Scalar profiles and NO formation in laminar opposed-flow partially premixed methane/air flames
TL;DR: In this article, the authors used Raman scattering and laser-induced fluorescence to measure temperature, the major species (N2, O2, CH4, CO2, H2O, CO, and H2), OH, and NO in steady laminar opposed-flow partially premixed flames of methane and air.
About: This article is published in Combustion and Flame.The article was published on 2001-11-01. It has received 495 citations till now. The article focuses on the topics: Premixed flame & Laminar flow.
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01 Jan 2002
TL;DR: In this paper, an experiment and numerical investigation of a lifted turbulent H2/N2 jet flame in a coflow of hot, vitiated gases is presented, where two combustion models (PDF: joint scalar Probability Density Function and EDC: Eddy Dissipation Concept) are used in conjunction with various turbulence models to predict the lift-off height.
Abstract: An experiment and numerical investigation is presented of a lifted turbulent H2/N2 jet flame in a coflow of hot, vitiated gases. The vitiated coflow burner emulates the coupling of turbulent mixing and chemical kinetics exemplary of the reacting flow in the recirculation region of advanced combustors. It also simplifies numerical investigation of this coupled problem by removing the complexity of recirculating flow. Scalar measurements are reported for a lifted turbulent jet flame of H2/N2 (Re = 23,600, H/d = 10) in a coflow of hot combustion products from a lean H2/Air flame ((empty set) = 0.25, T = 1,045 K). The combination of Rayleigh scattering, Raman scattering, and laser-induced fluorescence is used to obtain simultaneous measurements of temperature and concentrations of the major species, OH, and NO. The data attest to the success of the experimental design in providing a uniform vitiated coflow throughout the entire test region. Two combustion models (PDF: joint scalar Probability Density Function and EDC: Eddy Dissipation Concept) are used in conjunction with various turbulence models to predict the lift-off height (H(sub PDF)/d = 7,H(sub EDC)/d = 8.5). Kalghatgi's classic phenomenological theory, which is based on scaling arguments, yields a reasonably accurate prediction (H(sub K)/d = 11.4) of the lift-off height for the present flame. The vitiated coflow admits the possibility of auto-ignition of mixed fluid, and the success of the present parabolic implementation of the PDF model in predicting a stable lifted flame is attributable to such ignition. The measurements indicate a thickened turbulent reaction zone at the flame base. Experimental results and numerical investigations support the plausibility of turbulent premixed flame propagation by small scale (on the order of the flame thickness) recirculation and mixing of hot products into reactants and subsequent rapid ignition of the mixture.
345 citations
TL;DR: A review of flammability characteristics of hydrogen can be found in this paper, where the authors present a thorough and self-contained tutorial that covers the existing fundamental knowledge in a uniform and concise manner.
297 citations
TL;DR: In this paper, a large-eddy simulation (LES) is applied to a realistic gas turbine combustion chamber configuration where pure methane is injected through multiple holes in a cone-shaped burner.
Abstract: Nitric oxide formation in gas turbine combustion depends on four key factors: flame stabilization, heat transfer, fuel–air mixing and combustion instability. The design of modern gas turbine burners requires delicate compromises between fuel efficiency, emissions of oxides of nitrogen (NOx) and combustion stability. Burner designs allowing substantial NOx reduction are often prone to combustion oscillations. These oscillations also change the NOx fields. Being able to predict not only the main species field in a burner but also the pollutant and the oscillation levels is now a major challenge for combustion modelling. This must include a realistic treatment of unsteady acoustic phenomena (which create instabilities) and also of heat transfer mechanisms (convection and radiation) which control NOx generation.In this work, large-eddy simulation (LES) is applied to a realistic gas turbine combustion chamber configuration where pure methane is injected through multiple holes in a cone-shaped burner. In addition to a non-reactive simulation, this article presents three reactive simulations and compares them to experimental results. The first reactive simulation neglects effects of cooling air on flame stabilization and heat losses by radiation and convection. The second reactive simulation shows how cooling air and heat transfer affect nitric oxide emissions. Finally, the third reactive simulation shows the effects of combustion instability on nitric oxide emissions. Additionally, the combustion instability is analysed in detail, including the evaluation of the terms in the acoustic energy equation and the identification of the mechanism driving the oscillation.Results confirm that LES of gas turbine combustion requires not only an accurate chemical scheme and realistic heat transfer models but also a proper description of the acoustics in order to predict nitric oxide emissions and pressure oscillation levels simultaneously.
