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Title: Effect of partial premixing on the sooting structure of methane flames

Abstract

An experimental investigation of the sooting structure of diluted methane-oxygen counterflow flames is reported for partial premixing in the following two nonpremixed flame configurations: Case 1: Nonpremixed flame on the oxidizer side of the stagnation plane, Case 2: Nonpremixed flame on the fuel side of the stagnation plane. Effects of both fuel-side and oxidizer-side partial premixing for Cases 1 and 2 were investigated in a low-strain-rate ({approx}6-8 s{sup -1}) counterflow flame. Computations using OPPDIF code were in excellent agreement with the measured concentrations of major species and [OH]. Distribution of measured soot volume fraction and particle sizes are presented along with measured distributions of C{sub 2} hydrocarbon species. Soot loading can increase or decrease depending on (a) the level of partial premixing, (b) the side of partial premixing (fuel side or oxidizer side), and (c) the nonpremixed flame configuration. Of particular interest is the trend for fuel-side partial premixing of Case 1, where the peak soot loading, the peak soot particle diameter, and the thickness of the soot zone initially decrease and then increase with progressive partial premixing. The trends presented are discussed based on chemical, dilution, and flow-field effects of partial premixing on soot growth in counterflow flames. Unlikemore » previous literature, which focused on soot inception, this work emphasizes the role of partial premixing on soot growth by taking into account the changes in the temperature-time history of soot particulates in addition to the previously reported 'chemical' and 'dilution' effects.« less

Authors:
;  [1]
  1. Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2125 (United States)
Publication Date:
OSTI Identifier:
20685996
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 144; Journal Issue: 1-2; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 03 NATURAL GAS; METHANE; OXYGEN; FLAMES; SOOT; MIXING; COUNTER CURRENT; PARTICLE SIZE

Citation Formats

Mungekar, Hemant P., and Atreya, Arvind. Effect of partial premixing on the sooting structure of methane flames. United States: N. p., 2006. Web. doi:10.1016/j.combustflame.2005.08.007.
Mungekar, Hemant P., & Atreya, Arvind. Effect of partial premixing on the sooting structure of methane flames. United States. doi:10.1016/j.combustflame.2005.08.007.
Mungekar, Hemant P., and Atreya, Arvind. Sun . "Effect of partial premixing on the sooting structure of methane flames". United States. doi:10.1016/j.combustflame.2005.08.007.
@article{osti_20685996,
title = {Effect of partial premixing on the sooting structure of methane flames},
author = {Mungekar, Hemant P. and Atreya, Arvind},
abstractNote = {An experimental investigation of the sooting structure of diluted methane-oxygen counterflow flames is reported for partial premixing in the following two nonpremixed flame configurations: Case 1: Nonpremixed flame on the oxidizer side of the stagnation plane, Case 2: Nonpremixed flame on the fuel side of the stagnation plane. Effects of both fuel-side and oxidizer-side partial premixing for Cases 1 and 2 were investigated in a low-strain-rate ({approx}6-8 s{sup -1}) counterflow flame. Computations using OPPDIF code were in excellent agreement with the measured concentrations of major species and [OH]. Distribution of measured soot volume fraction and particle sizes are presented along with measured distributions of C{sub 2} hydrocarbon species. Soot loading can increase or decrease depending on (a) the level of partial premixing, (b) the side of partial premixing (fuel side or oxidizer side), and (c) the nonpremixed flame configuration. Of particular interest is the trend for fuel-side partial premixing of Case 1, where the peak soot loading, the peak soot particle diameter, and the thickness of the soot zone initially decrease and then increase with progressive partial premixing. The trends presented are discussed based on chemical, dilution, and flow-field effects of partial premixing on soot growth in counterflow flames. Unlike previous literature, which focused on soot inception, this work emphasizes the role of partial premixing on soot growth by taking into account the changes in the temperature-time history of soot particulates in addition to the previously reported 'chemical' and 'dilution' effects.},
doi = {10.1016/j.combustflame.2005.08.007},
journal = {Combustion and Flame},
number = 1-2,
volume = 144,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • Measurement of NO[sub x] emission indices, flame radiant fractions, and visible flame length were made for turbulent, nonpremixed, jet flames for which various amounts of inert diluent or air were mixed with the fuel. The objective of the study was to explore further the role of flame radiation in NO[sub x] production in jet flames. Four fuels, CH[sub 4], C[sub 2]H[sub 4], C[sub 3]H[sub 8], and a 95% CO/5% H[sub 2] mixture (by mass); three inert diluents, N[sub 2], Ar, and CO[sub 2]; and air premixing were employed in parametric tests. Complementary dilution experiments were run with laminar jet flamesmore » using the three hydrocarbon fuels and N[sub 2]. For the turbulent flames, the results showed that the effects of dilution and premixing were strongly dependent on fuel type. Flame temperatures and NO[sub x] emissions increased when the more sooting fuels (C[sub 3]H[sub 8] and C[sub 2]H[sub 4]) were diluted or partially premixed, resulting in increased NO[sub x] emissions. The opposite trend was observed for the nonluminous CO/H[sub 2] flames. Using the results reported here and from Part I. of this study, the effects of residence time, flame temperature, and departure from equilibrium on NO[sub x] emissions, regardless of what parameter affected the change, were well characterized by regressing characteristic NO[sub x] production rates as a function of nonadiabatic characteristic flame temperatures and global residence times. Separate regressions for the hydrocarbon and CO/H[sub 2] flames showed a weaker dependence of NO[sub x] on temperature for the hydrocarbons, suggesting that the prompt NO mechanism is quite active in these flames.« less
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  • Fully closed multiple mapping conditioning (MMC) is used to model partially premixed flames in homogeneous, isotropic decaying turbulence where the partial premixing is caused by local extinction and reignition phenomena. Two reference variables that represent mixing and reaction progress, such as mixture fraction and sensible enthalpy, are used to emulate turbulent scalar fluctuations. Local extinction is achieved by a priori coupling between scalar dissipation and temperature fluctuations via a correlation function that is based on the conditionally averaged sensible enthalpy at stoichiometric composition. The proposed model provides closures for the joint PDF of mixture fraction and sensible enthalpy, for themore » conditional variance equation of a reactive scalar, and for the doubly conditioned dissipation terms. Model results are compared with DNS in three flame cases with varying levels of local extinction, up to global extinction. The joint PDF predicted by MMC is in fair agreement with DNS. It constitutes, however, a clear improvement over conventional models using preassumed distribution functions for the PDFs. The doubly conditioned dissipation terms are modeled well and the results for all major chemical species are in good agreement with DNS. Predictions for intermediate species are also satisfactory. (author)« less
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