Analysis of flame structure using detailed chemistry and applicability of flamelet/progress variable model in the laminar counter-flow diffusion flames of pulverized coals

The reduction of nitrogen oxides in the high temperature flame is the key factor affecting the oxygen-enriched combustion performance. A numerical study using an OPPDIF code with detailed chemistry mechanism GRI 3.0 was carried out to focus on the effect of strain rate (25-130 s?1) and CO2 addition (0-0.59) on the oxidizer side on NO emission in CH4 / N2 / O2 counter-flow diffusion flame. The mole fraction profiles of flame structures, NO, NO2 and some selected radicals (H, O, OH) and the sensitivity of the dominant reactions contributing to NO formation in the counter-flow diffusion flames of CH4\/ N2 /O2 and CH4 / N2 / O2 / CO2 were obtained. The results indicated that the flame temperature and the amount of NO were reduced while the sensitivity of reactions to the prompt NO formation was gradually increased with the increasing strain rate. Furthermore, it is shown that with the increasing CO2 concentration in oxidizer, CO2 was directly involved in the reaction of NO consumption. The flame temperature and NO production were decreased dramatically and the mechanism of NO production was transformed from the thermal to prompt route.

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B132 Arrangement of Flame Structure by Reaction Progress Variable and Its Gradient in Unsteady Counter-flow Premixed Flame When Changing Equivalence Ratio

The Proceedings of the Thermal Engineering Conference ◽

10.1299/jsmeted.2005.63 ◽

2005 ◽

Vol 2005 (0) ◽

pp. 63-64

Author(s):

Naoki Hayashi ◽

Hiroshi Yamashita ◽

Yuji Nakamura ◽

Kazuhiro Yamamoto

Keyword(s):

Equivalence Ratio ◽

Flame Structure ◽

Premixed Flame ◽

Counter Flow ◽

Reaction Progress ◽

Progress Variable

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Numerical study of the effects of radiative heat losses on diffusion flames

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1243/09544062jmes118 ◽

2006 ◽

Vol 220 (8) ◽

pp. 1189-1199

Author(s):

M D Gaustad ◽

T Shamim

Keyword(s):

Radiation Effects ◽

Diffusion Flames ◽

Numerical Study ◽

Flame Structure ◽

Combustion Products ◽

Chemical Mechanism ◽

Strain Rates ◽

Detailed Chemistry ◽

Extinction Limit ◽

Radiative Losses

The effects of thermal radiation are numerically investigated for a methane-air counterflow diffusion flame, using ‘detailed’ chemistry. The radiative losses from combustion products (CO2 and H2O) were considered by using a thin gas approximation. The results show a significant effect of radiative losses causing extinction at low strain rates. On the basis of the radiative losses from gaseous combustion products, an extinction limit was found to be 0.7 s−1. The presence of soot will move this limit to higher strain rates. The radiation effects are relatively less at moderate and high strain rates, where they may cause a reduction in the peak temperatures by ∼ 10 per cent. In addition to decreasing peak temperatures and combustion products, the radiative losses also reduce the flame width. The results show the importance of including detailed chemical mechanism in correctly predicting the extinction limit and the influence of radiative losses on flame structure.

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Comparison of Flame Propagation Statistics Based on Direct Numerical Simulation of Simple and Detailed Chemistry. Part 2: Influence of Choice of Reaction Progress Variable

Energies ◽

10.3390/en14185695 ◽

2021 ◽

Vol 14 (18) ◽

pp. 5695

Author(s):

Felix B. Keil ◽

Marvin Amzehnhoff ◽

Umair Ahmed ◽

Nilanjan Chakraborty ◽

Markus Klein

Keyword(s):

