The Chemistry of Combustion Processes

275 Pages·1983·3.949 MB·English

by  Thompson M. Sloane (Eds.)

ACS SYMPOSIUM SERIES 249
The Chemistry of Combustion
Processes
Thompson M. Sloane, EDITOR
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0 General Motors Research Laboratories
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k- Based on a symposium sponsored by
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21/ the Division of Industrial
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0. and Engineering Chemistry
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American Chemical Society, Washington, D.C. 1984
In The Chemistry of Combustion Processes; Sloane, T.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Library of Congress Cataloging in Publication Data
The chemistry of combustion processes.
(ACS symposium series, ISSN 0097 6156; 249)
Includes bibliographies and indexes.
1. Combustion—Congresses.
I. Sloane, Thompson M., 1945- . II. American
Chemical Society. Division of Industrial and
1 Engineering Chemistry. III. American Chemical
00 Society. Meeting (185th: 1983: Seattle, Wash.)
w IV. Series.
9.f
24 QD516.C537 1984 541.3'61 84-2816
0 ISBN 0 8412-0834 4
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at Copyright © 1984
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PRINTED IN THE UNITED STATES OF AMERICA
In The Chemistry of Combustion Processes; Sloane, T.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
ACS Symposium Series
M. Joan Comstock, Series Editor
Advisory Board
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0
0 Robert Baker Geoffrey D. Parfitt
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9.f U.S. Geological Survey Carnegie Mellon University
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3- Martin L. Gorbaty Theodore Provder
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19 Exxon Research and Engineering Co. Glidden Coatings and Resins
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1/ Herbert D. Kaesz James C. Randall
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10 University of California—Los Angeles Phillips Petroleum Company
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oi: Rudolph J. Marcus Charles N. Satterfield
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3 | Office of Naval Research Massachusetts Institute of Technology
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6, Marvin Margoshes Dennis Schuetzle
pril 1 Technicon Instruments Corporation FoRrde sMearoctohr LCaobmorpaatonryy
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e: Donald E. Moreland
Dat USDA, Agricultural Research Service Davis L. Temple, Jr.
n Mead Johnson
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ati W. H. Norton
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bli J. T. Baker Chemical Company Charles S. Tuesday
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P General Motors Research Laboratory

Robert Ory
USDA, Southern Regional C. Grant Willson
Research Center IBM Research Department
In The Chemistry of Combustion Processes; Sloane, T.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
FOREWORD
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9.f The ACS SYMPOSIUM SERIES was founded in 1974 to provide
24 a medium for publishing symposia quickly in book form. The
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1 IN CHEMISTRY SERIES except that in order to save time the
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1/b papers are not typeset but are reproduced as they are sub­
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0 mitted by the authors in camera-ready form. Papers are re­
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10. viewed under the supervision of the Editors with the assistance
oi: of the Series Advisory Board and are selected to maintain the
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19 previously published papers are not accepted. Both reviews
16, and reports of research are acceptable since symposia may
pril embrace both types of presentation.
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In The Chemistry of Combustion Processes; Sloane, T.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
PREFACE
IN RECENT YEARS, combustion science has undergone a dramatic transfor­
mation as modern analytical tools have been applied to the study of
combustion systems. Techniques involving molecular beams and lasers,
which have been so successful at breaking new ground in the fields of
spectroscopy and chemical reaction kinetics and dynamics, are now yielding
information in increasingly microscopic detail about the physics and chemis­
1
00 try of combustion processes. These new techniques, particularly laser tech­
pr
9. niques, have gone beyond the demonstration stage and have made significant
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02 contributions to our knowledge.
3-
8 This volume focuses on the understanding of chemical aspects of
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k- combustion processes that has been achieved with these new experimental
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1/ methods and with the concurrent increase in theoretical work. The signifi­
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1 cance of these topics in current combustion science is due principally to their
0.
doi: 1 arnodl e sianf ethtye. sFtorro negxlaym lipnlkee, dth aer esausb joecf te noefr dgeyt ocnoantsieornvsa tiiso no,f pporilmluatarny ti mempoisrstiaonncse,
83 | in the transportation safety of natural gas in both the liquid and gaseous
9
6, 1 state. New methods of ignition may yield more efficient combustion pro­
pril 1 cneitsrsoegse inn caountovmerosiboinle teon ngiitnreisc. oAxi dbee ttweril lu anidde irnst arendduincign ogf n tihtrei cc hoxemidies termy iosfs ifounesl
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e: from coal-fired combustors and from combustors utilizing heavy fuels made
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D from coal and shale. A determination of the mechanism of soot formation
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atio and destruction will help to make the highly efficient diesel engine more
blic environmentally acceptable in transportation vehicles and should also aid in
Pu reducing soot emissions from combustors burning coal and heavy liquid

