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U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Summary Report

the Workshop

High Temperai

Chemical Kinel

Application:

Combustion Resec
NATIONAL BUREAU OF STANDARDS

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Bureau of Standfi* 1379 Nummary Report on the Workshop on High

Temperature Chemical Kinetics:

Applications to Combustion Research

[j D. Garvin, R. L. Brown, R. F. Hampson, M. J. Kurylo, and W. Tsang

National Measurement Laboratory

National Bureau of Standards Washington, D.C. 20234

Sponsored by Department of Energy

Washington, D.C. 20545 and

Office of Standard Reference Data

National Bureau of Standards Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director Issued December 1978
Identification of commercial products does

not imply recommendation or endorsement by

the National Bureau of Standards nor that the product is necessarily the best available for the purpose.

Library of Congress Catalog Card Number 78-600125

National Bureau of Standards Special Publication 531

Nat. Bur. Stand. (U.S.), Spec. Publ. 531,89 pages(Dec. 1978) CODEN: XNBSAV

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For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

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Table of Contents

Abstract 1 1. Introduction 1 2. Program of the Meeting 4 3. Commentary on the Meeting

and Suggestions 6 4. Abstracts of Invited Papers 13

5. Discussion of Needs in High

Temperature Kinetics Research 28 5.1 Outline for the Discussion 28 5.2 Summary of the Discussion 31

6. Discussion of Acquisition of High

Temperature Kinetic Data 37 6.1 Outline for the Discussion 37 6.2 Summary of the Discussion 42

7. Contributions Submitted by Participants 49

8. List of Registrants 80

iii

Summary Report on the Workshop on High Temperature Chemical

Kinetics: Applications to Combustion Research

D. Garvin, R.L. Brown, R.F. Hampson, M.J. Kurylo, and

W. Tsang Abstract

The proceedings at a workshop on the applications of high temperature chemical kinetics to combustion research

are summarized. This workshop, held Dec. 12-13, 1977 at the National Bureau of Standards, provided a forum for the exchange of views on the needs for kinetics research during

the next five to ten years. Experimental techniques,

measurements, theoretical developments and data evaluation

were treated in four review papers and two discussion

sessions.

This report contains the program of the meeting, abstracts of the review papers, a commentary by the organizers of the meeting, summaries of the discussions,

formal comments submitted by the participants and an attendance list. Keywords: chemical kinetics, combustion, high temperature

chemistry, reaction rate constants, measurement

techniaues, assessment of needs.

1 . Introduction

On December 12 and 13, 1977, a workshop was held at the National Bureau of Standards, Gaither sburg , MD on "High

Temperature Chemical Kinetics: Applications to Combustion

Research". This workshop was sponsored by the Division of Basic Energy Sciences, Department of Energy and the Office

of Standard Reference Data, NBS. It was attended by one hundred persons, mainly chemical kineticists interested in combustion, but also including researchers concerned with

the modeling of practical combustion systems and the development of diagnostic techniques for probing such systems

.

The objective of the workshop was to provide a forum

for an exchange of views on the needs for high temperature

chemical kinetics research during the next five to ten years, research that would support the development of improved chemical theoretical developments, experimental measurements and data evaluation.

1
Speakers and discussion leaders were instructed to attempt to answer the following questions for each .topic

d iscussed

Why it is important in combustion research? What is the current state of our knowledge? What do we need to know, and how accurately?

What speculative areas should be explored?

What do you see as the research priorities?

Four invited review papers provided orientation for the participants. These papers covered topics in modeling of combustion, the application of laser diagnostic techniques,

combustion chemistry and mechanisms, and the availability

of high temperature rate data. Two extensive discussion

periods were directed toward needs for high temperature

kinetics research and the acquisition of high temperature

kinetics data. This report contains the program of the meeting, abstracts of the invited papers, summaries of the general

discussions, written contributions submitted by the participants and a commentary by the organizers of the meeting. An attendance list is appended.

The association of chemical kinetics and combustion is not new. Almost from the start the programs of the International Symposia on Combustion, organized by the Combustion Institute, have featured kinetic studies of individual reactions and of oxidation systems. The journal

"Combustion and Flame" regularly features articles on kinetics

.

Nor are discussions on the interrelationship of kinetics and combustion research novel, although they have grown in importance recently. In 1974 the National Science

Foundation sponsored a "Workshop on Energy-related Basic Combustion Studies" (Glassman and Sirirnano, 1974) that included an analysis of combustion related kinetics. Problems discussed then are still with us today. In September 1977, Project Squid held a "Workshop on: Alternate Hydrocarbon Fuels for Engines: Combustion and Chemical Kinetics" at Columbia, Maryland. It was sponsored

jointly by the Department of Energy and the Department of Defense. The kinetics topics covered at that meeting and

at the present one overlap extensively. The workshop

reported on here has been followed by a "Workshop on Modeling of Combustion in Practical Systems", held at Los Angeles in January 1978, also sponsored by the Department

of Energy.

2
These interdisciplinary meetings indicate a high level

of concern for the solution of combustion problems on the part of the sponsors. They have enhanced the knowledge of

the participants by exposing them to the problems and needs

of workers in disciplines other than their own. Problems

requiring early solution become apparent. Continued cross- discipline communication should improve our understanding

of the complex phenomenon of chemical combustion.

