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Title: A new flame sheet model to reflect the influence of the oxidation of CO on the combustion of a carbon particle

Abstract

A model with a moving flame front is proposed for the combustion of a carbon particle, taking into account the effect of CO oxidizing in the boundary layer around the particle. Using this model, the continuous transition of the effective combustion product from CO{sub 2} under the ignition condition to CO under the condition of diffusion control has been successfully realized. Good agreement was obtained with the experimental measurements of Young and Niksa; such agreement could not be obtained using the customary single-film model.

Authors:
;  [1];  [2]
  1. Institute of Thermal Energy Engineering, Shanghai Jiaotong University, Shanghai 200240 (China)
  2. Department of Thermal Energy Engineering, Tsinghua University, Beijing 100084 (China)
Publication Date:
OSTI Identifier:
20677726
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 143; Journal Issue: 3; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 01 COAL, LIGNITE, AND PEAT; COMBUSTION; CARBON; CARBON MONOXIDE; COMBUSTION KINETICS; BOUNDARY LAYERS; OXIDATION; MATHEMATICAL MODELS; FLAME PROPAGATION

Citation Formats

Zhang, Mingchuan, Yu, Juan, and Xu, Xuchang. A new flame sheet model to reflect the influence of the oxidation of CO on the combustion of a carbon particle. United States: N. p., 2005. Web. doi:10.1016/j.combustflame.2005.05.010.
Zhang, Mingchuan, Yu, Juan, & Xu, Xuchang. A new flame sheet model to reflect the influence of the oxidation of CO on the combustion of a carbon particle. United States. doi:10.1016/j.combustflame.2005.05.010.
Zhang, Mingchuan, Yu, Juan, and Xu, Xuchang. Tue . "A new flame sheet model to reflect the influence of the oxidation of CO on the combustion of a carbon particle". United States. doi:10.1016/j.combustflame.2005.05.010.
@article{osti_20677726,
title = {A new flame sheet model to reflect the influence of the oxidation of CO on the combustion of a carbon particle},
author = {Zhang, Mingchuan and Yu, Juan and Xu, Xuchang},
abstractNote = {A model with a moving flame front is proposed for the combustion of a carbon particle, taking into account the effect of CO oxidizing in the boundary layer around the particle. Using this model, the continuous transition of the effective combustion product from CO{sub 2} under the ignition condition to CO under the condition of diffusion control has been successfully realized. Good agreement was obtained with the experimental measurements of Young and Niksa; such agreement could not be obtained using the customary single-film model.},
doi = {10.1016/j.combustflame.2005.05.010},
journal = {Combustion and Flame},
number = 3,
volume = 143,
place = {United States},
year = {Tue Nov 01 00:00:00 EST 2005},
month = {Tue Nov 01 00:00:00 EST 2005}
}
  • The behavior of the combustion rate of carbon, when the flame sheet attaches to or collapses at the carbon surface, is studied in a model in which the heterogeneous reactions 2C{sub (s)} + O{sub 2} {r{underscore}arrow} 2CO[reaction (I)] and C{sub (s)} + CO{sub 2} {r{underscore}arrow} 2CO[(IV)] and the homogeneous reaction 2CO + O{sub 2} {r{underscore}arrow} 2CO{sub 2}[(III)] occur in a stagnation flow of air. In this model the surface mass fraction of CO{sub 2} increases with an increase in the combustion rate. In a restricted case in which the heterogeneous reaction is solely (IV), CO{sub 2} is on the onemore » hand the product of an overall surface reaction [reaction (III) plus (IV)] but on the other hand the reactant of reaction (IV) which determines the rate of this overall reaction. This causes peculiar variations of the combustion rate: (1) the combustion rate vanishes at a nonvanishing D{sub s(IV)}(D{sub 2(n)} is the surface Damkoehler number of the nth reaction); (2) the combustion rate varies dramatically with D{sub s(IV)} in the D{sub s(IV)} range in which the combustion rate is nonvanishing. When reaction (I) occurs at all, CO{sub 2} is made from CO by reaction (III); therefore, reaction (IV) occurs even in the D{sub s(IV)} range in which this reaction never occurs by itself. When D{sub s(IV)} is kept constant and D{sub s(I)} is increased, the combustion rate and the contribution of the gasification of carbon by reaction (I) naturally increase, but, because of an increase in the surface mass fraction of CO{sub 2} with increasing combustion rate, the contribution by reaction (IV) also increases.« less