fuels.
I would like to thank the authors and speakers for their contributions
that made this symposium such a worthwhile endeavor. Thanks are also due
to the publishers for providing the means to record the proceedings of this
symposium.
THOMPSON M. SLOANE
General Motors Research Laboratories
Warren, Michigan
December 1983
vu
In The Chemistry of Combustion Processes; Sloane, T.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
1
Role of C Hydrocarbons in Aromatic Species
4
Formation in Aliphatic Flames
J. A. COLE1, J. D. BITTNER2, J. P. LONGWELL, and J. B. HOWARD
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge,
MA 02139
1
0
h0 The free-radical addition reaction expressed as
c
9. 1,3-butadienyl + acetylene --> benzene + H-atom
4
02 is shown to account for benzene formation in the
83- preheat region of a low-pressure, near-sooting,
9
1 premixed 1,3-butadiene flame using an estimated
k-
b rate constant, Log k = 8.5 - 3.7/2.3 RT l/(mol·s),
1/
2 and measured species concentration profiles. Using
0
0.1 similarly estimated rate constants with activation
doi: 1 ethnaetr g1ie,s3 -bouft a1d.i8e,n y0l. 6a, ddanitdio 3n. 7t ok cCa4lH/m2,o lC 4iHt 4,i sa nshdo wn
3 | C3H4 also accounts for the formation of phenylace-
8
9 tylene and styrene but not toluene. Other reaction
1
6, mechanisms involving C-4 hydrocarbons also are con­
1
April stiiodne readn db muto laarre f ltuoxo pslroowf iliens thobist aifnlaemd eb. y Cmoonlceecnutlraar­–
e: beam sampling with on-line mass spectrometry are
Dat presented for 31 species.
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P in flames. The aromatic structure may abet molecular growth lead­

ing to PAH and soot formation through its ability to stabilize
radicals formed from addition of aromatic radicals to unsaturated
aliphatics such as acetylenic species (1*2)· Accordingly, both
aromatics and unsaturated aliphatics would be important for growth
processes. Both types of species are prevalent in the flame zone
where growth occurs. Aromatic structures with unsaturated side
chains also are observed there (1^2) ·
1 Current address: Energy and Environmental Research Corporation, 18 Mason, Irvine, CA
92714
2Current address: Cabot Corporation, Concord Road, Billerica, MA 01821
0097-6156/84/0249-0003506.00/0
© 1984 American Chemical Society
In The Chemistry of Combustion Processes; Sloane, T.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
4 CHEMISTRY OF COMBUSTION PROCESSES
In aliphatic flames aromatic rings must be formed from non-
aromatic precursors, but an accepted mechanism for this critical
step has not appeared in the literature. Attempts to derive mech­
anisms for benzene formation in flames have suffered primarily
from the lack of pertinent kinetic or thermodynamic data. Further­
more, we have found no literature wherein formation rates of ben­
zene, or other aromatics, predicted from a mechanism are compared
with rates measured in a flame.
We will not attempt to review here the many mechanisms which
have been proposed to account for aromatic formation in aliphatic
flames. Suffice it to say that these fall basically into three
categories: ionic mechanisms; concerted, pericyclic mechanisms;
and free radical mechanisms.
The reaction kinetics of different hydrocarbon ions in flames
01 are not sufficiently understood to permit testing of proposed ion-
0
h molecule reactions leading to aromatic formation. This area is of
c
9. interest for further study, especially of growth mechanisms for
4
02 larger aromatic species and soot. With regard to pericyclic mech­
83- anisms such as Diels-Alder reactions, observations made in buta­
9
1 diene flames have led to proposals that butadiene reacting with
k-
b other olefins might be responsible for aromatic formation (4-6).
1/
2 Flame and pyrolysis studies, however, have shown no evidence of
0
0.1 Diels-Alder reactions. As described below, we have compared known
doi: 1 raneda cftoiuonn d rDaiteesl sw-iAthl dmere arseuarcetdi ofnosr mtoa tbieo n trooa tsesl owi n tbou tbae diseineg niffliacmaenst
3 | (7,8).
8
19 Nevertheless, a link between four-carbon species and PAH for­
6, mation would be consistent with the prominence of C-4 hydrocarbons
1
April lin- bfultaemne-s3 -wynhee re( CP4AHH 4;o rv isnoyotl aacreet ybleeinneg) cfoornmceedn.t raItni opn aprrtoifciulleasr , mimic
e: those of benzene and PAH in many fuel-rich flames (9).
at
D In this work the net formation rates of benzene, toluene,
on phenylacetylene, and styrene, and concentrations of possible pre­
ati cursors, were determined as a function of distance from the burner
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bli in the primary reaction zone of a low-pressure, near-sooting 1,3-
u
P butadiene-oxygen-4% argon flame. These rates are compared with

