Flame structure and thermal NOx formation in hydrogen diffusion flames with reduced kinetic mechanisms

KSME Journal ◽  
1995 ◽  
Vol 9 (3) ◽  
pp. 377-384 ◽  
Author(s):  
Su-Ryong Lee ◽  
Sim-Soo Park ◽  
Suk-Ho Chung
Keyword(s):  
Hydrogen Diffusion ◽  
Diffusion Flames ◽  
Flame Structure ◽  
Nox Formation ◽  
Kinetic Mechanisms ◽  
Thermal Nox

Numerical Modeling of Pollution Formation in Waste-to-Energy Systems Using Computational Fluid Dynamics

2011 ◽  
Author(s):  
Alex Frank ◽  
Marco J. Castaldi ◽  
Masato R. Nakamura
Keyword(s):  
Fluid Dynamics ◽  
Gas Phase ◽  
Energy Systems ◽  
Waste To Energy ◽  
High Fidelity ◽  
Nox Formation ◽  
Pollutant Formation ◽  
Kinetic Mechanisms ◽  
Thermal Nox ◽  
Fidelity Model

This investigation has been undertaken to better understand pollutant formation in Waste-to-Energy (WTE) systems by using Computation Fluid Dynamics (CFD). An above-grate gas phase only model was built and calculated in FLUENT™ with the intent of specifically studying the factors that influence the formation of NOx. Results are shown for a typical reciprocating-grate WTE boiler operating on municipal solid waste (MSW). Contours of velocity, temperature, CO2, CO, H2O, and O2 agree well with previous modeling and data resulting in a high fidelity model that can be implemented in the next phase of this research. Preliminary data is shown for thermal NOx and the results are promising. The next phase of this research will include the development and implementation of detailed kinetic mechanisms (DKM) to model NOx formation with the current boiler presented as well as others with varying fuels.

scholarly journals The Effect of Variable Air–Fuel Ratio on Thermal NOx Emissions and Numerical Flow Stability in Rotary Kilns Using Non-Premixed Combustion

Processes ◽  
2021 ◽  
Vol 9 (10) ◽  
pp. 1723
Author(s):  
Mohamed el Abbassi ◽  
Domenico Lahaye ◽  
Cornelis Vuik
Keyword(s):  
Wall Temperature ◽  
Diffusion Flames ◽  
Three Dimensional ◽  
Nox Emissions ◽  
Unstable Flow ◽  
Nox Formation ◽  
Fuel Ratio ◽  
Rotary Kilns ◽  
Thermal Nox ◽  
The Impact

One of the quickest ways to influence both the wall temperature and thermal NOx emissions in rotary kilns is to change the air–fuel ratio (AFR). The normalized counterpart of the AFR, the equivalence ratio, is usually associated with premixed flames and studies of its influence on diffusion flames are inconsistent, depending on the application. In this paper, the influence of the AFR is investigated numerically for rotary kilns by conducting steady-state simulations. We first conduct three-dimensional simulations where we encounter statistically unstable flow at high inflow conditions, which may be caused by vortex stretching. As vortex stretching vanishes in two-dimensional flow, the 2D simulations no longer encounter convergence problems. The impact of this simplification is shown to be acceptable for the thermal behaviour. It is shown that both the wall temperature and thermal NOx emissions peak at the fuel-rich and fuel-lean side of the stoichiometric AFR, respectively. If the AFR continues to increase, the wall temperature decreases significantly and thermal NOx emissions drop dramatically. The NOx validation, however, shows different results and indicates that the simulation model is simplified too much, as the measured NOx formation peaks at significantly fuel-lean conditions.

Reduction of NOx Formation by Water Sprays in Strained Two-Stage Flames

1997 ◽  
Vol 119 (4) ◽  
pp. 836-843 ◽  
Author(s):  
S. C. Li ◽  
N. Ilincic ◽  
F. A. Williams
Keyword(s):  
Diffusion Flames ◽  
Laser Sheet ◽  
Flame Structure ◽  
Flame Temperature ◽  
Temperature Fields ◽  
Two Stage ◽  
Two Phase ◽  
Nox Formation ◽  
Numerical Predictions ◽  
Water Sprays