3
2. Program of the Meeting

Monday , December 12 , 1977 9:15 Welcome and Introductory Remarks

E. Horowitz, Deputy Director

Institute for Materials Research, NBS

J. S. Kane, Director Division of Basic Energy Sciences, DOE 9:30 INVITED PAPERS Session Chairman: L. H. Gevantman, NBS Recent developments in computer modelling of chemical combustion systems.

J. S. Chang and C. K. Westbrook,

Lawrence Livermore Laboratory

10:30 Coffee break

11:00 Advances in laser diagnostics for combustion

research

.

D. L. Hartley, Sandia Livermore Laboratory

12:00-12:45 DISCUSSION: Needs for High Temperature

and Kinetics Research 2:00-5:15 Discussion Leaders: I. Glassman and F . L. Dryer

Princeton University

Reporters: R. F. Hampson and R. L. Brown, National Bureau of Standards
Tuesday, December 13, 1977

9:15 INVITED PAPERS Session Chairman: 0. W. Adams, DOE Combustion Chemistry and Mechanisms.

D. M. Golden, Stanford Research Institute

10:15 High Temperature Chemical Kinetics Data.

D. Garvin and W. Tsang,

National Bureau of Standards

11:15 Coffee Break 11:45-12:45 DISCUSSION: Acquisition of High Temperature

and Kinetic Data 1:45-4:45 Discussion Leaders: S. W. Benson, University of Southern California

D. Gutman,

Illinois Institute of Technology

Reporters: W. Tsang and M. J. Kurylo,

National Bureau of Standards

4:45 Adjournment

Organizing Committee: 0. W. Adams (DOE);

D. Garvin, L. H. Gevantman, R. F. Hampson,

and W. Tsang (NBS) .

5
3. Commentary on the Meeting and Suggestions

W. Tsang and D. Garvin

This section is concerned with the role of chemical

kinetics in combustion research. Topics considered are the types of contribution that kinetics can make , interactions between technological disciplines involved in the study of practical combustion systems , identification of some general problems and a summary of the state of the art. The statements made here are the personal opinions of

the authors. They are not a summary of agreed-upon

conclusions reached at the workshop. No such summary was

attempted, the belief being that information transfer among

the participants should be a primary goal at this stage. But the statements have been stimulated by and draw heavily

on ideas expressed at the workshop. They also incorporate

material presented elsewhere. Other persons undoubtedly

will wish to supplement, revise and refocus these remarks. Combustion research and development involves much more

than combustion chemistry, which, in turn, is a broader

topic than combustion kinetics . The conceptual

organization of the field of combustion has been analyzed

by Essenhigh (ref . 1). His summary is shown in Figure 1. Although this was developed for industrial furnace technology, the translation to other combustion systems is simple. Closely analogous analyses undoubtedly hold for other practical systems that include kinetics, e.g., industrial chemical processing and air oollution control. Three successive stages of activity are shown in Figure

1: basic sciences, technological interactions of basic

sciences, and engineering systems application and development. Studies of reaction kinetics and mechanisms

fall in the basic sciences stage and only begin to be applied to combustion at the technological stage, where j they are combined with the outputs from other sciences. Direct interaction of kinetics with the engineering stage

is not shown. Instead, the scientific results are processed via major new concepts introduced at the other

stages. Inevitably, the details considered important at the basic sciences level are hidden (or lost) in the final outputs.

6
This leads to an appearance of strong decoupling of the sciences from the final outputs and makes it very difficult

to attribute improvements at the engineering level to advances in the sciences. That this decoupling is not real

is becoming apparent as detailed modeling is applied to practical combustion systems. Two conclusions from a recent modeling study bear on this point. Griffin et al

.

(ref. 2) modeled the fluid dynamics of the internal combustion engine. Their model included a detailed kinetic description of the chemistry. They stated:

"The combustion process in the IC engine can be represented by finite-rate chemical reactions.

The solutions are subject to inaccuracies in the rate data." They also concluded:

"A partial mechanism can simulate the heat process due to combustion, but the complete

mechanism is required to compute the pollutants

accurately. n The first quotation provides evidence of a direct influence

of the scientific research on the final output. That influence would be there, although perhaps diluted and certainly hidden, in design studies that did not use explicit modeling techniques. The second speaks to an ever-present problem: simplified chemistry can be used for studies of limited scope, but different chemistry is important in different problems.

Within the discipline of chemical kinetics there is a widely held belief that detailed study of the chemistry

that occurs in oxidation and pyrolysis systems (mechanisms)

and quantitative data on the important elementary steps

(rate constants) will be required for a satisfactory

specification of combustion. That belief is valid and is supported by experience with partial solutions. It helps

explain why the study of combustion kinetics is a goal in itself, independent of the consideration of practical

systems. Indeed, oxidation kinetics are sufficiently

complex to require the full attention of the specialists in the art. The same is true for other scientific disciplines

pertinent to combustion. Thus there is a self-imposed

disciplinary decoupling, in the interest of solving the "local" problems, that may be a major barrier to ,the development of coherent combustion research programs.

7
Although a detailed understanding of kinetics may be necessary for the advancement of combustion research (it certainly is not sufficient) , it is not apparent that this generalized approach can be pursued rapidly enough for the results to be widely useful in technological studies. The problem is that there are many practical combustion systems

and the study of them is going on in parallel with the work

on kinetics. This indicates a need for establishment of priorities for kinetics studies and a need for more interdisciplinary interactions than in the past.

