftoff height sensitivity on jet velocity is diminished. The Damköhler number is again utilized in assessing its utility in incorporating the pressure effect, and satisfactory correlation results are demonstrated. Elevated pressure results and atmospheric pressure results (without confinement) indicate that the Damköhler number can be used in scoping experimental lifted flame research at elevated pressures and temperatures and in informing numerical modeling approaches for research as well as in industry.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 108
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Book Description
The properties of turbulent premixed flames were investigated both theoretically and experimentally. Attention was limited to hydrogen/air mixtures burning as either turbulent jet flames or a freely propagating flames in isotropic turbulence. The research has application to a variety to premixed turbulent combustion processes: underwater metal cutting at great depth, primary combustors for high-speed airbreathing propulsion systems, afterburners, fuel/ air explosions, and spark-ignition internal combustion engines. Major findings of this phase of the investigation are as follows: (1) effects of preferential diffusion are relevent for flames at high Reynolds number, retarding and enhancing the distortion of the flame surface by turbulence for stable and unstable conditions, respectively; (2) local turbulent burning velocity, flame brush thickness and the fractal dimension of the flame surface all increase with distance from the flameholder, with larger rates of increases at larger turbulence intensities; (3) estimates of flame properties using contemporary turbulence models were only fair because these methods cannot account for effects of preferential diffusion, distance from the flameholder and finite laminar flame speeds; and (4) the stochastic simulation duplicated measured trends of flame surface properties for neutral preferential diffusion conditions (the only case considered) but underestimated effects of turbulence (particularly near the flame tip) due to the limitations of a two-dimensional simulation.
