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Title: Extinction and near-extinction instability of non-premixed tubular flames

Abstract

Tubular non-premixed flames are formed by an opposed tubular burner, a new tool to study the effects of curvature on extinction and flame instability of non-premixed flames. Extinction of the opposed tubular flames generated by burning diluted H{sub 2}, CH{sub 4} or C{sub 3}H{sub 8} with air is investigated for both concave and convex curvature. To examine the effects of curvature on extinction, the critical fuel dilution ratios at extinction are measured at various stretch rates, initial mixture strengths and flame curvature for fuels diluted in N{sub 2}, He, Ar or CO{sub 2}. In addition, the onset conditions of the cellular instability are mapped as a function of stretch rates, initial mixture strengths, and flame curvature. For fuel mixtures with Lewis numbers much less than unity, such as H{sub 2}/N{sub 2}, concave flame curvature towards the fuel suppresses cellular instabilities. (author)

Authors:
; ;  [1]
  1. Mechanical Engineering Department, Vanderbilt University, Nashville, TN 37235 (United States)
Publication Date:
OSTI Identifier:
21227377
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 156; Journal Issue: 1; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; METHANE; PROPANE; FLAMES; HYDROGEN; MIXTURES; CARBON DIOXIDE; INSTABILITY; AIR; FLAME EXTINCTION; BURNERS; DILUTION; NITROGEN; HELIUM; ARGON; TUBES

Citation Formats

Hu, Shengteng, Pitz, Robert W., and Yu, Wang. Extinction and near-extinction instability of non-premixed tubular flames. United States: N. p., 2009. Web. doi:10.1016/J.COMBUSTFLAME.2008.09.004.
Hu, Shengteng, Pitz, Robert W., & Yu, Wang. Extinction and near-extinction instability of non-premixed tubular flames. United States. doi:10.1016/J.COMBUSTFLAME.2008.09.004.
Hu, Shengteng, Pitz, Robert W., and Yu, Wang. Thu . "Extinction and near-extinction instability of non-premixed tubular flames". United States. doi:10.1016/J.COMBUSTFLAME.2008.09.004.
@article{osti_21227377,
title = {Extinction and near-extinction instability of non-premixed tubular flames},
author = {Hu, Shengteng and Pitz, Robert W. and Yu, Wang},
abstractNote = {Tubular non-premixed flames are formed by an opposed tubular burner, a new tool to study the effects of curvature on extinction and flame instability of non-premixed flames. Extinction of the opposed tubular flames generated by burning diluted H{sub 2}, CH{sub 4} or C{sub 3}H{sub 8} with air is investigated for both concave and convex curvature. To examine the effects of curvature on extinction, the critical fuel dilution ratios at extinction are measured at various stretch rates, initial mixture strengths and flame curvature for fuels diluted in N{sub 2}, He, Ar or CO{sub 2}. In addition, the onset conditions of the cellular instability are mapped as a function of stretch rates, initial mixture strengths, and flame curvature. For fuel mixtures with Lewis numbers much less than unity, such as H{sub 2}/N{sub 2}, concave flame curvature towards the fuel suppresses cellular instabilities. (author)},
doi = {10.1016/J.COMBUSTFLAME.2008.09.004},
journal = {Combustion and Flame},
number = 1,
volume = 156,
place = {United States},
year = {Thu Jan 15 00:00:00 EST 2009},
month = {Thu Jan 15 00:00:00 EST 2009}
}
  • Spontaneous Raman/Rayleigh measurements have been carried out in turbulent partially premixed flames of nitrogen-diluted methane near extinction. The flames are created in a reverse flow reactor (RFR) and are stabilized by means of a recirculation zone. The flames are stretched by reducing the residence time of the flow within the reactor. The mean profiles, scatter plots, and conditional pdfs are used to study the flame structure in the present investigation. The detailed structure studies have been carried out in two shear layers, where the stretch rates are highest. The data presented in this article are for two flames close tomore » extinction at low residence times (3.6 and 5.1 ms). The flame structure at both shear layers shows quite significant chemical kinetic effects on approaching extinction. These effects reduce the products concentration and temperature and increase the reactants. Also, these effects increase the CO concentration. A substantial decrease in the reactedness of the reactive scalars has also been found at both shear layers on approaching extinction. The flame structure shows broad distribution between the equilibrium and frozen limits with no obvious bimodality. From the conditional pdfs, the reactedness decreases around stoichiometric and increases at the lean side of the stoichiometric.« less
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  • Two confined lean non-premixed swirl-stabilized flame typologies were investigated in order to achieve detailed information on the thermal and aerodynamic field in the close vicinity of the burner throat and provide correlation with the exhaust emissions. Previous finding indicated the generation of a partially premixed flame with radial fuel injection and a purely diffusive flame with co-axial injection in a swirling co-flow. In the present work, the experimental study is reported which has been conducted on a straight exit laboratory burner with no quarl cone, fuelled by natural gas and air, and fired vertically upwards with the flame stabilized atmore » the end of two concentric pipes with the annulus supplying swirled air and the central pipe delivering the fuel. Two fuel injection typologies, co-axial and radial (i.e., transverse), leading to different mixing mechanisms, have been characterized through different techniques: particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) for a comprehensive analysis of the velocity field, still photography for the detection of flame front and main visible features, and thermocouples for the temperature distribution. Isothermal flow conditions have been included in the experimental investigation to provide a basic picture of the flow field and to comprehend the modifications induced by the combustion process. The results indicated that, although the global mixing process and the main flame structure are governed by the swirl motion imparted to the air stream, the two different fuel injection methodologies play an important role on mixture formation and flame stabilization in the primary mixing zone. Particularly, it has been found that, in case of axial injection, the turbulent interaction between the central fuel jet and the backflow generated by the swirl can induce an intermittent fuel penetration in the recirculated hot products and the formation of a central sooting luminous plume, a phenomenon totally absent in the case of radial injection. (author)« less