An Analysis of Lift-Off in Laminar Diffusion Flames

2001 ◽  
Author(s):  
Sally A. Cheatham ◽  
Elaine S. Oran
Keyword(s):  
Diffusion Flames ◽  
Laminar Diffusion Flames ◽  
Laminar Diffusion ◽  
Lift Off

scholarly journals A comparison of computational and experimental lift-off heights of coflow laminar diffusion flames

2005 ◽  
Vol 30 (1) ◽  
pp. 357-365 ◽  
Author(s):  
Kevin T. Walsh ◽  
Joseph Fielding ◽  
Mitchell D. Smooke ◽  
Marshall B. Long ◽  
Amable Liñán
Keyword(s):  
Diffusion Flames ◽  
Laminar Diffusion Flames ◽  
Laminar Diffusion ◽  
Lift Off

Effects of Flame Lift-Off Height on Soot Processes in Strongly Forced Methane-Air Laminar Diffusion Flames

2007 ◽  
Author(s):  
Vinayak V. Barve ◽  
Ofodike A. Ezekoye ◽  
Noel T. Clemens
Keyword(s):  
Diffusion Flames ◽  
Discrete Ordinates ◽  
Strong Mixing ◽  
Mixing Processes ◽  
Mean Velocity ◽  
Laminar Diffusion Flames ◽  
Laminar Diffusion ◽  
Forced Jets ◽  
Lift Off ◽  
Air Diffusion

Previous work has shown that for sufficiently high periodic forcing amplitudes, laminar diffusion flames can burn in an effectively partially premixed mode. Experimental observations show that the luminosity and sooting properties of the forced flames are significantly modified by the presence of strong forcing. In this work, simulations are performed to study the effects of strong forcing on flow field development in strongly forced laminar isothermal jets and methane air diffusion flames. Unforced and strongly forced cold-flow jets are simulated using a higher order finite volume CFD code. The jet was forced by varying the jet exit velocity over a range of forcing amplitudes and frequencies and it was found that the jet Strouhal number (St) was the important parameter in characterizing flowfield development. Further, the forced jets showed increased entrainment and increased entrainment rates as compared to the non-forced jets. The computations are performed for laminar methane–air diffusion flames. The combustion reactions were modeled using detailed gas-phase chemistry and complex thermo-physical properties. The radiation heat transfer was modeled using the S-6 Discrete Ordinates Method. A 2 equation soot chemistry model for soot nucleation, surface growth and oxidation was used. First an unforced flickering methane–air diffusion flame was modeled and then the flame was forced by varying the amplitude and frequency of the fuel velocity in the nozzle. Cases where the peak velocity in the fuel stream reached 6 times the mean velocity are examined. The internal nozzle flow was also simulated since the near-nozzle region was of particular interest due to the strong mixing processes occurring there and the subsequent effect on the flame properties. Lifted forced flames were also examined, and it was found that the partial premixing in the near nozzle region and increased oxygen entrainment in the forced flames can explain the reduction in soot production for the strongly forced flames.

scholarly journals The influence of aliphatics on soot inception modelling

2021 ◽  
Author(s):  
Nemanja Ceranic
Keyword(s):  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Fluid Dynamic ◽  
Soot Volume Fraction ◽  
Surface Reactivity ◽  
Complex Nature ◽  
Laminar Diffusion Flames ◽  
Laminar Diffusion ◽  
Polycyclic Aromatic

Soot models have been investigated for several decades and many fundamental models exist that prescribe soot formation in agreement with experiments and theories. However, due to the complex nature of soot formation, not all pathways have been fully characterized. This work has numerically studied the influence that aliphatic based inception models have on soot formation for coflow laminar diffusion flames. CoFlame is the in-house parallelized FORTRAN code that was used to conduct this research. It solves the combustion fluid dynamic conservation equations for a variety of coflow laminar diffusion flames. New soot inception models have been developed for specific aliphatics in conjunction with polycyclic aromatic hydrocarbon based inception. The purpose of these models was not to be completely fundamental in nature, but more so a proof-of-concept in that an aliphatic based mechanism could account for soot formation deficiencies that exist with just PAH based inception. The aliphatic based inception models show potential to enhance predicative capability by increasing the prediction of the soot volume fraction along the centerline without degrading the prediction along the pathline of maximum soot. Additionally, the surface reactivity that was used to achieve these results lied closer in the range of numerically derived optimal values as compared to the surface reactivity that was needed to match peak soot concentrations without the aliphatic based inception models.

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