The stability limits of a jet flame can play an important role in the design of burners and combustors. This study details an experiment conducted to determine the liftoff and blowout velocities of oblique-angle methane jet flames under various air coflow velocities. A nozzle was mounted on a telescoping boom to allow for an adjustable burner angle relative to a vertical coflow. Twenty-four flow configurations were established using six burner nozzle angles and four coflow velocities. Measurements of the fuel supply velocity during liftoff and blowout were compared against two parameters: nozzle angle and coflow velocity. The resulting correlations indicated that flames at more oblique angles have a greater upper stability limit and were more resistant to changes in coflow velocity. This behavior occurs due to a lower effective coflow velocity at angles more oblique to the coflow direction. Additionally, stability limits were determined for flames in crossflow and mild counterflow configurations, and a relationship between the liftoff and blowout velocities was observed. For flames in crossflow and counterflow, the stability limits are higher. Further studies may include more angle and coflow combinations, as well as the effect of diluents or different fuel types. 1. Introduction A multitude of studies have been performed on lifted jet flames and their behavior in various air flow configurations. In such partially premixed flames, the characteristics of the surrounding air flow (velocity, temperature) can strongly impact the overall combustion process and the stability parameters. As fuel flows from a nozzle and mixes with the air, the fuel and oxidizer concentrations vary throughout space and time. The extent of mixing due to turbulence also changes depending on the surrounding flow. The perpetually varying concentrations help to determine the overall behavior of a flame: its shape, velocity, size, color, temperature, and composition. In parallel, the heat release serves to laminarize regions and serves to limit reducing mixing. In particular, two important behavioral parameters are liftoff and blowout velocity. Initially, a jet flame will remain attached to the nozzle at low fuel velocities. However, at a critical jet velocity, the flame will lift off from the nozzle and stabilize at a position downstream due to the inability of the flame to remain anchored on the burner [1]. While there is, in general, a regime where the flame can stabilize, increasing the jet velocity will ultimately lead to blowout, in which the flame is extinguished. This behavior
References
[1]
K. K. Kuo, Principles of Combustion, Wiley-Interscience, New York, NY, USA, 2nd edition, 2005.
[2]
K. Wohl, N. M. Kapp, and C. Gazley, “The stability of open flames,” Symposium on Combustion and Flame, and Explosion Phenomena, vol. 3, no. 1, pp. 3–21, 1949.
[3]
L. Vanquickenborne and A. van Tiggelen, “The stabilization mechanism of lifted diffusion flames,” Combustion and Flame, vol. 10, no. 1, pp. 59–69, 1966.
[4]
G. T. Kalghatgi, “Lift-off heights and visible lengths of vertical turbulent jet diffusion flames in still air,” Combustion Science and Technology, vol. 41, pp. 17–29, 1984.
[5]
C. D. Brown, K. A. Watson, and K. M. Lyons, “Studies on lifted jet flames in coflow: the stabilization mechanism in the near- and far-fields,” Flow, Turbulence and Combustion, vol. 62, no. 3, pp. 249–273, 1999.
[6]
S. R. Tieszen, D. W. Stamps, and T. J. O'Hern, “A heuristic model of turbulent mixing applied to blowout of turbulent jet diffusion flames,” Combustion and Flame, vol. 106, no. 4, pp. 442–466, 1996.
[7]
C. P. Burgess and C. J. Lawn, “The premixture model of turbulent burning to describe lifted jet flames,” Combustion and Flame, vol. 119, no. 1-2, pp. 95–108, 1999.
[8]
S. Navarro-Martinez and A. Kronenburg, “Analysis of stabilization mechanisms in lifted flames,” in International COST Conference on Les and DNS of Ignition Complex-Structure Flames with Local Extinction, pp. 13–38, pol, November 2008.
[9]
R. V. Bandaru and S. R. Turns, “Turbulent jet flames in a crossflow: Effects of some jet, crossflow, and pilot-flame parameters on emissions,” Combustion and Flame, vol. 121, no. 1-2, pp. 137–151, 2000.
[10]
G. T. Kalghatgi, “Blow-out stability of gaseous jet diffusion flames part II: effect of cross wind,” Combustion Science and Technology, vol. 26, no. 5-6, pp. 241–244, 1981.
[11]
G. T. Kalghatgi, “Blow-out stability of gaseous jet diffusion flames part III: effect of burner orientation to wind direction,” Combustion science and technology, vol. 28, no. 5 /6, pp. 241–245, 1982.
[12]
D. Han and M. G. Mungal, “Simultaneous measurements of velocity and CH distribution. Part II: Deflected jet flames,” Combustion and Flame, vol. 133, no. 1-2, pp. 1–17, 2003.
[13]
E. F. Hasselbrink and M. G. Mungal, “Transverse jets and jet flames. Part 2. Velocity and OH field imaging,” Journal of Fluid Mechanics, vol. 443, pp. 27–68, 2001.
[14]
J. L. McCraw, Observations on upstream flame propagation in ignited hydrocarbon jets, M.S. thesis, Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, USA, 2006.
[15]
S. D. Terry and K. M. Lyons, “Low Reynolds Number turbulent lifted flames in high co-flow,” Combustion Science and Technology, vol. 177, no. 11, pp. 2091–2112, 2005.
[16]
R. F. Huang and S. M. Wang, “Characteristic flow modes of wake-stabilized jet flames in a transverse air stream,” Combustion and Flame, vol. 117, no. 1-2, pp. 59–77, 1999.
[17]
N. J. Moore, J. Kribs, and K. M. Lyons, “Investigation of Jet-Flame Blowout with Lean-Limit Considerations,” Flow, Turbulence and Combustion, pp. 1–12, 2011.
[18]
S. Lamige, C. Galizzi, J. Min, et al., “Effect of reactant preheating on the stability of non-premixed methane/air flames,” in Proceedings of the International Heat Transfer Conference, Washington, DC, USA, 2010.
