United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/048 Jan. 1986
&EPA Project Summary
Fundamental Combustion
Research Applied to Pollution
Formation Volume I.
FCR Program Overview and
Gas-Phase Chemistry
W. R. Seeker, M. P. Heap, T. J. Tyson, J. C. Kramlich, and T. L Corley
This volume (Volume I) is an
overview of the entire contract and the
summary of the technical effort in gas-
phase chemistry.
EPA's first fundamental combustion
research (FCR) applied to pollution con-
trol program was a subcontract ori-
ented program focused on the simulta-
neous control of nitrogen oxides (NOX)
and participate from large, confined,
1-atmosphere, turbulent diffusion
flames burning heavy residual oil and
pulverized coal. The program had three
major objectives:
• To generate the understanding of
combustor behavior necessary to
aid EPA/AEERL's Combustion Re-
search Branch (CRB) in developing
control strategies to minimize NOX
emissions from stationary sources.
• To develop engineering models
which would allow effective uti-
lization of a large body of funda-
mental information in the develop-
ment of new NOX control
techniques.
• To identify critical information nec-
essary for low NOX combustor de-
velopment and to generate it in a
time frame which was consistent
with the needs of the CRB technol-
ogy development programs.
The FCR program was divided into
three program areas and two support
areas. The major program areas were
concerned with (1) gas-phase chem-
istry, (2) the physics and chemistry of
two-phase systems, and (3) transport
processes in reacting systems. This or-
ganization was designed to address the
critical phenomena that occurred to
solid or liquid fuels in turbulent diffu-
sion flames in order to describe fuel NO
formation from stationary sources. The
two support areas were for the devel-
opment of measurement techniques
and the development of analytical tools
required during the program and for fu-
ture investigations. Table 1 lists the
major individual projects that made up
the program and the organizations pri-
marily responsible for the effort.
This Project Summary was devel-
oped by EPA's Air and Energy Engineer-
ing Research Laboratory, Research Tri-
angle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
This volume describes efforts associ-
ated with gas-phase chemistry (GPC)
and provides a detailed account of the
FCR gas-phase effort which was divided
into these principal tasks:
1. Elementary Kinetic Development.
To develop an elementary gas-
phase kinetic mechanism which
describes combustion reactions
for hydrocarbons—through C2
structures—and the fate of fuel ni-
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Table 1. Fundamental Combustion Research Program
Project
Organization
Gas-Phase Chemistry
Kinetic Mechanism Development
The Modeling of Fuel Nitrogen Chemistry
in Combustion: The Influence of Hydro-
carbon
The Formation and Destruction of Nitroge-
neous Species During Hydrocarbon/Air
Combustion
High Temperature Reactor Studies
Physics and Chemistry of Two-Phase Systems
The Physical and Chemical Effects Occur-
ring During the Thermal Decomposition
of Coal Particles
Detailed Measurements of Long Pulverized
Coal Flames for the Characterization of
Pollutant Formation
An Experimental Approach to the Study of
Heavy Fuel Oil Spray Combustion in
Shear Layers
The Characterization of Coals During Ther-
mal Decomposition
Volatility of Fuel Nitrogen
Pollutant Formation from Combusting Pul-
verized Coal Clouds
Pollutant Formation During the Combustion
of Residual Fuel Oils in Backmixed Reac-
tors
Mechanisms of Nitric Oxide Reduction on
Solid Particles
Energy and Environmental Research
Massachusetts Institute of Technology
Exxon Research and Development
Energy and Environmental Research
Energy and Environmental Research
International Flame Research Foundation
United Technologies Research Center
United Technologies Research Center
Rockwell International
Acurex
Battelle Memorial Laboratory
Institut Francais du Petrole
Transport Phenomenon and Engineering Analysis
Development of a Coherent Flame Model
for Turbulent Chemically-Reacting Flames
A Computer Program for General Flame
Analysis
Mathematical Modeling of Microscale Com-
bustion of a Coal Particle
Measurements Support
Chemiluminescent Measurements of Nitric
Oxide in Combustion Products
Measurements of Fuel Nitrogen Species in
Flames
Spray Characterization
The Application of Droplet-sizing Interfer-
ometry and Holography to the Measure-
ment of Spray Droplet Size
California Institute of Technology/TRW
Energy and Environmental Research
Energy and Environmental Research
Energy and Environmental Research
University of Utah
Energy and Environmental Research
Spectron Development Laboratory
trogen (including HCN, NHa, NO,
and the respective intermediates).
2. Data Generation. To generate a
sufficient data base for model veri-
fication for the full mechanism (hy-
drocarbons + full nitrogen). A suit-
able quantity of data for
development of the more complex
portions of the gas-phase model
do not exist.
3. Higher Hydrocarbons. To develop
a methodology for modeling the
combustion of complex hydrocar-
bon fuels. Such modeling is not
currently possible using elemen-
tary reactions.
The GPC effort fell into three principal
subdivisions. Elementary GPC con-
sisted of the compilation and testing of
a comprehensive elementary gas-phase
mechanism which describes fuel nitro-
gen chemistry in hydrocarbon flames.
The maximum complexity of the mech-
anism was limited by the availability of
elementary rate data (specifically, no
hydrocarbons larger than C2 were con-
sidered). The gas-phase mechanism
was tested by comparing mechanistic
predictions against well-characterized
data. For the most complex simulations
(i.e., utilizing the full hydrocarbon/nitro-
gen mechanism) an insufficient number
of data exist for adequate testing. Thus,
a second thrust of the GPC effort was to
generate the necessary data. These
measurements consisted of species
measurements from a jet-stirred com-
bustor and a plug-flow burner.