Nobody has solved the problem of establishment of priorities within a research community that consists of many independent small research groups, and we do not attempt to do so here. Clearly any priorities must be related to the applied problems that will be important in the near future (research takes time, impact on immediate problems is likely to be small) . But priorities for scientific studies that are stated in terms of the performance of engine X or furnace Y are inappropriate and are, themselves, decoupled from the sciences. More useful priorities would cover classes of behavior applicable to several combustion systems. They could be stated in terms

of needs for basic studies that would aid in the solution

of identified technological problems, e.g., quench-layer

kinetics in internal combustion engines, soot formation,

pyrolysis in fuel droplets, pollutant formation in the oxidation of alternative fuels or ignition in aromatic

hydrocarbon-air mixtures. It is then up to the kineticists

to translate these needs into possible experiments, and explain what parts of the problem can be solved. The situation is more promising with respect to interdisciplinary interaction. Most important is the direct feedback from modeling studies. Because models use detailed kinetics, and because sensitivity analyses of them

can point out areas of weakness, they can indicate research

needs. In addition, the explicit display of the chemistry

used in the models permits the kineticist to determine

whether or not that chemistry is consistent wih fundamental

studies. We suggest that such analyses should be given the status of a branch of combustion kinetics. Interpretation and simplification of kinetics for the benefit of others is another promising area of interdisciplinary work. The combustion scientist may properly ask: "which aspects of the chemistry are important in my problem and which can be ignored for the present?" The person studying spray combustion, however

8
expert in his own field, should not be expected to be knowledgeable about reaction mechanisms or estimating rate constants. Guidance from the kineticist is desirable. One

form of this is the development of simplified ("global")

mechanisms. But extensive collaboration probably is required, as opposed to general guidance. We suggest that

such collaborations should be promoted.

The discussion above covers general aspects of the role

of kinetics in combustion. We conclude this section by

listing some specific conclusions. Most of these are concerned with the state of the art within the discipline

of combustion kinetics, but some touch on the general

topics considered above.

1. Chemical kinetics of high temperature transformations

involving hydrocarbons and related compounds are essential for the conceptualization, understanding,

control and optimization of combustion devices.

2. Types of needed information range from general mechanisms

to detailed single step rate constants. They cover heterogeneous as well as homogeneous phenomena and involve the oxidation and pyrolysis of aliphatic,

aromatic and heterocyclic compounds. Data on pollutant

formation is particularly important. These reactions

cannot be decoupled from the basic combustion process.

3. Global rates constants are needed for the modeling of specific devices. They are not transferable and can be entirely empirical but preferably should be traceable

to the pertinent set of single step rate constants.

4. Traditional engineering usage has place greater reliance

on general mechanisms as opposed to the detailed

kinetics necessary for computer simulations. The latter represents a growing research area and has enormous potentials for providing complete and general

solutions and, ultimately, as an alternative to physical testing.

5. There is a serious lack of mechanistic information on

the pyrolysis and oxidation of aromatic and heterocyclic systems. Thus the information for the design of combustion devices using various coal derived

fuels even on a traditional basis does not exist.

6. Although the mechanisms of the oxidation and pyrolysis

of aliphatic hydrocarbons are fairly well understood,

large numbers of the needed rate constants remain undetermined. There is a particular need for data on hydrocarbons larger than methane.
7 There exists a vast arsenal of kinetic tools for the determination of the mechanism and rates of high

temperature transformation in the gas phase. • All reactions involving ground state molecules probably are accessible. There has been however no systematic

effort (similar to that for stratospheric pollution) in this direction.

8. Transition state theory provides a possible framework

for the extrapolation, prediction and correlation of rate parameters. Critical tests are still necessary. Particular information needs include thermal properties

of unstable species as well as rate determinations.

9. In all kinetic studies proper understanding of mechanisms

must precede accurate rate determinations. Particularly

important is the application of a variety of experimental

methodologies to the same system. Laser based techniques have qreat potential but there are severe limitations especially in complex systems with multiplicity of species (as in combustion) . More traditional techniaues, with capabilities for total analysis, e.g. gas chromatography and mass spectrometry will continue to play key roles with

respect to unraveling mechanisms.

10. Computer modeling of combustion or other reactive systems

is still in its infancy. There appears to be a direct

need for the establishing of proper methodology in the development and extraction of information from models. Algorithms for carrying out sensitivity analysis and application to combustion systems must be developed.

11. There is essentially no capability in the combustion

kinetics community for supplying detailed single step

quantitative data on condensed media or multiphase

reaction processes. These are research frontier areas

and careful studies on model systems, with extensive

aid from computer simulations will be of more lasting value than direct studies in combustion environments.

At present the best that can be expected from such work

is qualitative mechanistic information. Soot formation

and reactions in or on soot also falls into this category. Homogeneous gas phase reactions are in general important components of these processes.

Proper understanding of these processes may be a prereauisite for advances.

12. It is likely that there are too many physical properties

of interest for combustion studies (rates,

thermodynamic data) for all to be measured. The appropriate tactics are: (a) measure the most * important, and (b) estimate the remainder.