287 citations
Cites background from "Scalar profiles and NO formation in..."
...…the cold surroundings (usually the chamber walls) have a constant temperature Ts , the radiative heat loss per unit volume Qr can be calculated (Barlow et al. 2001): Qr = 4σ ( T 4 − T 4s ) ∑ i (piap,i) (2.9) where σ = 5.669 × 10−8 Wm−2 K−4 is the Stefan–Boltzmann constant, T is the local gas…...
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...Assuming that the gases are optically thin and that the cold surroundings (usually the chamber walls) have a constant temperature Ts , the radiative heat loss per unit volume Qr can be calculated (Barlow et al. 2001): Qr = 4σ ( T 4 − T 4 s ) ∑...
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...Re-absorption and inhomogeneous wall temperatures are neglected (Barlow et al. 2001)....
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TL;DR: In this paper, a vitiated coflow flame consisting of a lifted jet flame formed by a fuel jet issuing from a central nozzle into a large coaxial flow of hot combustion products from a lean premixed H 2 /air flame is presented and compared to numerical results from probability density function (PDF) calculations incorporating various mixing models.
280 citations
TL;DR: In this article, a model for the prediction of the nitric oxide (NO) formation in turbulent non-premixed flames is proposed, which is applied to a large-eddy simulation (LES) of Sandia flame D, and the importance of the interaction between turbulence and radiation on temperature and mixture fraction is investigated.
Abstract: A model for the prediction of the nitric oxide (NO) formation in turbulent nonpremixed flames is proposed. Since the NO formation has a strong temperature sensitivity, the accurate prediction of the flame temperature under the consideration of radiative heat losses is required. The first part of the paper addresses the extension of a flamelet-based combustion model to account for radiative heat loss effects by introducing enthalpy as an additional parameter. A transport equation for enthalpy is solved, and the radiative sink term in this equation is obtained from unsteady flamelet solutions. The model is applied to a large-eddy simulation (LES) of Sandia flame D, and the importance of the interaction between turbulence and radiation on temperature and mixture fraction is investigated. Based on the radiative flamelet formulation, a consistent model for the prediction of NO formation is developed in the second part of the paper. In this model, an additional transport equation for the NO mass fraction is sol...
257 citations
References
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TL;DR: In this article, a four-step mechanism for the combustion of methane in air in non-premixed flames is obtained by making steady-state and partial equilibrium approximations for minor species.
754 citations
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11 Sep 2018
367 citations
"Scalar profiles and NO formation in..." refers methods in this paper
...Fig. 5. Temperature dependence of the Planck mean absorption coefficients for CO2 ,H 2O, CH4, and CO determined using RADCAL [ 25 ]....
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...Curve Fitsa for Planck Mean Absorption Coefficients [1, 25 ]...
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...The effect of the Tb term on calculated flame profiles is negligible, so that there is no practical difference between Eq. (2) and the emissiononly formulation, which excludes Tb. Planck mean absorption coefficients for CO2 ,H 2O, CH4, and CO were calculated using RADCAL [ 25 ] and expressed as polynomials in temperature....
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TL;DR: In this article, single-shot Raman, Rayleigh, and laser-induced fluorescence (LIF) measurements have been performed simultaneously in a turbulent jet flame (Re = 15,200) in order to determine joint probability density functions of temperature, mixture fraction, major species (CH4, H2, O2, N2, H 2O, CO2, CO), and minor species (OH, NO) mass fractions.
218 citations
TL;DR: In this paper, a two-stage counterflow methane-air flames at normal atmospheric pressure and a feed-stream temperature of about 300 K were measured and computations were made of structures of two stage counter-flow methane air flames, including formation of species containing two carbon atoms.
196 citations
TL;DR: In this article, a combination of Raman-Rayleigh scattering and laser-induced fluorescence was used to obtain nonintrusive measurements of temperature, major species, CO, OH, and NO in an atmospheric pressure, laminar methane-air Bunsen flame, and they found that the inner unburned fuel-air mixture experiences significant preheating as it travels up into the conical flame zone surrounding it.
144 citations