Topic
Diffusion flame
About: Diffusion flame is a research topic. Over the lifetime, 9266 publications have been published within this topic receiving 233522 citations.
Papers published on a yearly basis
Papers
More filters
••
01 Jan 2000TL;DR: In this paper, an edge flame extinction front quickly propagated in the radial direction, turned into an ignition edge flame, and eventually stabilized as a standing triple flame at a radial position larger than the burner radius.
Abstract: Edge flames were investigated in a methane/O 2 /N 2 counterflow diffusion flame burner. In a typical experiment, a stable counterflow diffusion flame in an axysymmetric configuration was perturbed by lowering the relevant Damkohler number slightly below the extinction value, Da ext . As a result, the flame extinguished in the vicinity of the burner axis where conditions were uniform. An edge flame extinction front quickly propagated in the radial direction, turned into an ignition edge flame, and eventually stabilized as a standing triple flame at a radial position larger than the burner radius. This sequence of events resulted from an increase of Da as a function of the radial direction, consequent to a decrease in the strain rate in the radial direction. The edge flame propagation velocity in the ignition mode was measured for propagating edge flames at moderate Da and for standing triple flames at large Da , using a combination of laser Doppler velocimetry of seeded particles, formaldehyde planar laser-induced fluorescence, and natural chemiluminescence imaging. The propagation velocity, nondimensionalized with the premixed laminar flame speed of the unburned stoichiometric mixture, was correlated with Da . The latter was calculated using a thermal diffusive model and velocity measurements. The nondimensional velocity reached a value of 2.6 at large Da , in good agreement with the estimated square root of the ratio of the unburned gas density to the burned gas density, as suggested by scaling considerations.
71 citations
••
01 Jan 2007TL;DR: In this paper, the authors investigated the fuel effects on turbulent premixed flames produced by a gas turbine low-swirl injector (LSI) and showed that the LSI is capable of supporting stable flames that emit x (@ 15% O 2 ).
Abstract: Laboratory experiments have been conducted to investigate the fuel effects on the turbulent premixed flames produced by a gas turbine low-swirl injector (LSI). The lean-blow off limits and flame emissions for seven diluted and undiluted hydrocarbon and hydrogen fuels show that the LSI is capable of supporting stable flames that emit x (@ 15% O 2 ). Analysis of the velocity statistics shows that the non-reacting and reacting flowfields of the LSI exhibit similarity features. The turbulent flame speeds, S T , for the hydrocarbon fuels are consistent with those of methane/air flames and correlate linearly with turbulence intensity. The similarity feature and linear S T correlation provide further support of an analytical model that explains why the LSI flame position does not change with flow velocity. The results also show that the LSI does not need to undergo significant alteration to operate with the hydrocarbon fuels but needs further studies for adaptation to burn diluted H 2 fuels.
71 citations
••
01 Jan 2007TL;DR: In this article, the authors investigated the extinguishment process of methane-air coflow diffusion flames formed on a cup burner in earth gravity and found that flame stabilization at the flame base depended upon diffusion of radicals and heat from the trailing diffusion flame upstream into the peak reactivity spot (i.e., reaction kernel).
Abstract: The extinguishment processes of methane–air coflow diffusion flames formed on a cup burner in earth gravity have been investigated experimentally and computationally. As a gaseous fire-extinguishing agent (CO2, N2, He, Ar, CF3H, CF3Br, or Br2) was introduced gradually into a coflowing oxidizer stream, the base (edge) of the flame detached from the burner rim, oscillated, and eventually extinguished. This extinguishment occurred via a blowoff process (in which the flame base drifted downstream) rather than the global chemical extinction typical of counterflow diffusion flames. The agent concentration in the oxidizer required for extinguishment was nearly independent of the mean oxidizer velocity over a wide range, exhibiting a plateau region. Numerical simulations with full chemistry revealed the unsteady blowoff process and predicted the minimum extinguishing concentration (MEC) of each agent in good agreement with the measurement. The calculations indicated that flame stabilization at the flame base depended upon diffusion of radicals and heat from the trailing diffusion flame upstream into the peak reactivity spot (i.e., reaction kernel). For physically acting agents, the flame blew off as the trailing diffusion flame temperature decreased to ≈1700 K, at which point the back-diffusion of heat and chain radicals into the flame stabilizing region was sufficiently reduced. Consequently, the relative ranking of inert agent effectiveness depended primarily on the heat capacity of the agent-laden oxidizer. Nonetheless, for helium, the MEC was lower than that of argon (which has the same specific heat). The numerical results showed that addition of helium leads to greater heat losses from the downstream diffusion region of the flame than addition of argon because helium addition raised the thermal conductivity of the gas mixture relative to argon addition. The results highlight the importance of the downstream diffusion flame conditions for supporting the flame stabilization which ultimately occurs at the reaction kernel.
71 citations
••
TL;DR: In this paper, the authors evaluated the refractive index of soot generated by a miniCAST, an ethylene diffusion flame, and a PALAS GFG by interpreting specific extinction measurements in the near-UV spectrum with the help of an improved RDG-FA theory.
71 citations
••
TL;DR: In this article, the authors provide an extension of a previous analysis of numerical diffusion of Eulerian schemes to two-dimensional flows in order to shed light on the shortcomings of this approach.
71 citations