10
References

1. Essenhigh, Robert H. , "Research Opportunities for Universities in Combustion of Coal", Proceedings of Conference on "Research Opportunities for Universities

on Coal" OCR/NSF-RANN, SUNY, Buffalo, NY, October,

1974 . 2. Griffin, M. D. , Diwaker, R. , Anderson, J. D. , and Jones, F. , "Computational Fluid Dynamics Applied to Flows in an Internal Combustion Engine", AIAA 16th Aerospace Sciences Meeting, 78-57. Huntsville,

Alabama, January 16-18, 1978.

1

ii
12
4. Abstracts of Invited Papers COMPUTER MODELING OF COMBUSTION CHEMICAL KINETICS

J. S. Chang and C. K. Westbrook

Lawrence Livermore Laboratory

P.O. Box 808, Livermore, California 94550 ABSTRACT

Computer modeling of chemical kinetics in combustion

systems is a complex chemical, physical, and mathematical

problem. In most practical applications, chemical

reactions are closely coupled to other physical processes,

adding further difficulties to the analysis of the chemical

kinetics features of the combustion. In this paper we will

try to indicate the degree of sophistication which is currently possible in numerical models of detailed chemical

reaction mechanisms. We will also describe some of the methods used for simplifying or idealizing real combustion

systems in order to make their analysis possible, using

available numerical methods and computers. Finally, we describe what we feel are the most probable directions in which kinetic modeling for combustion applications is likely to proceed.

In addition to chemical kinetics, most combustion

systems involve a variety of other physical processes,

including mass and energy transport by means of either molecular diffusion or turbulent transfer. In some systems

multiphase flows occur, with liquid atomization and vaporization processes in many of these situations.

Radiative heat transfer may be important, and surface

effects, including wall heat losses and catalytic

combustion, may occur. In each large class of real combustion systems a somewhat different and distinct set of physical operators contribute to the overall system

performance. Many, if not all of these physical

operators are themselves extremely difficult to model computationally. In view of this degree of complexity, it is desirable to place our initial emphasis on physical

systems in which chemical kinetics is the dominant physical

operator. Some such systems are one dimensional laminar

flames, shock tubes, and the turbulent flow reactor. These configurations are often either time-independent or spatially invariant, greatly simplifying the computational

13
analysis. We will show results of several computations

made for laminar flame structure and propagation,, as well

as results of turbulent flow reactor experiment modeling

for a variety of fuels.

It is our opinion that for a pure kinetics problem, a mechanism of any reasonable size can be handled numerically

by available methods and computers. This capability would

extend to kinetic mechanisms involving up to several hundred chemical species and many hundreds of chemical

reactions. Since known reaction mechanisms are much

smaller than these sizes, this statement includes any currently proposed reaction mechanisms. The computational

difficulties begin to arise when spatial variations are introduced. While the pure kinetics problem might include

20 equations (species) , a two-dimensional axisymmetr ic combustion chamber with a resolution determined by a 50 x 50 computational grid would require the solution of approximately 50 x 50 x (5 + 20) or 62500 equations for each time step. Since the computational time is required

for a problem of this type depends roughly on n , where

is the number of equations, the two-dimensional problem

quickly becomes intractable. Inclusion of detailed

reaction mechanisms for problems with one space dimension

can be rather expensive but is possible, and some examples

will be shown of stratified charge internal combustion

engine studies in one space variable.

Since two- and three-dimensional geometry precludes the inclusion of detailed reaction mechanisms, it is necessary

to find alternative kinetic models for these problems. We will briefly discuss a number of global, quasi-global, and semi-global reaction mechanisms in present use, some of their properties, and some examples of their use in turbulent flow reactor simulations. Several other schemes

will also be discussed, including species "lumping 58 , partial equilibrium assumptions, and partial decoupling of portions of the kinetic mechanism for species purposes,, We will discuss a number of combustion areas in which

chemical kinetics are either dominant or present special

problems, either in practice or with respect to their modeling. These include NOx , SOx , and soot formation,

ignition processes, and catalytic combustors. In addition,

we will describe a series of numerical studies of reaction

quenching by a variety of physical mechanisms. These

include quenching by a thermal boundary layer (wall

quench) , by a sharp gradient in equivalence ratio (volume

quenching) , and by a rapid expansion of the combustion

chamber (bulk quenching)

.

14
We have attempted to indicate areas in which combustion

modeling has specific needs for which kineticists may help

provide solutions. Most obviously, there are a multitude

of elementary chemical reactions for which rate data are unavailable or unreliable. Thermochemical data and reaction mechanisms are also needed for most practical

combustion fuels. In many fuel oxidation mechanisms,

kineticists could provide insight into identifying the important and rate-controlling steps. This would help in two major ways. First, it would help to validate the detailed mechanisms used in thermodynamic (0-D) and one-dimensional models. Also, it would motivate the selection of semi-global or overall steps which could be used to simplify reaction mechanisms for use in larger models. Another important function would be to indicate

the degree of detail necessary , including species,

elementary reactions, and reaction rates, for different

appl ications

We will briefly discuss coordination between modeling

and diagnostics. It is important for the modeler to recognize the limitations and possibilities of experiments,

including concentration, temperature, and velocity

measurements. Problems exist for both types of research

with respect to physical resolution, accuracy, and other properties. We see a definite value in designing idealized

experiments to emphasize kinetic effects in much the same manner as noted earlier for modeling purposes. And model validation by comparison with a variety of well documented experiments is very important. We also recommend that, as part of its data base development, NBS provide critical

evaluation of selected experiments which emphasize kinetic

effects. These experiments can then be very useful as model validation vehicles.

