Transitions and blowoff of unconfined non-premixed swirling flame

The present experimental work reports the first observations of primary and secondary transitions in the time-averaged flame topology in a non-premixed swirling flame as the geometric swirl number S-G (a non dimensional number used to quantify the intensity of imparted swirl) is varied from a magnitude of zero till flame blowout. First observations of two transition types viz. primary and secondary transitions are reported. The primary transition represents a transformation from yellow straight jet flame (at S-G = 0) to lifted flame with blue base and finally to swirling seated (burner attached) yellow flame. Time-averaged streamline plot obtained from 2D PIV in mid-longitudinal plane shows a recirculation zone (RZ) at the immediate vicinity of burner exit. The lifted flame is stabilized along the vortex core of this RZ. Further, when S-G similar to 1.4-3, the first occurrence of vortex breakdown (VB) induced internal recirculation zone (IRZ) is witnessed. The flame now stabilizes at the upstream stagnation point of the VB-IRZ, which is attached to the burner lip. The secondary transition represents a transformation from a swirling seated flame to swirling flame with a conical tailpiece and finally to a highly-swirled near blowout oxidizer-rich flame. This transition is understood to be the result of transition in vortex breakdown modes of the swirling flow field from dual-ring VB bubble to central toroidal recirculation zone (CTRZ). The physics of transition is described on the basis of modified Rossby number (Ro(m)). Finally, when the swirl intensity is very high i.e. SG similar to 10, the flame blows out due to excessive straining and due to entrainment of large amount of oxidizer due to partial premixing. The present investigation involving changes in flame topology is immensely important because any change in global flame structure causes oscillatory heat release that can couple with dynamic pressure and velocity fluctuations leading to unsteady combustion. In this light, understanding mechanisms of flame stabilization is essential to tackle the problem of thermo-acoustic instability. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

[1]  Y. Yoon,et al.  EINOx scaling in a non-premixed turbulent hydrogen jet with swirled coaxial air , 2010 .

[2]  Tim Lieuwen,et al.  Recirculation zone dynamics of a transversely excited swirl flow and flame , 2012 .

[3]  A. Melling.  Tracer particles and seeding for particle image velocimetry , 1997 .

[4]  S. Plee,et al.  Characteristic time correlation for lean blowoff of bluff-body-stabilized flames☆ , 1979 .

[5]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[6]  Jeongseog Oh,et al.  The effect of fuel composition on the characteristics of a non-premixed synthetic natural gas-air flame , 2014 .

[7]  A. Lefebvre,et al.  Flame blowoff studies using large-scale flameholders , 1982 .

[8]  Renwei Mei,et al.  Flow due to an oscillating sphere and an expression for unsteady drag on the sphere at finite Reynolds number , 1994, Journal of Fluid Mechanics.

[9]  V. Yang,et al.  Unsteady flow evolution in swirl injector with radial entry. I. Stationary conditions , 2005 .

[10]  D. Feikema,et al.  Blowout of nonpremixed flames: Maximum coaxial air velocities achievable, with and without swirl☆ , 1991 .

[11]  Tim Lieuwen,et al.  Acoustic Detection of Blowout in Premixed Flames , 2005 .

[12]  On the stability of a turbulent non-premixed biogas flame: Effect of low swirl strength , 2014 .

[13]  Y. Yoon,et al.  Acoustic excitation effect on NOx reduction and flame stability in a lifted non-premixed turbulent hydrogen jet with coaxial air , 2009 .

[14]  D. Banerjee,et al.  On Flame Stabilization by Bluff-Bodies , 1980 .

[15]  T. Lieuwen,et al.  Flame Leading Edge and Flow Dynamics in a Swirling, Lifted Flame , 2012 .

[16]  M. Q. McQuay,et al.  Systematic measurements of OH chemiluminescence for fuel-lean, high-pressure, premixed, laminar flames , 2001 .

[17]  J. Lee,et al.  The Dynamic Response of Turbulent Dihedral V Flames: An Amplification Mechanism of Swirling Flames , 2010 .

[18]  D. Ballal,et al.  Aerodynamics of Bluff-Body Stabilized Confined Turbulent Premixed Flames , 1992 .

[19]  T. Hasegawa,et al.  Structure and blow-off mechanism of rod-stabilized premixed flame , 1985 .

[20]  T. Lieuwen,et al.  Flame and Flow Topologies in an Annular Swirling Flow , 2014 .

[21]  B. Cetegen,et al.  Blowoff mechanism of two dimensional bluff-body stabilized turbulent premixed flames in a prototypical combustor , 2011 .

[22]  G. S. Samuelsen,et al.  Scaling and development of low-swirl burners for low-emission furnaces and boilers , 2000 .

[23]  K. Hanjalić,et al.  Hysteresis and transition in swirling nonpremixed flames , 2009 .

[24]  Tim Lieuwen,et al.  Near-Blowoff Dynamics of a Bluff-Body Stabilized Flame , 2007 .

[25]  W. Sharpe.  Springer Handbook of Experimental Solid Mechanics , 2008 .

