scholarly journals Non-Premixed Filtered Tabulated Chemistry: Filtered Flame Modeling of Diffusion Flames

Fuels ◽  
2021 ◽  
Vol 2 (2) ◽  
pp. 87-107
Author(s):  
Pedro Javier Obando Vega ◽  
Axel Coussement ◽  
Amsini Sadiki ◽  
Alessandro Parente
Keyword(s):  
Flame Front ◽  
Diffusion Flame ◽  
Diffusion Flames ◽  
Premixed Combustion ◽  
One Dimensional ◽  
Counterflow Flame ◽  
Tabulated Chemistry ◽  
Laminar Diffusion ◽  
Lift Off ◽  
The One

The flame front filtering is a well-known strategy in turbulent premixed combustion. An extension of this approach for the non-premixed combustion context has been proposed by means of directly filtering counterflow diffusion flamelets. Promising results were obtained for the non-premixed filtered tabulated chemistry formalism on 1-D and 2-D unresolved counterflow flame configurations. The present paper demonstrates the soundness of this approach on a 3-D real laminar non-premixed coflow flame. The model results are compared against the direct filtering of the fully resolved laminar diffusion flame showing that the formalism adequately describes the underlying physics. The study reveals the importance of the one-dimensional counterflow flamelet hypothesis, so that the model activation under this condition is ensured by means of a flame sensor. The consistent coupling between the model and the flame sensor adequately retrieves the flame lift-off and satisfactorily predicts the profile extension due to the filtering process.

scholarly journals The Effects of CO2 Additional on Flame Characteristics in the CH4/N2/O2 Counterflow Diffusion Flame

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 2905
Author(s):  
Ying Chen ◽  
Jingfu Wang ◽  
Xiaolei Zhang ◽  
Conghao Li
Keyword(s):  
Thermal Properties ◽  
Heat Release ◽  
Flame Front ◽  
Release Rate ◽  
Diffusion Flame ◽  
Flame Temperature ◽  
Radiative Properties ◽  
One Dimensional ◽  
Negative Effect ◽  
Counterflow Diffusion Flame

The effects (chemical, thermal, transport, and radiative) of CO2 added to the fuel side and oxidizer side on the flame temperature and the position of the flame front in a one-dimensional laminar counterflow diffusion flame of methane/N2/O2 were studied. Overall CO2 resulted in a decrease in flame temperature whether on the fuel side or on the oxidizer side, with the negative effect being more obvious on the latter side. The prominent effects of CO2 on the flame temperature were derived from its thermal properties on the fuel side and its radiative properties on the oxidizer side. The results also highlighted the differences in the four effects of CO2 on the position of the flame front on different sides. In addition, an analysis of OH and H radicals and the heat release rate of the main reactions illustrated how CO2 affects the flame temperature.

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

Proposal of United Combustion Model for Premixed and Diffusion Flames and Its Evaluation

2008 ◽  
Author(s):  
Shin-Ichi Inage
Keyword(s):  
Diffusion Flame ◽  
Diffusion Flames ◽  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulence Models ◽  
Premixed Combustion ◽  
Combustion Model ◽  
Laminar Flame Speed ◽  
Turbulent Diffusion Flame ◽  
And Diffusion

A premixed flame assisted by the burning of a diffusion flame is used in gas-turbine combustors to reduce NOx emissions. A united model that can be applied to the premixed and diffusion flames is therefore required to simulate the combustion phenomena. This paper proposes such a united model based on the author’s premixed combustion model for reactive progress variable equation. The proposed model has the following features. 1) It includes the laminar flame speed and the gradient of the mixture fraction as parameters. When the gradient of the mixture fraction is close to zero, the model is also close to the previous premixed combustion model as an asymptotic form. 2) It considers the effects of pressure in the combustor, unburned gas temperature, and flame stretch on combustion based on the laminar flame speed. 3) It can be applied to all types of turbulence models like the k-ε model, large eddy simulations, and direct simulations in the case of wrinkled laminar flames. The effect of turbulence is considered through the turbulent eddy viscosity of all turbulence models. To verify the accuracy of the model, the opposed diffusion flame presented by Tsuji and Yamaoka was numerically simulated, as an example of a laminar diffusion flame. Further, a turbulent diffusion flame, which was assisted by the burning of a pilot jet, was demonstrated using the united combustion model as an example of the turbulent diffusion flame discussed by Barlow and Frank. The flame was known as Sandia Flame D. Model results were in good agreement with the experimental data and this agreement confirmed the proposed united model was able to accurately simulate both diffusion flames.

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.

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