Numerical Simulation ◽

Direct Numerical Simulation ◽

Flame Propagation ◽

Flame Structure ◽

Tangential Strain ◽

Detailed Chemistry ◽

Reaction Progress ◽

Considerable Uncertainty ◽

Progress Variable ◽

Displacement Speed

Flame propagation statistics for turbulent, statistically planar premixed flames obtained from 3D Direct Numerical Simulations using both simple and detailed chemistry have been evaluated and compared to each other. To achieve this, a new database has been established encompassing five different conditions on the turbulent combustion regime diagram, using nearly identical numerical methods and the same initial and boundary conditions. The discussion includes interdependencies of displacement speed and its individual components as well as surface density function (i.e., magnitude of the reaction progress variable) with tangential strain rate and curvature. For the analysis of detailed chemistry Direct Numerical Simulation data, three different definitions of reaction progress variable, based on CH4,H2O and O2 mass fractions will be used. While the displacement speed statistics remain qualitatively and to a large extent quantitatively similar for simple chemistry and detailed chemistry, there are pronounced differences for its individual contributions which to a large extent depend on the definition of reaction progress variable as well as on the chosen isosurface level. It is concluded that, while detailed chemistry simulations provide more detailed information about the flame structure, the choice of the reaction progress variable definition and the choice of the resulting isosurface give rise to considerable uncertainty in the interpretation of displacement speed statistics, sometimes even showing opposing trends. Simple chemistry simulations are shown to provide (a) the global flame propagation statistics which are qualitatively similar to the corresponding results from detailed chemistry simulations, (b) remove the uncertainties with respect to the choice of reaction progress variable, and (c) are more straightforward to compare with theoretical analysis or model assumptions that are mostly based on simple chemistry assumptions.

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Nitric oxide formation in strained laminar hydrogen-air counter flow diffusion flames

10.2514/6.1995-132 ◽

1995 ◽

Author(s):

J Zhao ◽

K Isaac

Keyword(s):

Nitric Oxide ◽

Diffusion Flames ◽

Oxide Formation ◽

Counter Flow ◽

Nitric Oxide Formation

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Effect of the Preheated Oxidizer Temperature on Soot Formation and Flame Structure in Turbulent Methane-Air Diffusion Flames at 1 and 3 atm: A CFD Investigation

Energies ◽

10.3390/en14123671 ◽

2021 ◽

Vol 14 (12) ◽

pp. 3671

Author(s):

Subrat Garnayak ◽

Subhankar Mohapatra ◽

Sukanta K. Dash ◽

Bok Jik Lee ◽

V. Mahendra Reddy

Keyword(s):

Mole Fraction ◽

Air Temperature ◽

Reaction Rate ◽

Volume Fraction ◽

Diffusion Flames ◽

Soot Formation ◽

Flame Structure ◽

Soot Volume Fraction ◽

Computational Domain ◽

Pressure Elevation

This article presents the results of computations on pilot-based turbulent methane/air co-flow diffusion flames under the influence of the preheated oxidizer temperature ranging from 293 to 723 K at two operating pressures of 1 and 3 atm. The focus is on investigating the soot formation and flame structure under the influence of both the preheated air and combustor pressure. The computations were conducted in a 2D axisymmetric computational domain by solving the Favre averaged governing equation using the finite volume-based CFD code Ansys Fluent 19.2. A steady laminar flamelet model in combination with GRI Mech 3.0 was considered for combustion modeling. A semi-empirical acetylene-based soot model proposed by Brookes and Moss was adopted to predict soot. A careful validation was initially carried out with the measurements by Brookes and Moss at 1 and 3 atm with the temperature of both fuel and air at 290 K before carrying out further simulation using preheated air. The results by the present computation demonstrated that the flame peak temperature increased with air temperature for both 1 and 3 atm, while it reduced with pressure elevation. The OH mole fraction, signifying reaction rate, increased with a rise in the oxidizer temperature at the two operating pressures of 1 and 3 atm. However, a reduced value of OH mole fraction was observed at 3 atm when compared with 1 atm. The soot volume fraction increased with air temperature as well as pressure. The reaction rate by soot surface growth, soot mass-nucleation, and soot-oxidation rate increased with an increase in both air temperature and pressure. Finally, the fuel consumption rate showed a decreasing trend with air temperature and an increasing trend with pressure elevation.

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