We find that reaction rate data is best represented by

Arrhenius coefficients. However, temperature regimes in combustion environments can vary from room temperature to over 3000 K. Many important reactions display significant

non-Ar rhenius behavior over this range, and it would be helpful for a data base to find a convenient way to handle

this behavior within a basically Arrhenius framework. We also believe it would be very useful to maintain data for heats of formation, equilibrium coefficients of formation

in both tabular and Arrhenius form, reverse reaction rates,

and all manner of thermochemical data. While we realize

some of this information is redundant and perhaps even formally inconsistent, it would greatly assist many modeling programs.

15
ADVANCES IN LASER DIAGNOSTICS FOR COMBUSTION RESEARCH

D. L. Hartley

Combustion Sciences Department 8350 Sandia Laboratories

Livermore, CA 94550 ABSTRACT

Numerous advances have been realized in recent years in developing and applying new measurement techniques for experimental studies of combustion processes. Intrusive

probes such as thermocouples and sampling probes have provided a wealth of information on combustion systems and undoubtedly will continue to do so. More recently,

however, with the advent of electro-optic devices such as lasers and the rapidly developing array of detectors,

techniques for measuring properties in combustion systems

are being developed which do not require physically probing

the experiment with a perturbing probe, but rather use some form of optical scattering to measure flow conditions.

The importance of these optical scattering techniques

arises from their ability to provide excellent time response from essentially a point measurement in space as well as to overcome the limitations of physical probes. These limitations are largely related to the disturbance

that they impose upon the system under study, the difficulty in surviving the hostile environment presented

by combustion systems, and the difficulty in many cases of relating the measurement to properties of interest. Optical scattering techniques can be used to overcome many

of these limitations for a large number of research problems

.

During the last few years, several studies have been conducted by various segments of the scientific community

to assess the status of optical scattering methods and to identify their limitations and the potential for extending

their capabilities to problems in combustion research. In 1974, the American Physical Society conducted a summer study on the role of physics in combustion and highlighted

optical diagnostics (Ref. 1). In 1975, Project SQUID conducted a workshop focused on combustion diagnostics in jet propulsion systems (Ref. 2). In 1976, the AIAA emphasized combustion diagnostics in their annual National

16
meeting and published special proceedings containing most

of these papers (Ref . 3) . In 1977 the EPA sponsored a study at United Technologies to provide a detailed review

of laser techniques for practical combustion diagnostics

(Ref. 4) and ERDA sponsored a study at Sandia addressing

the application of these techniques to measurements in coal-fired gas turbines (Ref. 5)

To underscore the importance of optical diagnostics in combustion research, the DOE has approved the construction

of a Combustion Diagnostics Facility at Sandia in Livermore, California, where several specially designed

diagnostic systems will be made available for qualified

users. This facility will be operational in mid-1980.

The purpose of this presentation is therefore twofold.

On the one hand, this paper will introduce these techniques

and their current status to the chemical kineticists in the audience who may be interested in potentially using them in their own research. On the other hand, feedback from this workshop will help formulate decisions concerning

diagnostic equipment choices at the Combustion Diagnostics

Facil ity

Hopefully reflecting the special interests of researchers in high temperature chemical kinetics, I will limit the discussion of diagnostics to those which are capable of measuring species concentration and temperature

over regimes of their interest. The techniques I will discuss are elastic Rayleigh scattering; linear inelastic

scattering such as spontaneous Raman; resonant Paman and fluorescence; line-of-sight absorption; and several nonlinear optical processes including Coherent Anti-Stokes

Raman Spectroscopy (CARS) , Stimulated Anti-Stokes Raman Spectroscopy (SARS) , Raman Induced Kerr Effect Spectroscopy

(RIKES) , and High Order Raman Spectral Excitation

Spectroscopy (HORSES)

A brief description of field image techniques; laser

shear inter ferometry and Ramanogr aphy , will also be presented

In this abstract I shall discuss only a few principal

scattering techniques, namely Rayleigh, Spontaneous Raman, Fluorescence and some of the nonlinear optical techniques.

Rayleigh Scattering is an elastic scattering of photons

by the irradiated molecules. Being elastic, the scattered

light experiences no characteristic shift in frequency,

17
thus it can only be used to measure total number density

or, by resolving the Doppler line width, may be used to measure temperature. Although of limited versatility,

Payleigh scattering has been used recently to measure temperature profiles in diffusion flames and to measure density profiles through a moving flame front. The high

scattering cross-section makes Rayleigh scattering easily

applied by laboratory researchers.

Raman Scattering is an inelastic process in which the scattered light has undergone a change in frequency

characteristic of the internal energy levels of the irradiated molecule. For the applications discussed here, these internal modes are the vibrational and rotational energy level manifold. The intensity of light scattered at

a given Raman wavelength shift (small shifts for rotational, larger shifts for vibrational) can be related directly to the number density of molecules of that particular species in the sample volume. For high

-temperature gases, high molecular energy levels are populated increasingly, and the resulting distribution of intensity among Raman scattering lines is altered accordingly. Measurement of this redistribution of energy

(i.e., shifts in intensity of ground-state and excitedstate vibrational Raman lines) can be used to determine gas temperatures

.