[26]  Muruganandam Thiruchengode,et al.  Sensing and Dynamics of Lean Blowout in a Swirl Dump Combustor , 2006 .

[27]  Suraj Nair.  Acoustic Characterization of Flame Blowout Phenomenon , 2006 .

[28]  B. Cetegen,et al.  Blowoff dynamics of bluff body stabilized turbulent premixed flames , 2010 .

[29]  Viswanath R. Katta,et al.  Study of flame stability in a step swirl combustor , 1996 .

[30]  E. Zukoski.  Flame stabilization on bluff bodies at low and intermediate Reynolds numbers , 1954 .

[31]  F. André,et al.  Burner lip temperature and stabilization of a non-premixed jet flame , 2014 .

[32]  Stephen B. Margolis,et al.  Nonlinear stability of combustion-driven acoustic oscillations in resonance tubes , 1992 .

[33]  Wolfgang Polifke,et al.  Fluid Dynamic Instabilities in a Swirl Stabilized Burner and their Effect on Heat Release Fluctuations , 2000 .

[34]  D. A. Santavicca,et al.  Mechanism of Combustion Instability in a Lean Premixed Dump Combustor , 1999 .

[35]  J. P. Longwell,et al.  Flame stabilization by bluff bodies and turbulent flames in ducts , 1953 .

[36]  S. Candel,et al.  A review of active control of combustion instabilities , 1993 .

[37]  D. Spalding.  Theoretical Aspects of Flame Stabilization , 1953 .

[38]  James F. Driscoll,et al.  Enhancement of flame blowout limits by the use of swirl , 1989 .

[39]  S. Basu,et al.  Transition in vortex breakdown modes in a coaxial isothermal unconfined swirling jet , 2014 .

[40]  B. Cetegen,et al.  Blowoff characteristics of bluff-body stabilized conical premixed flames with upstream spatial mixture gradients and velocity oscillations , 2008 .

[41]  Emil J. Hopfinger,et al.  Flow regimes of large-velocity-ratio coaxial jets , 1997, Journal of Fluid Mechanics.

[42]  D. Banerjee,et al.  Theoretical Analysis on Flame Stabilization by a Bluff-Body , 1977 .

[43]  V. Yang,et al.  Bifurcation of flame structure in a lean-premixed swirl-stabilized combustor: transition from stable to unstable flame , 2004 .

[44]  K. Perrakis,et al.  A swirling jet under the influence of a coaxial flow , 2008 .

[45]  R. Adrian,et al.  Effect of resolution on the speed and accuracy of particle image velocimetry interrogation , 1992 .

[46]  Tim Lieuwen,et al.  Characterization of acoustically forced swirl flame dynamics , 2009 .

[47]  Combustion dynamics linked to flame behaviour in a partially premixed swirled industrial burner , 2008 .

[48]  Tim Lieuwen,et al.  Combustion Instabilities In Gas Turbine Engines: Operational Experience, Fundamental Mechanisms, and Modeling , 2006 .

[49]  Ann P. Dowling,et al.  Acoustic Analysis of Gas Turbine Combustors , 2003 .

[50]  V. Yang,et al.  Overview of Combustion Instabilities in Liquid-Propellant Rocket Engines , 1995 .

[51]  János M. Beér,et al.  Combustion in swirling flows: A review , 1974 .

[52]  H. C. Hottel,et al.  Flame stabilization and propagation in high velocity gas streams , 1948 .

[53]  Vigor Yang,et al.  Effect of swirl on combustion dynamics in a lean-premixed swirl-stabilized combustor , 2005 .

[54]  D. Noh,et al.  The effect of CO2 addition on the flame behavior of a non-premixed oxy-methane jet in a lab-scale furnace , 2014 .

[55]  S. Basu,et al.  Transition and acoustic response of recirculation structures in an unconfined co-axial isothermal swirling flow , 2013 .

[56]  R. Adrian,et al.  Flow past a sphere with an oscillation in the free-stream velocity and unsteady drag at finite Reynolds number , 1992, Journal of Fluid Mechanics.

[57]  Y. Yoon,et al.  Flame stabilization in a lifted non-premixed turbulent hydrogen jet with coaxial air , 2010 .

[58]  F. Culick,et al.  Combustion dynamics of a low-swirl combustor , 2007 .

[59]  Qingguo Zhang.  Lean blowoff characteristics of swirling H2/CO/CH4 Flames , 2008 .

[60]  M. Q. McQuay,et al.  An experimental study on the effect of pressure and strain rate on CH chemiluminescence of premixed fuel-lean methane/air flames , 2001 .

[61]  D. Noh,et al.  The effect of hydrogen addition on the flame behavior of a non-premixed oxy-methane jet in a lab-scale furnace , 2013 .

[62]  Tim Lieuwen,et al.  Strain Characteristics Near the Flame Attachment Point in a Swirling Flow , 2009 .

[63]  Ulrich Maas,et al.  Unsteady Combustor Physics , 2014 .

[64]  A. Saha,et al.  Particle image velocimetry and infrared thermography in a levitated droplet with nanosilica suspensions , 2011, Experiments in Fluids.