97/03069 Radiation extinction limit of counterflow premixed lean methane-air flames

1997 ◽  
Vol 38 (4) ◽  
pp. 252
Keyword(s):  
Extinction Limit ◽  
Radiation Extinction

Analysis of Radiation Reabsorption Effects on Flame Characteristics and NOx Emission in Laminar Flames

2010 ◽  
Author(s):  
Jingfu Wang ◽  
Guoqiang Li
Keyword(s):  
Flame Temperature ◽  
Laminar Flames ◽  
Radiative Properties ◽  
Band Model ◽  
Nox Formation ◽  
Flame Thickness ◽  
Radiation Heat Loss ◽  
Extinction Limit ◽  
Radiation Extinction ◽  
Radiation Reabsorption

The radiation reabsorption effects on NOx formation and flame characteristics in CH4/Air laminar flames were numerically investigated by using full chemistry mechanism and detailed transport properties. The radiative gases were treated as non-gray gas and their spectral radiative properties were evaluated by means of the statistical narrow-band model. The radiative heat transfer equation was solved by the discrete ordinate method. It was found that the reabsorption of emitting radiation leads to substantially wider flame thickness and higher flame temperature than those calculated by using the optically thin model, and the radiation reabsorption effect on the “radiation extinction limit” becomes more important. The results show that the level of NOx is predicted to be highest in the adiabatic flames, that is, flames without radiation heat loss, and that the level of NOx is predicted to be lowest in the flames by the optically thin model. In the flames by the SNB model, the predicted amount of NOx lies between these two levels. The calculated results also show that the radiation reabsorption effect on NOx formation grows stronger as the stretch rate decreases, particularly when CO2, a strong absorber, is added to the unburned gas mixture. In this study, the effectiveness and validity of the optically thin radiation model for calculating NOx formation in laminar flames was also investigated in comparison with the SNB model.

Radiation extinction limit of counterflow premixed lean methane-air flames

1997 ◽  
Vol 109 (4) ◽  
pp. 639-646 ◽  
Author(s):  
Hongsheng Guo ◽  
Yiguang Ju ◽  
Kaoru Maruta ◽  
Takashi Niioka ◽  
Fengshan Liu
Keyword(s):  
Extinction Limit ◽  
Radiation Extinction

On the extinction limit and flammability limit of non-adiabatic stretched methane–air premixed flames

1997 ◽  
Vol 342 ◽  
pp. 315-334 ◽  
Author(s):  
YIGUANG JU ◽  
HONGSHENG GUO ◽  
KAORU MARUTA ◽  
FENGSHAN LIU
Keyword(s):  
Equivalence Ratio ◽  
Flame Temperature ◽  
Lewis Number ◽  
Flammability Limit ◽  
Radiative Heat Loss ◽  
Stretch Rate ◽  
Stable Branch ◽  
Extinction Limit ◽  
Radiation Extinction ◽  
Normal Flame

Extinction limits and the lean flammability limit of non-adiabatic stretched premixed methane–air flames are investigated numerically with detailed chemistry and two different Planck mean absorption coefficient models. Attention is paid to the combined effect of radiative heat loss and stretch at low stretch rate. It is found that for a mixture at an equivalence ratio lower than the standard lean flammability limit, a moderate stretch can strengthen the combustion and allow burning. The flame is extinguished at a high stretch rate due to stretch and is quenched at a low stretch rate due to radiation loss. A O-shaped curve of flame temperature versus stretch rate with two distinct extinction limits, a radiation extinction limit and a stretch extinction limit respectively on the left- and right-hand sides, is obtained. A C-shaped curve showing the flammability limit of the stretched methane–air flame is obtained by plotting these two extinction limits in the mixture strength coordinate. A good agreement is shown on comparing the predicted results with the experimental data. For equivalence ratio larger than a critical value, it is found that the O-shaped temperature curve opens up in the middle of the stable branch, so that the stable branch divides into two stable flame branches; a weak flame branch and a normal flame branch. The weak flame can survive between the radiation extinction limit and the opening point (jump limit) while the normal flame branch can survive from its stretch extinction limit to zero stretch rate. Finally, a G-shaped curve showing both extinction limits and jump limits of stretched methane–air flames is presented. It is found that the critical equivalence ratio for opening up corresponds to the standard flammability limit measured in microgravity. Furthermore, the results show that the flammability limit (inferior limit) of the stretched methane–air flame is lower than the standard flammability limit because flames are strengthened by a moderate stretch at Lewis number less than unity.