  • The attachment of the flame sheet to the carbon surface is studied in a carbon combustion model where the heterogeneous reactions 2C{sub (s)} + O{sub 2} {yields} 2CO and C{sub (s)} + CO{sub 2} {yields} 2CO and the homogeneous reaction 2CO + O{sub 2} {yields} 2CO{sub 2} occur in a stagnation flow field. When the flame sheet attaches to the carbon surface, the governing equations become homogeneous. The surface constraining conditions for each species must be built, taking into account the consumption or production of the species not only by the heterogeneous reactions but also by the homogeneous reaction occurringmore » at the carbon surface. The rebuilt surface constraining conditions differ from the conditions to be imposed when the flame sheet forms away from the carbon surface. The field becomes identical with that of a model where only the heterogeneous reaction C{sub (s)} + O{sub 2} {yields} CO{sub 2} takes place.« less
  • Acetone ignition delay and stretch-free laminar flame speed measurements have been carried out and a kinetic model has been developed to simulate these and literature data for acetone and for ketene, which was found to be an important intermediate in its oxidation. The mechanism has been based on one originally devised for dimethyl ether and modified through validation of the hydrogen, carbon monoxide and methane sub-mechanisms. Acetone oxidation in argon was studied behind reflected shock waves in the temperature range 1340-1930 K, at 1 atm and at equivalence ratios of 0.5, 1 and 2; it is also shown that themore » addition of up to 15% acetone to a stoichiometric n-heptane mixture has no effect on the measured ignition delay times. Flame speeds at 298 K and 1 atm of pure acetone in air were measured in a spherical bomb; a maximum flame speed of {proportional_to}35 cm s{sup -1} at {phi}=1.15 is indicated. (author)« less
  • An analysis is made of a model in which the heterogeneous reaction is 2C/sub (s)/ + O/sub 2/ ..-->.. 2CO and the CO produced thereby undergoes the homogeneous reaction 2CO + O/sub 2/ ..-->.. 2CO/sub 2/; the homogeneous reaction interferes with the heterogeneous reaction through the consumption of O/sub 2/. Constant density and unity Lewis number of the gas mixture are assumed. Self-similarity of the flow is also assumed, and the analysis is reduced to a problem of solving an ordinary differential equation for energy conservation. The effects of the surface Damkohler number D/sub s/, the gas-phase Damkohler number D/submore » g/, and the dimensionless surface temperature T/sub w//sup --/ on the dimensionless combustion rate -f/sub w/ are investigated. When D/sub g/ = O or D/sub g/ ..-->.. infinity, the solution can be obtained from degenerate governing equations; -f/sub w/ is independent of T/sub w/, and simple relations hold between D/sub s/ and -f/sub w/. The solution for D/sub g/ ..-->.. infinity exhibits singularity at the carbon surface. When neither D/sub g/ = O nor D/sub g/ ..-->.., infinity the variations of -f/sub w/(D/sub s/), -f/sub w/(D/sub g/), and -f/sub w/(T/sub w//sup --/) are determined numerically for the ranges of D/sub s/ (0.001-100), D/sub g/(10/sup 2/-10/sup 14/), and T/sub w//sup --/ (0.15-0.40). It is found that (1) a sharp gas-phase reaction zone located away from the surface does not form, (2) -f/sub w/ increases with increasing D/sub s/ for any value of D/sub g/ and T/sub w//sup --/, (3) at a given D/sub s/, -f/sub w/ decreases with increasing D/sub g/ for any value of T/sub w//sup ..-->../-how -f/sub w/ decreases with increasing log D/sub g/ is roughly the same for all the values of T/sub w//sup --/, (4) at a given D/sub s/, -f/sub w/ decreases with increasing T/sub w//sup --/ for any value of D/sub g/-how -f/sub w/ decreases with increasing T/sub w//sup --/ differs greatly with the value of D/sub g/.« less