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Diffusion flame
About: Diffusion flame is a research topic. Over the lifetime, 9266 publications have been published within this topic receiving 233522 citations.
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TL;DR: A brief description of the nature of flame radiation in gas-turbine combustors is given in this article, followed by a discussion on the methods and models available for estimating nonluminous and luminous emissivity.
72 citations
01 Jan 1998
TL;DR: In this paper, an experimental/numerical investigation is performed to explore possible quenching patterns in opposing-jet diffusion flames, where a diluted hydrogen-nitrogen mixture is used as the fuel.
Abstract: Studies on individual vortex-flame interactions constitute important elements for the understanding of the turbulent-flame structure. Vortices having sufficiently high normal velocity can pass through the flame by extinguishing it locally. In several circumstances they deform the flame surface significantly before attaining extinction conditions. The development of curvature on the flame surface, especially in hydrogen flames, could lead to different quenching patterns. An experimental/numerical investigation is performed to explore possible quenching patterns in opposing-jet diffusion flames. A diluted hydrogen-nitrogen mixture is used as the fuel. Vortices are driven toward the flame surface with different velocities from the air side. The changes in the structure of the flame during its interaction with the incoming vortex are recorded by measuring instantaneous OH-concentration field using the laser-induced fluorescence (LIF) technique. A time-dependent CFDC code that incorporates 13 species and 74 reactions is used for the simulation of these vortex-flame interactions. Both the experiments and calculations have identified two types of quenching patterns: namely, point and annular. It is found that when an air-side vortex is forced toward the flame at a relatively high speed, then the flame at the stagnation line quenches, resulting in a well-known point-quenching pattern. On the other hand, when the vortex is forced at a moderate speed, the flame surface deforms significantly, and quenching develops in an annular ring away from the stagnation line, resulting in an unusual annular-quenching pattern. Detailed analyses performed just before the development of annular quenching and 1 ms later suggest that this unusual annular quenching did not result from the strain rate. Based on the understanding gained from previous investigations on curvature effects in coaxial hydrogen jet flames and the findings made in the present study, it is argued that such quenching develops as a result of the combined effect of preferential diffusion and flame curvature.
72 citations
TL;DR: In this paper, the microstructure of soot at larger residence times within a propane-air diffusion flame was investigated using Transmission Electron Microscopy (TEM) using three classes of nanoparticles: primary particles, graphitical particles and elementary particles.
72 citations
01 Jan 2005
TL;DR: The low flame temperature limits for mixing-controlled Diesel combustion were investigated in a constant-volume combustion chamber at well-defined ambient conditions as discussed by the authors, where the ambient gas temperature was less than those of propagating flame processes in engines.
Abstract: The low flame temperature limits for mixing-controlled Diesel combustion were investigated in a constant-volume combustion chamber at well-defined ambient conditions Flame temperatures were controlled by varying ambient oxygen concentration or by using fuel-lean mixing-controlled combustion Pressure rise measurements show that combustion efficiency remains high for flame temperatures as low as 1500–1600 K for conditions where the ambient gas temperature was greater than 1000 K This low flame temperature limit is less than those of propagating flame processes in engines but close to that of HCCI combustion Chemiluminescence imaging shows that a cool flame exists prior to the quasi-steady lift-off length, suggesting that ignition processes are continuously occurring within the Diesel fuel jet as air and fuel mix upstream of the high-temperature reaction zone at the lift-off length
72 citations
01 Jan 2009
TL;DR: In this paper, Cabra et al. used a 2D axisymmetric flow model coupled with the scalar fields, and first order CIVIC was applied to simulate the lifted turbulent jet diffusion flame.
Abstract: Lifted turbulent jet diffusion flame is simulated using Conditional Moment Closure (CMC). Specifically, the burner configuration of Cabra et al. [R. Cabra, T. Myhrvold, J.Y. Chen. R.W. Dibble, A.N. Karpetis, R.S. Barlow, Proc. Combust. Inst. 29 (2002) 1881-1887] is chosen to investigate H-2/N-2 jet flame supported by a vitiated coflow of products of lean H-2/air combustion. A 2D, axisymmetric flow-model fully coupled with the scalar fields, is employed. A detailed chemical kinetic scheme is included, and first order CIVIC is applied. Simulations are carried out for different jet velocities and coflow temperatures (T-c) The predicted liftoff generally agrees with experimental data, as well as joint-PDF results. Profiles of mean scalar fluxes in the mixture fraction space, for T-c = 1025 and 1080 K reveal that (1) Inside the flame zone, the chemical term balances the molecular diffusion term, and hence the Structure is of a diffusion flamelet for both cases. (2) In the pre-flame zone, the structure depends on the coflow temperature: for the 1025 K case, the chemical term being small, the advective term balances the axial turbulent diffusion term. However, for the 1080 K case. the chemical term is large and balances the advective term, the axial turbulent diffusion term being small. It is concluded that, lift-off is controlled (a) by turbulent premixed flame propagation for low coflow temperature while (b) by autoignition for high coflow temperature. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
72 citations