Numerical Modeling of a Lifted Laminar Coflow Methane Diffusion Jet Flames Using Detailed Chemistry and Non-Grey Gas Radiation Models

2002 ◽  
Author(s):  
Fengshan Liu ◽  
Hongsheng Guo ◽  
Gregory J. Smallwood
Keyword(s):  
Carbon Dioxide ◽  
Radiation Heat Transfer ◽  
Radiation Absorption ◽  
Discrete Ordinates ◽  
Band Model ◽  
Jet Flames ◽  
Nox Formation ◽  
Model Calculations ◽  
Detailed Chemistry ◽  
Methane Diffusion

Two lifted laminar coflow non-sooting methane diffusion jet flames, one diluted by nitrogen and the other diluted by carbon dioxide, at atmospheric pressure were calculated using detailed chemistry and complex thermal and transport properties. Chemical reactions were modeled using the GRI-Mech 3.0 mechanism with species and reactions related to NOx formation removed. Radiation heat transfer by CO, CO2, and H2O was calculated using the discrete-ordinates method coupled with a statistical narrow-band correlated-k based band model. Calculations of each flame were performed with and without radiation absorption term in the radiative transfer equation in order to provide a quantitative evaluation of the importance of radiation absorption in these two lifted flames. Numerical results show that radiation absorption is relatively unimportant in the nitrogen diluted flame but becomes important in the carbon dioxide diluted flame.

Fuel Stratification Influence on NOx Emission in a Premixed Axial Reacting Jet-in-Crossflow at High Pressure

2021 ◽  
Vol 143 (12) ◽  
Author(s):  
Bernhard Stiehl ◽  
Tommy Genova ◽  
Michelle Otero ◽  
Scott Martin ◽  
Kareem Ahmed
Keyword(s):  
Equivalence Ratio ◽  
Vortex Pair ◽  
No Production ◽  
Nox Formation ◽  
Local Flow ◽  
Detailed Chemistry ◽  
Jet In Crossflow ◽  
Global Emission ◽  
Fuel Stratification ◽  
Jet Trajectory

Abstract Three reacting jet-in-crossflow (JiC) methane/air flames were numerically investigated in a lean axially staged combustor at a pressure of five atmospheres. A detailed chemistry Star-CCM+ computational fluid dynamics (CFD) model was used with 53 species considered and the result of turbulence-governed finite-rate modeling was validated with in-house experimental data. An optically accessible test section features three side windows, allowing local flow and flame analysis with particle image velocimetry (PIV) and CH* chemiluminescence as well as pressure, temperature, and species exit measurements. The research objective was to predict and verify NOx formation of the premixed 12.7 mm axial jet. Three headend temperature levels were investigated along with three premixed jets at lean (φJet = 0.75), near-stoichiometric (φJet = 1.07), and rich (φJet = 1.78) axial fuel line equivalence ratio. Based on the matching exit emission concentration, global emission benefits were investigated by adjustment of the fuel stratification. The perfectly premixed methane/air flames of this study were shown to ignite at the lee-side of the jet. For the elevated headend temperature level T = 1800 K, the flame extended beyond the windward jet trajectory and caused high axial NO production. For industry application, a firing temperature of 1920 K was achieved with a NOx optimized fuel split of 25%, combining a lean headend (φHeadend = 0.61) with a rich (φJet = 1.78) jet equivalence ratio. This operating point allowed minimization of the combustor residence time at temperatures above 1700 K as well as combustion in a compact flame at the jet lee-side along the counter rotating vortex pair.

An Experimental Investigation of the Blowout Limits of a Jet Diffusion Flame in Co-Flowing Streams of Different Velocity and Composition

1993 ◽  
Vol 115 (2) ◽  
pp. 142-147 ◽  
Author(s):  
I. Wierzba ◽  
K. Kar ◽  
G. A. Karim
Keyword(s):  
Carbon Dioxide ◽  
Experimental Investigation ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Diffusion Flame ◽  
Detrimental Effect ◽  
Stream Velocity ◽  
Air Stream ◽  
Methane Diffusion ◽  
Flow Stream

The blowout limits of a methane diffusion flame in a co-flowing air-fuel or air-diluent stream were determined for a range of surrounding co-flow stream velocities, both laminar and turbulent, up to ~ 1.50 m/s. Methane, ethylene, propane and hydrogen were used as the fuels in the surrounding co-flow stream while nitrogen and carbon dioxide were used as diluents. The experimental results show that the velocity of the surrounding stream affects the blowout phenomena significantly. An increase in the stream velocity has a detrimental effect on the blowout limits at very low velocities up to 0.30 m/s (essentially laminar flow) and at velocities higher than 1.50 m/s (turbulent flow). The addition of a fuel to the air stream in most cases enhances the blowout limit of a methane diffusion flame. However, different trends in the variation of the blowout limits with the surrounding fuel concentration were observed, depending on the type of fuel used and on whether the surrounding coflow stream was laminar or turbulent. The addition of nitrogen or carbon dioxide to the air stream results in decreasing the blowout limits. The effect is more severe at the higher velocities.

Radiative Heat Transfer During Growth of Carbon Nanotubes by Vertical Electric-Arc Process

2005 ◽  
Author(s):  
A. G. Ostrogorsky ◽  
L. R. Glicksman
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Optical Thickness ◽  
Radiation Heat Transfer ◽  
Small Diameter ◽  
Side Surface ◽  
Cathode Side ◽  
Discrete Ordinates ◽  
Limited Data ◽  
Electric Arc Process

A macroscopic finite elements model of heat transfer occurring during production of carbon nanotubes was developed. Radiation heat transfer was modeled using the Discrete Ordinates (DO) model and the Rosseland diffusion approximation. The arc is modeled as semitransparent, with the optical thickness ranging from zero to infinity. The results are compared to the limited data available. The optical thickens has a significant impact on the temperature field in (i) the arc and (ii) the anode surfaces exposed to the arc. The temperature of the cathode side-surface on which the small diameter carbon nanotube grew, is not sensitive to the optical thickness of the arc. The model indicates that the optical thickness of the arc should be high, aL ≥ 100.

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 Heat Transfer in Fluidized Beds: A Comparison of Exact and Simplified Approaches

1994 ◽  
Vol 116 (3) ◽  
pp. 652-659 ◽  
Author(s):  
G. Flamant ◽  
J. D. Lu ◽  
B. Variot
Keyword(s):  
Heat Transfer ◽  
Fluidized Beds ◽  
Radiation Heat Transfer ◽  
Discrete Ordinates ◽  
Transfer Model ◽  
Radiation Heat ◽  
Flux Divergence ◽  
Transfer Coefficients ◽  
Variable Porosity ◽  
Radiation Exchange

Radiation heat transfer at heat exchanger walls in fluidized beds has never been examined through a complete formulation of the problem. In this paper a wall-to-bed heat transfer model is proposed to account for particle convection, gas convection, and radiation exchange in a variable porosity medium. Momentum, energy, and intensity equations are solved in order to determine the velocity, temperature, radiative heat flux profiles and heat transfer coefficients. The discrete-ordinates method is used to compute the radiative intensity equation and the radiative flux divergence in the energy equation. Both the gray and the non-gray assumptions are considered, as well as dependent and independent scattering. The exact solution obtained is compared with several simplified approaches. Large differences are shown for small particles at high temperature but the simplified solutions are valid for large particle beds. The dependency of radiative contribution on controlling parameters is discussed.

Sign in / Sign up

Export Citation Format

Share Document