estimated rates for several reaction mechanisms.
Experimental
The apparatus is a low-pressure flat-flame burner with a molecular-
beam sampling instrument having a quartz probe and an on-line quad-
rupole mass-spectrometer (Figure 1). The design features and
measurement techniques are the same as those described elsewhere
(1,10).
A near-sooting laminar premixed flat flame was produced at a
burner chamber pressure of 2.67 kPa (20 torr) with 52.1 normal
cm3 · s"1 (0.1 MPa, 298 K) of feed gas consisting of 29.5 mol%
1,3-butadiene, 67.5 mol% oxygen, and 3.0 mol% argon, corresponding
to a fuel-equivalence ratio, φ, of 2.4 and a cold-gas velocity of
In The Chemistry of Combustion Processes; Sloane, T.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
1. COLE ET AL. C4 Hydrocarbons in Aromatic Species Formation 5
0.5 m·s at 298 Κ. At this pressure and cold-gas velocity the
sooting limit was found at φ « 2.46.
All of the gases used were more than 99% pure and were used
as supplied by the manufacturers.
Individual species were identified by mass and ionization po­
tential. Their mole fractions were measured at the centerline of
the flame as a function of distance from the burner as described
elsewhere (1,10).
Estimated probable errors for species mole fraction are shown
in Table I below. The mole fractions of the largest hydrocarbon
Table 1. Estimated Probable Errors for Species Mole-Fraction
Measurements
1
0
0
h Species Estimated Probable Error
c
9. Major Species + 3%
4
02 H0 + 8%
983- ^22^2 +12%
1 +17%
k- Hydroxyl
b +19%
1/ H-atom
2 +50%
0 Other radicals
0.1 Species larger than Benzene factor of two
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8 species were determined relative to each other with greater accu­
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6, 1 racy than the errors associated with their absolute mole fractions
1 would suggest.
pril The mole fraction profiles were numerically smoothed and dif­
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e: ferentiated in order to determine the species1 molar fluxes. This
at process was repeated on the flux profiles in order to provide net
D
n molar rates of formation or destruction for each species. The
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ati numerical techniques have been described previously (1,2,7,10).
blic Probable errors associated with fluxes and reaction rates so de­
u termined cannot be stated explicitly because the perturbation of
P
the sampling probe on the one-dimensional flame assumption has not
been assessed quantitatively.
Nevertheless, the overall accuracy suggested by element bal­
ances is encouraging. The calculated total-carbon mass flux agrees
to within 30% throughout the flame with the value determined from
the measured fuel feedrate. The agreement is to within 5% in the
region of the flame considered in this work.
The gas temperature profiles used for this analysis were cal­
culated from the assumption of equilibrium in the reaction
H- + H0 % H + OH (1)
2 2
This reaction appears to be equilibrated beyond the primary reac­
tion zone (region of total fuel and/or oxygen consumption) in this
In The Chemistry of Combustion Processes; Sloane, T.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
6 CHEMISTRY OF COMBUSTION PROCESSES
flame and elsewhere (11). The temperature was calculated by com­
paring the equilibrium equation
_ XH XH0
v 9
XH X0H
2
with the known standard Gibbs energy charge,Δ G°, for Reaction (1)
as a function of temperature (12). In this case the equilibrium
constant, K, is related to ÙG° by
AG° = -RT In Κ
The resulting temperature profile is shown in Figure 2. The temp­
erature in the primary reaction zone was estimated by linear ex­
1 trapolation to 300 Κ at the burner. Propagation of error calcula­
0
h0 tions suggests a maximum probable error of +150 K.
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4
02 Experimental Results and Discussion
3-
8
9
1 The mole-fraction and molar-flux profiles obtained for 31 species
k-
b are shown in Figures 3-8. Inspection of the flux profiles in
1/
2 Figure 3 reveals little evidence of reaction up to about 5 mm from
0
0.1 the burner. Butadiene is consumed in the region 5-10 mm, although
doi: 1 pdroiesm anroitl y bebecyoomend no7 tmimc ab(lFei guunrte il 3)a. bouOtx y8g.e5 n mcm on(sFuimgputrieo n4,) haonwd evperro,­
83 | duction of CO, 002, and H20 occurs later still (Figures 3 and 5).
9 Nevertheless some oxidation occurs prior to 8.5 mm as is evidenced
1
6, by the fluxes of the oxygenated species in Figure 4. The species
1
April Ca3tHt4aOck aonnd bCu4tHa5dOi epnreo baanbdl y alrieèsnuel t (1f3r,o1m 4)t.r ipTlhete re(fgorroeu nd0 -sattaotm e)m ay0 -aptloamy
e: a role in butadiene destruction. Such behavior would be consistent
Dat with the observation that the fractional decomposition rate (s~l) of
on butadiene at the 1120 Κ position in this flame, where 0 atoms are
ati available by diffusion from the oxidation zone, is significantly
c
ubli larger than that measured in the presence of 02 at 1120 Κ in an
P approximately isothermal flow reactor (15).

