Diffusion flame

About: Diffusion flame is a research topic. Over the lifetime, 9266 publications have been published within this topic receiving 233522 citations.

The burning rate’s effect on the flame length of weak fire whirls

Abstract: This paper discusses why the visibly-determined flame length of a weak fire whirl increases as compared with the corresponding pool fire without spin. Here, a fire whirl is called weak when the pure aerodynamic effect of flow circulation has a negligible influence on the flame length. Split cylinders were used to apply a flow circulation to a 3-cm-diameter methane burner flame and a 3-cm-diameter ethanol pool fire. After applying the flow circulation, the flame length of the ethanol pool fire increased about three times, while little change was observed in the flame length of the methane burner flame. The difference is explained by the fact that the burning rate of the methane burner flame was fixed constant, whereas that of the ethanol pool fire increased due to the increased heat input to the fuel surface caused by a change in flame shape pushed toward the fuel surface. The experimental observations thus demonstrate that the burning-rate effect can significantly increase the flame length even under a weak circulation condition. Computational fluid dynamics (CFD) simulations were conducted to understand the detailed flow structure of a fire whirl. An analytical model was then developed based on the experimental observations and CFD calculations; the predicted relationship between the flame height and the burning rate agreed with experimental data.

Flame characteristics of turbulent lean premixed methane/air flames at high pressure: Turbulent flame speed and flame brush thickness

Abstract: The effects of operating conditions and turbulence on flame front position, turbulent flame speed and flame brush thickness of lean premixed methane/air flames at high pressure are investigated experimentally. A comparison of the measured turbulent flame speeds with existing correlations is presented and discussed. The measurements were performed in an axis-symmetric, generic combustor at pressures up to p = 1.44 MPa, equivalence ratios in the range Φ = 0.43–0.56, preheating temperatures T = 673–773 K and for an inlet bulk velocity range of u BULK = 30–60 m/s. The turbulence intensity and the integral length scale at the combustor inlet were varied by means of turbulence grids with different geometry and by changing the grid position in the inlet channel. The isothermal flow field was characterized by two-dimensional particle image velocimetry (PIV). The characterization of the flame front was based on the statistical analysis of two-dimensional instantaneous images of the laser induced fluorescence of the OH radical (OH-PLIF). The analyses revealed that pressure has no effect on the flame front position, the turbulent flame speed, or on the flame front fluctuation (flame brush thickness). Decreasing the fuel concentration from Φ = 0.43 to Φ = 0.56 results in a flame elongation by a factor of 2 and a corresponding decrease of the turbulent flame speed by a factor of 3. For the same variation of the fuel concentration the flame brush thickness increases by a factor of 2. Additionally, the flame brush thickness was consistently observed to vary proportionally to the square root of the flame front position. The experimental values of the turbulent flame speed are in satisfactory agreement with the existing correlations.