Structure of the Stabilizing Region of a Laminar Jet Diffusion Flame

Abstract

Velocity, temperature, and composition of major species were measured in the base region of a two-dimensional, laminar methane jet diffusion flame in unconfined still air under a low-velocity jetting condition. The velocity data showed acceleration near the flame zone caused primarily by thermal expansion and buoyancy. The heat flux vectors showed substantial heat flow from the flame base to both downstream and the burner wall. The premixed zone was formed in the dark space by convective penetration of oxygen and back-diffusion of methane. The molar flux vectors of methane and oxygen at the base pointed to the opposite directions, typical of diffusion flames.

Theory of attached and lifted diffusion flames

“…The principles of the DF lifting mechanism are discussed in Refs. 18,19. This theory is later extended.…”

“…The equalspeed configuration has been employed in our model primarily to avoid the complications of a shear flow at the jet exit, thus eliminating vortex shedding, roll-up, intermittency and the formidable problem of oxidizer entrainment, especially in the turbulent case. [18][19][20][21][22] A theory of DF attachment and liftoff has been advanced 30 in which flame stabilization is viewed as the consequence of upstream radical diffusion from the reaction zone. This was determined 29 by the numerical integration of the equations of motion for an axisymmetric round jet, including full chemistry.…”

“…It can also represent flame spread 4 through the use of the conformal mapping ϭsin(z/2), zϭxϩiy, which folds down the side walls while producing a DF that lies close to a radial arc; see The literature of DF attachment is large. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Nonintrusive experimental diagnostics have been applied to this problem. In the development of models, recent emphasis has been placed on mixing and the chemical reaction.…”

Further studies of the reaction kernel structure and stabilization of jet diffusion flames

“…Numerous studies of the structure and stability of laminar diffusion flames have been conducted in both normal earth gravity (1g) and microgravity (lg) [1][2][3][4][5][6][7][8][9][10][11][12]. Although several attempts [1][2][3] were made to reveal the internal structure of the flame-stabilizing region experimentally, most previous works were limited to overall flame characteristics. Qin et al [13] examined the local conditions of the lifted triple flame structure in a partially premixed methane jet.…”

Isolation of Buoyancy Effects in Jet Diffusion Flame Experiments

“…Investigations into the dynamic structure of jet diffusion flames have become more common in the last decade [Yule et al (1981), Eickhoff and Winandy (1985), Roquemore et al (1989), Takahashi et (al. (1988), Chen et al (1988)) This is because these geometrically-simple flames exhibit many features which are generic to more complex combusting flows.…”