In compensation for the low signal strength of Raman scattering, its virtues include (1) specificity of species

identity, (2) time resolution not limited by scattering process (10-14 sec) , (3) accessibility of temperature

information, (4) capability of probing systems not in chemical or thermal equilibrium, and (5) relative lack of interferences. Numerous applications of spontaneous Raman scattering

to combustion research have emerged in the last two or three years. Laboratory systems, including flat flames and diffusion flames, and practical systems from internal combustion engines to gas turbines have been probed with Raman systems with varying degrees of success. These results shed considerable light on the potential range of application of spontaneous Raman scattering to problems in chemical kinetics. "Typical" conclusions for Raman scattering studies at a gas turbine inlet (Ref. 5) are that in the absence of limitations due to particulates or laser- induced spectral background (both problems yet to be completely evaluated) , 2 a errors of less than 10% are

18
predicted for total measurement times of 0.02 to 0.5 seconds for all major species (N2, 02, C02, H20 and 0.8 to

80 seconds for minor species (NO, CO, S02) using a conventional cw laser or advanced high- energy pulsed laser

(one joule per pulse, 10 pulses per second). Laser Fluorescence like Paman scattering, can be used

as a species-sensitive optical detection method. Fluorescence techniques, using cw or pulsed tunable laser sources in principle offer the possibility of extremely

sensitive detection of both atomic and molecular species.

However, since fluorescence is an absorption and re-emission process, quenching and pressure broadening make data interpretation difficult. For this reason, fluorescence techniques involving saturation show greater

promise since such approaches minimize the problem of quenching. Typical molecule s of interest, which have an absorption wavelength that is accessible to tunable laser sources (roughly 0.2-1.5 microns) are C2, CH, CN, CS, NH

,

NH2, NO, OH, S02, HCN , CH20, C6H6, and C10H8. Since the fluorescence cross-section s are many orders of magnitude

greater than those for Raman scattering, fluorescence detection of minor species concentration is currently

receiving considerable attention for combustion

d iagnost ics

.

CAPS is a nonlinear optics process that recently has been shown to be of great promise as a combustion probe. CARS is a three-wave mixing process., requiring two light sources, one of adjustable frequency. For the purpose of explanation, one beam will be referred to as the pump beam

at frequency w and the other as Stokes beam wa

. These two beams are focused colinearly into the sample volume. When

the frequency difference between the two beams is equal to

a Raman shift for a gas in the sample volume, a coherent anti-Stokes Raman beam of frequency w ff

' is produced by the interaction with that gas. The scattered beam is almost parallel to the incident

beam and is many orders of magnitude more intense than spontaneous Raman scattering. The CARS signal, however, is no longer a simple linear dependence on laser power and number density, as is spontaneous Raman scattering.

Instead, the signal is proportional to Stokes laser power,

the square of the pump laser power, and the square of the density. This nonlinearity in functional dependence on

input conditions places potential limitations on the application of CARS to many practical combustion

environments. The work by Taran and his coworkers has

19
addressed many of these limitations and capabilities of CARS and has been the pioneering effort to make CARS a practical system for combustion research. CARS appears to be very good for thermometry and for major species

detection (>1000 ppm) . For minor species, however, the probability of success is much poorer.

SARS and RIKES are other nonlinear techniques which

offer relief from the intrinsic background problems of CARS. Also in contrast to CARS, these techniques do not require phase matching and the spectral output is similar

to spontaneous Raman scattering and thus relatively easy to interpret. However, for both of these systems the detection apparatus can be very complex. These techniques

are still in their infancy and need considerable

development before their potential can be better understood

.

For each of the techniques mentioned above, limitations

exist which are yet to be completely resolved. Nonetheless, over the last few years, their range of applicability has been demonstrated over an increasing

number of problems, and these gains are illuminated in the recent reviews referenced herein. In general, these systems are expensive ($50K to 200K) and require a trained

user. The techniques are not yet developed to the point of casual application and this may never be the case. However, for the interested researcher in chemical

kinetics, the problems (and risks) of setting up one of these techniques for his use are significantly lower than a few years ago. Today a number of integrated systems are in use which can be used as models and the number of knowledgeable users is greatly increased.

The Combustion Diagnostics Facility at Sandia is being

organized and equipped to provide training on these optical

techniques, to improve and simplify integrated diagnostic

systems, and to make various techniques and state-of-the-art equipment available to users from the combustion research community.

2 0
REFERENCES

1. Hartley, D. L. , Hardesty, D. R. , Lapp, M. , Dooher , J., and Dryer, F., "The Role of Physics in Combustion,"

Efficient Use of Energy , AIP Conference Proceedings , No. 25, 1975, New York.

2. Goulard, R. (ed.), Combustion Measurements , Modern Techniques and Instrumentation , a Project Squid

Workshop, Academic Press, 1976.

3. Zinn, B. (ed.), Experimental Diagnostics in Gas Phase Combustion , Progress in Astronautics and Aeronautics, Vol. 53, New York, 1977.

4. Eckbreth, A. C. , Bonczyk, P. A., and Verdieck, J. R.

,

Review of Laser Raman and Fluorescence Techniques

for Practical Combustion Diagnostics , United

Technologies Research Center Report UTRC-R77

,

952665-5, 1977.

5. Coleman, H. W. , Hardesty, D. R., Cattolica, R. J., Pohl , J. H., Rahn, L. A., Hill, R. A., and Hartley, D. L., Interim Report: Diagnostics Assessment for Advanced Power Systems , Sandia

Report SAND77-8216, 1977.