Hydrocarbon species with one, two, or three carbon atoms are
represented in Figure 6; those with four carbon atoms in Figure 7.
The behavior and position of the C4H4 mole fraction profile (Fig­
ure 7) are strikingly similar to those of a ll the aromatic species
shown in Figure 8. In contrast, the profiles of diacetylene
(C4H2, Figure 7) and the polyacetylenes (CH and CH, Figure 8)
6 2 g 2
are similar to those of acetylene (Figure 6).
Figure 8 shows that benzene and the other single-ring aromat-
ics whose formation rates are studied here are formed mainly in the
region of butadiene consumption. Their maximum net rates of form­
ation occur prior to 9.5 mm. Since significant 0 consumption
2
begins at 8.5 mm and oxidation is evident prior to that, the ques­
tion arises as to whether oxidative consumption of aromatics con­
tributes significantly to their net reaction rates in the region
of interest here
In The Chemistry of Combustion Processes; Sloane, T.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
1. COLE ET AL. C4 Hydrocarbons in Aromatic Species Formation
ELECTRON
MULTIPLIER
OUADRUPOLE MASS
FILTER 4 INCH
DIFFUSION
IONIZER
PUMP
LN-COOLED
2
WALLS COLLIMATOR
TUNING FORK
CHOPPER
6 INCH
CALIBRATION GAS — DIFFUSION
PUMP
EFFUSIVE
SOURCE
1
0
0
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4 -I— SKIMMER
2
0
83- QUARTZ PROBE
9
1
bk- BURNER
1/
2
0
1
0.
doi: 1 6 INCH MVEACCHUAUNMI CPAULM P
3 | DIFFUSION
8 PUMP
19 • PREMIXED GASES
6,
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pril
A Figure 1. Molecular beam mass spectrometer flame sampling
e: apparatus.
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I 1 LU 1 .—: 1
Ο 10 20 30 40
HEIGHT ABOVE BURNER (mm)
Figure 2. Temperature profile in near-sooting. Points, calculated
assuming equilibration of H + E^O zz£ OH + Η ·, and curve, estimated
and used in data analysis and mechanism predictions. Conditions:
0= 2Λ; C^Hg/0/3.0#Ar flame; cold gas velocity = 0.5 m/s ; and
2
pressure = 2.67 kPa.
In The Chemistry of Combustion Processes; Sloane, T.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1983.