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

Extinguishment of methane diffusion flames by carbon dioxide in coflow air and oxygen-enriched microgravity environments

“…Moreover, the flame temperature decreased downstream due to the low reactivity and radiative heat losses. Thus, the vigorously burning reaction kernel sustained stationary combustion processes in the flow in the vicinity of the burner rim (flame attachment) and held the trailing diffusion flame zone downstream, as described in detail elsewhere [18][19][20][21]. The heat-release rate, oxygen consumption rate, velocity, temperature, oxygen mole fraction, local equivalence ratio, and mixture fraction at the reaction kernel wereq k = 177 J/cm 3 s, −ω O 2 ,k = 0.000488 mol/cm 3 s, |v k | = 0.313 m/s, T k = 1478 K, X O 2 ,k = 0.050, φ local,k = 0.61, and ξ k = 0.048, respectively.…”

“…The inner structure of the flame base controls the flame attachment and detachment processes [18][19][20][21][24][25][26][27][28][29]. Fig.…”

“…The contours of both heat-release rate and oxygenconsumption rate showed a peak reactivity spot (the reaction kernel [18][19][20][21]) at the flame base. The chain radical species (H, OH, and O) diffused back against the incoming flow at the flame base (edge), where the oxygen concentration was relatively high compared to that in the trailing diffusion flame.…”

“…The authors have reported the experimental and computational results of the stabilization mechanisms of laminar hydrocarbon jet diffusion flames [18][19][20][21] and the extinguishment of coflow methane diffusion flames by various agents [22][23][24][25][26][27][28][29], in the cup burner configuration [30,31], at normal earth gravity (1g n ) and microgravity (µg). The predicted minimum extinguishing concentration (MEC) of each agent was generally in good agreement (typically within less than ±10%) with the measurement.…”

Cup-burner flame extinguishment by CF3Br and Br2

“…The velocity vectors show the longitudinal acceleration in the hot zone from buoyancy, and as a result of the continuity of the fluid, surrounding air is entrained into the lower part of the flame, inclining the flow streamlines inward due to the low velocity of the fuel flow and the downstream acceleration. Both the heat-release rate and the oxygen-consumption rate contours show a peak reactivity spot (i.e., the reaction kernel [47,64,66]) at the flame base, where the oxygen-rich entrainment flow crosses the flame zone, thus enhancing convective (and diffusive) contributions to the oxygen flux. On the other hand, chain radical species, particularly the H atom, diffuse back against the oxygen-rich incoming flow at the flame base (edge).…”