Assuming an accurate and complete
gas-phase mechanism is assembled,
only hydrocarbon fuels of C2 or simpler
structure can be simulated. The likeli-
hood that the elementary mechanistic
approach can be extended to more
complex hydrocarbons is remote.
Hence, a third thrust of GPC was to de-
velop a quasi-global method of incorpo-
rating some aspects of higher hydrocar-
bon chemistry into the model.
Elementary Gas-Phase
Chemistry
Work on the elementary gas-phase
mechanism proceeded in three well-
characterized divisions: methodology
development, collection of reactions
and rates, and testing and modification
of the mechanism.
The mechanism development
methodology is a system of rules and
procedures governing the testing of
mechanism components and the com-
bination of the components into more
complex mechanisms. The objective of
the methodology is to provide an efff-
cient way to assemble and test the
mechanism while ensuring internal
consistency within the mechanism. Im-
portant features include: (1) careful se-
lection of data for simulation such that
critical questions are resolved (e.g.,
shock-tube ignition delays are used to
resolve questions on chain initiation
and branching portions of a mecha-
nism), and (2) previously proven por-
tions of a mechanism may be modified
only after repeating the original proving
simulations.
The assembled elementary reactions
can be conveniently divided into the
subsets H2/02, CO/H2/02, CH20, NH3,
and HCN, as shown in Figure 1. An ex-
tensive series of tests of the proposed
mechanism were conducted comparing
predictions against various types of
shock-tube and flame data.
The results indicated that the H2/02
and CO/H2/O2 subsets yielded excellent
-------
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Figure 1. Overview of kinetic mechanisms.
agreement with the verification data in
all cases. The comparisons included
shock-tube ignition delays and radical
growth rates, flat-flame profiles, and
flat-flame speeds. General features of
methane oxidation were well repro-
duced; however, radical profiles and
the appearance of C2 species were not
predicted as well. The nitrogen chem-
istry generally predicted the overall re-
duction of fixed nitrogen into N2 quite
well, but was less successful in predict-
ing the reduced nitrogen speciation. In
general, the success of the predictions
corresponded to the number and qual-
ity of the fundamental data used to
derive the rates. Thus, the least studied
systems showed the least successful re-
productions: HCN chemistry, and hy-
drocarbon/nitrogen interaction.
Data Generation
An abundant quantity of data suitable
for mechanism verification for simple
compounds is in the literature. The
usable quantity of data decreases as the
compounds involved become more
complex. Only a very small amount of
literature data is available for testing the
entire (hydrocarbons + fuel nitrogen)
mechanism. Thus, one of the tasks of
the elementary gas-phase chemistry
program was to generate such a body of
useful data.
The approach was to obtain data on
the fate of doped nitrogen in well char-
acterized hydrocarbon combustion en-
vironments. Two experiments were
used: the Exxon jet-stirred reactor and
the Exxon Multiburner (a flat-flame fir-
ing into an isothermal plug-flow reac-
tor). Temperatures ranged from 1800 to
2000 K and equivalence ratios were
varied from 0.7 to 1.8. Fuels were
methane, ethylene, or propane, and
fuel-nitrogen was represented by am-
monia or an ammonia/nitric oxide mix-
ture. The measurements included the
standard combustion products (O2, CO,
CO2, H2, and total hydrdcarbons) and ni-
trogen specification (HCN, NH3, NO, and
N02).
Modeling of Nitrogen
Conversion in Higher
Hydrocarbon Environments
Modeling of combustion processes
by elementary reactions is, of necessity,
limited to hydrocarbons of C2 or simpler
structure. Modeling of the combustion
of higher hydrocarbons has in the past
usually been performed by assuming
some kind of global oxidative pyrolysis
step. Among the possibilities discussed
are:
1. Global oxidation of the hydrocar-
bon fuel to CO2 and H2O following
an empirically determined rate
constant.
2. Two semi-global steps: in the first,
the parent hydrocarbon is oxidized
to CO and H20; and the second
consists of the oxidation of the CO
to C02.
3. Quasi-global methods combine
global steps with elementary kinet-
ics. The usual form has the hydro-
carbon oxidized to CO and H2 by a
global step. The CO and H2 are
subsequently oxidized by an ele-
mentary kinetic mechanism.
The novel quasi-global approach pro-
posed in this study follows the general
form:
Parent Hydrocarbon
Global
Distribution of Hydrocarbon Fragments
Detailed Kinetics
H20
The justification of this technique is
that the oxidative pyrolysis of most
complex hydrocarbons into an array of
fragments of C2 or simpler structure is a
rapid process compared to subsequent
reactions (in particular, fuel-nitrogen
chemistry). The principal accomplish-
ments in this task are:
1. Demonstration of the feasibility of
the approach outlined above. A
study of the literature covering the
pyrolysis into hydrocarbon frag-
ments justifies the assumptions of
the quasi-global mode.
Some of the data needed to assign
speciation to the hydrocarbon
fragments have been obtained.
2.
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W. Seeker, M. Heap, T. Tyson, J. Kramlich, and T. Corley are with Energy and
Environmental Research Corp., Irvine, CA 92718-2798.
Jon E. Haebig is the EPA Project Officer (see below).
The complete report, entitled "Fundamental Combustion Research Applied to
Pollution Formation: Volume I. FCR Program Overview and Gas-phase
Chemistry,"(Order No. PB 86-122 660/AS; Cost: $28.95, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
J
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
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