21
COMBUSTION CHEMISTRY AND MECHANISMS

David M. Golden

SRI International

333 Ravenswood Avenue, Menlo Park, CA 94025 ABSTRACT

Understanding of the chemistry involved in combustion

requires the general understanding of mechanisms of pyrolysis and oxidation. The object is to write a mechanism and to evaluate individual rate constants within

some framework. Hopefully, this will eventually facilitate

the generalization of such mechanisms for efficacy in modeling

.

The framework most often employed is that of transition

state theory. In this paper we will explore the validity

and limitations of the use of transition state theory as a framework and suggest some possible experimental probes of the questions raised. Experiments have been performed for many years to determine the temperature (and pressure) dependence of rate constants for elementary chemical reactions that are postulated to be important in pyrolysis and oxidation of hydrocarbons. Even though more sophisticated experimental

techniques continue to become available, it will never be possible to measure all possible reactions under all possible values of temperature and pressure. This impossibility will not present us with insurmountable

difficulties if we have a fundamental understanding of the nature of thermal elementary reactions which allows us to extrapolate data for specific reactions to temperature (and pressure) ranges which have not been measured, as well as to other similar reactions.

A good deal of success in establishing a framework for codification and extrapolation of rate data has been achieved with transition state theory. I will review some of the many examples where transition state theory serves

as an adequate framework for rate data analysis. This will include the prediction of rate constants and their pressure

and temperature dependence. We will see that critical data analysis based on transition state theory considerations

has been helpful in calling our attention to systematic

22
problems with certain experiments. Particular attention

will be paid to entropy and heat capacity of activation as

a criterion for understanding the details of a chemical

reaction.

Thus, for example, we will review the fact that the "A-factors" for atom metathesis reactions, often available

over a modest (~300-800 K) temperature range decrease for a given substrate as the reactive radical becomes progressively larger, reflecting the loss of entropy due to external degrees of freedom. Reaction log [A/M-ls-1]

H + C2H6 ~ 11 OH + C2H6 ~ 9.5 CH3 + C2H6 ~ 8.5 We will also recall that abstraction of an H-atom to form a stabilized species reflects the smaller value of entropy in the transition state.

CH3 + C3H6; log [A/M-ls-1] ~8.0

We will discuss other examples of validity of this approach, which will include some discussion of pressure dependence of rate constants as well. Having established the validity of the thermochemical

kinetics approach, we will explore some limitations.

Limitations include the fact that reported temperature

dependencies for simple H-atom metathesis reactions often

exceed those predicted at temperatures greater than 1000 K. On the other hand, some specific examples have recently

been published of reactions with temperature dependencies

that are less than predicted. Since some of these data are obtained in fairly complex experiments, there exists a strong need for direct measurements of selected reactions

over a long temperature range. Experiments should give data about products as well as rate parameters because often reactions may proceed by multiple pathways. This is particularly possible at higher temperatures. Specific

suggestions as to needed data will be made.

In addition, many simple reactive systems have been

shown to proceed to specific product states. If this is accepted as a general characteristic of elementary

processes, a legitimate question about the validity of a 23
statistical theory, such as transition state theory, is raised. This question will also be discussed.

Finally, I will address the question of general

mechanisms for oxidation and pyrolysis of aliphatic and aromatic hydrocarbons.

24
HIGH TEMPERATURE CHEMICAL KINETICS DATA

David Garvin and Wing Tsang

National Bureau of Standards, Washington, DC 20234 ABSTRACT

A data base of reaction rate constants is needed for use in combustion research. This data base must as a start consist of rate constants for elementary thermal reactions. Data on single step reactions are applicable to all systems

that may be studied whereas global rate constants are useful only in specific systems and are not transferable.

Global rate constants can and should be developed from the elementary rate data base and the applicable mechanisms. State-to-state and molecular beam experiments can give valuable mechanistic information, but, today, cross sections derived from them are not easily usable in combustion problems. In time they can be folded in and guide the study of non-equilibrium aspects of combustion.

There has been a modest decline in the total number of gas kinetics measurements in recent years. But high

temperature measurements (above 500 K) have decreased more

sharply, limiting the growth of the combustion data base. Low temperature measurements have increased in recent years

as pollution and atmospheric chemistry problems have come

to the fore. One important result is that the high

temperature data base is old and items in it only rarely

are based on the modern higher precision experimental

methods. Adaptation of these methods to high temperature

kinetics is needed. Substantial numbers of rate constants gas phase

reactions have been reviewed and recommended rate constants

have been published. Most of the reactions in the H2/02

system have been reviewed. The CH4/02 system is also reasonably well covered. Rate constants for the overall reactions of H , 0, OH, H02 and CH3 with organic molecules have been codified, but

in some cases the data are sparse and only rarely have the branching ratios been considered. Rate constants for the initial steps of pyrolysis reactions are reasonably well

under control although much of the data base is old. The reviews should be updated. In contrast several classes of reactions need extensive evaluation work. Reactions of molecular oxygen have not been evaluated systematically. Processes leading to carbon formation are poorly

25
understood. Radical-radical combination reactions deserve more work and are getting it - both experimentally and theoretically. The outlook is promising. Radical

d ispropor tionation reactions are much less well understood

and have not been systematized. The combustion scientist

faces three problems in using these codified data: they are reported in many sources, they are often based on data

that have large error ranges and, inevitably, exactly the reaction for which data are needed today are missing from

the collections. Programs are needed that will pull

together the scattered recommendations, that will provide

higher precision measurements on key (sensitive) reactions

and that will fill gaps in the data base by the use of estimation techniques.