Staged combustion can be employed to reduce the formation of CO and NOx, stabilize the flame, decrease the flame temperature, and create better working conditions in gas turbine combustors. To help understand influences of partial premixing and addition of water on NOx formation, we study two-stage flames in a counterflow spray burner. This paper reports experimental and theoretical results concerning two-stage combustion in which one feed stream is composed of a fuel-rich mixture of methane and air and the other is air. Water sprays are added to the air stream. This two-phase laminar counterflow configuration exhibits a green premixed flame, a blue diffusion flame, and a vaporization plane. All three are flat and parallel. The separation distances between them decrease with increasing equivalence ratio and strain rate. Flow visualization is provided through illumination by an argon ion laser sheet, velocity fields and spray structure are measured by a phase-doppler particle analyzer, concentration fields of major stable species are measured by gas chromatography of samples withdrawn from the flame, and temperature fields are measured by a thermocouple. Numerical integrations that employ a recent chemical-kinetic data base are performed to model the flame structure and NOx formation. Comparisons of experimental results with numerical predictions are made to test agreement. This work provides information on hydrocarbon combustion in both premixed flames and diffusion flames, indicates how NOx is formed in fuel-rich flames, and suggests how the pollutants can be reduced.

scholarly journals A Numerical Investigation of NOx Formation in Counterflow CH4/H2/Air Diffusion Flames

2006 ◽  
Author(s):  
Hongsheng Guo ◽  
Stuart W. Neill ◽  
Gregory J. Smallwood
Keyword(s):  
Diffusion Flames ◽  
Numerical Study ◽  
Flame Structure ◽  
Pure Hydrogen ◽  
No Emission ◽  
Nox Formation ◽  
No Formation ◽  
Hydrogen Enrichment ◽  
Air Diffusion ◽  
Emission Index

A detailed numerical study was carried out for the effect of hydrogen enrichment on flame structure and NOx formation in counterflow CH4/air diffusion flames. Detailed chemistry and complex thermal and transport properties were employed. The enrichment fraction was changed from 0 (pure CH4) to 1.0 (pure H2). The result indicates that for flames with low to moderate stretch rates, with the increase of the enrichment fraction from 0 to 0.5~0.6, NO emission index keeps almost constant or only slightly increases. When the enrichment fraction is increased from 0.5~0.6 to about 0.9, NO emission index quickly increases, and finally NO formation decreases again when pure hydrogen flame condition is approached. However, for flames with higher stretch rates, with the increase of hydrogen enrichment fraction from 0 to 1.0, the formation of NO first quickly increases, then slightly decreases and finally increases again. Detailed analysis suggests that the variation of the characteristics in NO formation in stretched CH4/air diffusion flames is caused by the change of flame structure and NO formation mechanism, when the enrichment fraction and stretch rate are changed.

scholarly journals Reduction of NOx Formation by Water Sprays in Strained Two-Stage Flames

1996 ◽  
Author(s):  
S. C. Li ◽  
N. Ilincic ◽  
F. A. Williams
Keyword(s):  
Diffusion Flames ◽  
Laser Sheet ◽  
Flame Structure ◽  
Flame Temperature ◽  
Temperature Fields ◽  
Two Stage ◽  
Two Phase ◽  
Nox Formation ◽  
Numerical Predictions ◽  
Water Sprays

Staged combustion can be employed to reduce the formation of CO and NOx, stabilize the flame, decrease the flame temperature and create better working conditions in gas turbine combustors. To help understand influences of partial premixing and addition of water on NOx formation, we study two-stage flames in a counterflow spray burner. This paper reports experimental and theoretical results concerning two-stage combustion in which one feed stream is composed of a fuel-rich mixture of methane and air and the other is air. Water sprays are added to the air stream. This two-phase laminar counterflow configuration exhibits a green premixed flame, a blue diffusion flame and a vaporization plane. All three are flat and parallel. The separation distances between them decrease with increasing equivalence ratio and strain rate. Flow visualization is provided through illumination by an argon ion laser sheet, velocity fields and spray structure are measured by a phase-doppler particle analyzer, concentration fields of major stable species are measured by gas chromatography of samples withdrawn from the flame, and temperature fields are measured by a thermocouple. Numerical integrations which employ a recent chemical-kinetic data base are performed to model the flame structure and NOx formation. Comparisons of experimental results with numerical predictions are made to test agreement. This work provides information on hydrocarbon combustion in both premixed flames and diffusion flames, indicates how NOx is formed in fuel-rich flames and suggests how the pollutants can be reduced.

scholarly journals 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 ◽  
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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