scholarly journals Introduction of Fractal-Based Tree Digitalization and Accurate In-Canopy Radiation Transfer Modelling to the Microclimate Model ENVI-met

Forests ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 869
Author(s):  
Helge Simon ◽  
Tim Sinsel ◽  
Michael Bruse
Keyword(s):  
Radiation Transfer ◽  
Numerical Models ◽  
Diffuse Radiation ◽  
Secondary Sources ◽  
Plant Canopies ◽  
Wall Structures ◽  
Transfer Modelling ◽  
Branching System ◽  
Lindenmayer System ◽  
Radiation Extinction

While complex urban morphologies including different materials, wall structures, etc., are rather adequately represented in microclimate models, replication of actual plant geometry is—so far—rather crudely handled. However, plant geometry greatly differs within species and locations while strongly determining a plant’s microclimate performance. To improve the plants representation in numerical models, a new method to describe plant skeletons using the so-called Lindenmayer-System has been implemented in the microclimate model ENVI-met. The new model allows describing much more realistic plants including the position and alignment of leaf clusters, a hierarchical description of the branching system and the calculation of the plant’s biomechanics. Additionally, a new canopy radiation transfer module is introduced that allows not only the simulation of diffuse radiation extinction but also secondary sources of diffuse radiation due to scattering of direct radiation within plant canopies. Intercomparisons between model runs with and without the advancements showed large differences for various plant parameters due to the introduction of the Lindenmayer-System and the advanced radiation scheme. The combination of the two developments represents a sophisticated approach to accurately digitize plants, model radiative transfer in crown canopies, and thus achieve more realistic microclimate results.

Energetic and Polarization Features of the Visible and Near-IR Radiation Extinction by Large Crystals

2015 ◽  
Vol 57 (10) ◽  
pp. 1364-1373 ◽  
Author(s):  
O. V. Shefer
Keyword(s):  
Ir Radiation ◽  
Near Ir ◽  
Radiation Extinction

Virtual enclosure model for thermal radiation extinction inside porous materials with closed cell structure

2015 ◽  
Vol 87 ◽  
pp. 79-91 ◽  
Author(s):  
Ari Seppälä ◽  
Olli Vartia ◽  
Pyry Seppälä ◽  
Kari Saari ◽  
Tuula Noponen ◽  
...  
Keyword(s):  
Thermal Radiation ◽  
Porous Materials ◽  
Cell Structure ◽  
Closed Cell ◽  
Radiation Extinction

Co Emission Modeling in a Heavy Duty Annular Combustor Operating with Natural Gas

2021 ◽  
Author(s):  
Roberto Meloni ◽  
Stefano Gori ◽  
Antonio Andreini ◽  
Pier Carlo Nassini
Keyword(s):  
Turbulent Flame ◽  
Flame Temperature ◽  
Production Region ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
Extinction Limit ◽  
Flamelet Generated Manifold ◽  
Annular Combustor ◽  
Definition Of ◽  
Co Emission

