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 2015TL;DR: In this article, the growth of an unburned mixture finger (UMF), which deeply intrudes into combustion products, is controlled by a physical mechanism of flame-flow interaction that has not yet been highlighted in the turbulent combustion literature.
Abstract: Data obtained in 3D direct numerical simulations of statistically planar, 1D premixed turbulent flames indicate that the global burning velocity, flame surface area, and the mean flame brush thickness exhibit significant large-scale oscillations with time. Analysis of the data shows that the oscillations are caused by origin, growth, and subsequent disappearance of elongated channels filled by unburned gas. The growth of such an unburned mixture finger (UMF), which deeply intrudes into combustion products, is controlled by a physical mechanism of flame-flow interaction that has not yet been highlighted in the turbulent combustion literature, to the best of the present authors knowledge. More specifically, the fingers grow due to strong axial acceleration of unburned gas by local pressure gradient induced by heat release in surrounding flamelets. Under conditions of the present DNS, this physical mechanism plays an important role by producing at least as much flame surface area as turbulence does when the density ratio is equal to 7.5. Although, similarly to the Darrieus-Landau (DL) instability, the highlighted physical mechanism results from the interaction between a premixed flame and pressure field, it is argued that the UMF and the DL instability are different manifestations of the aforementioned interaction. Disappearance of an UMF is mainly controlled by the high-speed self-propagation of strongly inclined flame fronts (cusps) to the leading edge of the flame brush, but significant local increase in displacement speed due to large negative curvature of the front plays an important role also.
66 citations
••
TL;DR: In this article, the stability limits of confined jet diffusion flames (JDFs) flowing into a co-axial oxidizing stream was studied both experimentally and analytically.
66 citations
••
TL;DR: In this paper, the effect of hydrogen addition on the temperature field is moderate (maximum increase ∼ 100 K ), the effect being greater when hydrogen is premixed with acetylene and hydrogen addition.
66 citations
••
TL;DR: In this paper, the authors investigated the combustion characteristics of porous heating burners under both steady-state and transient conditions and found that the flame speed in a porous heating burner decreases with an increase in the length of the porous bed.
66 citations
••
01 Jan 2009TL;DR: In this article, two types of round jet are examined under acoustic forcing and the authors focus on the heat release of the jet diffusion flame, which oscillates at the same natural frequency as the bulging mode.
Abstract: In this experimental and numerical study, two types of round jet are examined under acoustic forcing. The first is a non-reacting low density jet (density ratio 0.14). The second is a buoyant jet diffusion flame at a Reynolds number of 1100 (density ratio of unburnt fluids 0.5). Both jets have regions of strong absolute instability at their base and this causes them to exhibit strong self-excited bulging oscillations at well-defined natural frequencies. This study particularly focuses on the heat release of the jet diffusion flame, which oscillates at the same natural frequency as the bulging mode, due to the absolutely unstable shear layer just outside the flame. The jets are forced at several amplitudes around their natural frequencies. In the non-reacting jet, the frequency of the bulging oscillation locks into the forcing frequency relatively easily. In the jet diffusion flame, however, very large forcing amplitudes are required to make the heat release lock into the forcing frequency. Even at these high forcing amplitudes, the natural mode takes over again from the forced mode in the downstream region of the flow, where the perturbation is beginning to saturate non-linearly and where the heat release is high. This raises the possibility that, in a flame with large regions of absolute instability, the strong natural mode could saturate before the forced mode, weakening the coupling between heat release and incident pressure perturbations, hence weakening the feedback loop that causes combustion instability.
66 citations