Abstract The present paper summarizes the development of a Large-Eddy Simulation (LES) based approach for the prediction of CO emission in an industrial gas turbine combustor. Since the operating point of the modern combustors is really close to the extinction limit, the availability of a tool able to detect the onset of high-CO production can be useful for the proper definition of the combustion chamber air split or to introduce design improvements for the premixer itself. The accurate prediction of CO cannot rely on the flamelet assumption, representing the fundament of the modern combustion models. Consequently, in this work, the Extended Turbulent Flame Speed Closure (ETFSC) of the standard Flamelet Generated Manifold (FGM) model is employed to consider the effect of the heat loss and the strain rate on the flame brush. Moreover, a customized CO-Damköhler number is introduced to de-couple the in-flame CO production region from the post-flame contribution where the oxidation takes place. A fully premixed burner working at representative values of pressure and flame temperature of an annular combustor is selected for the validation phase of the process. The comparison against the experimental data shows that the process is not only able to capture the trend but also to predict CO in a quantitative manner. In particular, the interaction between the flame and the air fluxes at some critical sections of the combustor, leading the CO emission from the equilibrium value to the super-equilibrium, has been correctly reproduced.

scholarly journals Extinction Limit of Diffusion Microflames

2010 ◽  
Vol 36 (5) ◽  
pp. 214-221
Author(s):  
Kazunori KUWANA ◽  
Tamio IDA
Keyword(s):  
Extinction Limit

Growth and yield differences between triazine-tolerant and non-triazine-tolerant cultivars of canola

2002 ◽  
Vol 53 (6) ◽  
pp. 643 ◽  
Author(s):  
M. J. Robertson ◽  
J. F. Holland ◽  
S. Cawley ◽  
T. D. Potter ◽  
W. Burton ◽  
...  
Keyword(s):  
Harvest Index ◽  
Growth Analysis ◽  
Oil Content ◽  
Cropping Systems ◽  
Growth And Yield ◽  
Physiological Basis ◽  
Use Efficiency ◽  
The Difference ◽  
Radiation Extinction ◽  
Radiation Use

Canola tolerant to the triazine group of herbicides is grown widely in Australian broad-acre cropping systems. Triazine-tolerant (TT) cultivars are known to have a yield and oil content penalty compared with non-TT cultivars. This study was designed to elucidate the crop physiological basis for the yield differences between the two types. Two commercial cultivars, near-isogenic for the TT trait, were compared in a detailed growth analysis in the field, and 22 crops were compared for phenology and crop attributes at maturity. In the growth analysis study, the TT trait was found to lower radiation use efficiency, which carried through to less biomass at maturity. There were minimal effects on leaf area development and harvest index, and no effect on canopy radiation extinction. Across the 22 crops, where yield varied from 240 to 3400 kg/ha in the non-TT cultivar, yield was on average 26% less in the TT cultivar due to less biomass produced, as there was no significant effect on harvest index. The difference in oil content (2-5%) was greater in low oil content environments. Flowering was delayed by 2-10 days with a greater delay being in later flowering environments. Quantification of the physiological attributes of TT canola allows the assessment of the productivity of different cultivar types across environments.

Production of Diffusion Flames in the Near Extinction Limit Regime Using a Hele-Shaw Apparatus in a Simulated Low Gravity Environment

2001 ◽  
Author(s):  
Lisa M. Oravecz-Simpkins ◽  
Indrek S. Wichman
Keyword(s):  
Diffusion Flames ◽  
Space Station ◽  
Scaling Analysis ◽  
Test Results ◽  
Low Gravity ◽  
Flame Instability ◽  
Extinction Limit ◽  
Maximum Test ◽  
Near Extinction ◽  
Flame Instabilities

Abstract A Hele-Shaw apparatus that produced spreading diffusion flames in the near extinction limit was designed and constructed. A scaling analysis was used to determine the maximum test section height for which effects of gravity could be neglected. Preliminary results showed that this apparatus could be used to produce flame instabilities which resemble drop tower test results from NASA [1,2] and other diffusion flame instability studies [3,4,5,6]. Therefore, the Hele-Shaw apparatus is useful for studying flames in a simulated low gravity environment. Additional unstable behaviors seen in the device, such as flame pulsing and spreading blue cusps, not in the NASA testing further supported the need for investigations during longer microgravity times on the International Space Station. The initial testing was only used to gain an observable region of unstable flames. Further studies will be directed at explaining and quantifying specific behaviors with test conditions.

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