It is difficult for the kineticist to determine which measurements should have high priority. Several approaches

are desirable. Reactions that delineate combustion

mechanisms should be studied. Even qualitative mechanistic

information is very valuable. Reactions that make possible

the development of correlations for classes of reactions

should be emphasized. Rate constants for reactions to which models are very sensitive should be measured carefully and remeasured if older data have large errors. The usefulness of guidance from modelling studies is indicated above. But modelling of laboratory experiments

on reaction kinetics also should be fostered. Most high

temperature experiments involve many elementary reactions

and require elaborate interpretation of data. This can be made more reliable by modelling. The technique of sensitivity analysis should make it possible to set more realistic error limits for rate constants.

The art of data evaluation needs further development if its output - recommended rate constants - is to be reliable

enough for application to combustion models. Guidance is needed from theory in order to improve judgements on the validity of data. Transition state theory and unimolecular

rate theories have already proven their usefulness in the interpretation of rate constants and should be pushed to develop a framework for the techniques for extrapolation of data to different temperature and pressure regimes. They

also are the starting points for the establishment of correlations among closely related reactions. Gas kineticists also have much to learn from the physical

organic chemists.

26
Empirical and semiempir ical techniques for estimating

rate constants should be the subject of a major effort. They may be the answer to rapid expansion of the present

data bank. The development of estimation techniques has been an active although small part of kinetics for decades. Twenty five methods have been identified. The more promising ones should be studied, validated, and their ranges of applicability determined.

While a kinetics data base for combustion studies will emphasize oxidation and pyrolysis reactions, these classes

are too restrictive for present needs. Combustion kinetics

is high temperature kinetics _in toto . One must be able to handle energy release steps, to treat pollutant formation

and control, to explain the behavior of additives and to meet as yet unseen needs. In addition a wide range of high

temperature measurements - accurate ones - is needed to guide the theoretical developments and correlation work

that will bolster the art of data evaluation.

27
5. Discussion of Needs in High Temperature Kinetics Research Discussion Leaders: F . L. Dryer and I. Glassman

Princeton University, Princeton, NJ 08540

5.1 Outline for the Discussion

Many topics in this area that need to be considered by the kinetics community are listed below. This outline is intended to serve as a guide for the discussion.

A. Aromatics Pyrolysis and Oxidation Kinetics Mechanisms

1. How are these different for benzene, alkylated

benzene and polynuclear aromatics? The same question must be asked about the specific problems

in the following subsections.

2. Initiation and attack on aromatic ring (leading to fragmentation) . Different for premixed and diffusion flames?

3. Chain branching steps - do the H2-02 branching

steps play same role as in reactions of aliphatics.

4. Production of major oxidation products - Carboxyl groups form, how? How do they break away from fragmented ( ?) ring, what are their fate?

5. What nitrogen fragments form and how, particularly

from coal at fluidized bed temperature, what is the fate of these nitrogen fragments, what are the other competitive steps for oxygen atoms?

6. Same as 5, above, for sulfur.

B. Soot and PCAH (polycyclic aromatic hydrocarbon)

Formation

1. What are the elementary processes in the gas-phase,

including nucleation.

2. Does the process change with the character of the flame (pre-mixed or diffusion) for aromatics?

3. What radicals attack soot precursors most readily

and how?

4. Kinetic mechanisms of soot inhibitors and promoters.

28
5. Is surface oxidation of soot and carbon (graphite)

vastly different? Coal char? Does C02 form at all on carbonaceous surfaces? Can it be due to catalytic effects?

6. What are the liquid-phase pyrolysis reactions

leading to cenospheres? How are they affected by

impurities and dissolved oxygen?

C. Overall Rate Expressions

1. Which systems hold promise for these short-cut procedures?

2. What are the limitations of this approach?

D. Sulfur Oxidation Kinetics

1. In particular, what is the mechanism of oxidative

attack on organic sulfur leading to S02?

2. Why is S03 formation in real systems so sensitive

to stoichiometry?

E. Heterogeneous Kinetics

1. Quench layer kinetics - completely obscure or well-known? Is it the region of odor (aldehyde)

formation in diesels? What problems really exist

in sampling probes?

2. Of f-stoichiometr ic catalytic combustion fuel-oxygen

reaction on surfaces - simply a mechanism for supply of radicals to gas phase or a mechanism

for complete conversion to major products?

3. Catalytic surface combustion related to sulfur and nitrogen containing fuels.

F. Aliphatic Oxidation

1. Importance of H02 reactions in aliphatic and CO oxidation

.

2. Rate data for H02 reactions.

3. More work on acetylene and olefin oxidation kinetic mechanism at high temperatures.

4. Oxidation in very rich mixtures - effect of 02 and H20 on pyrolysis.

29
G. NOx Formation and Reduction

1 . Do we already know enough about NO formation

reactions?

2. Should we not concentrate on mechanisms and rates

of NO reduction reactions?

H. Thermal and Oxidation Stability of Alternative Fuels

1, A very important medium temperature range kinetics

problem.

2. Kinetic mechanisms of in-situ combustion recovery

of shale oil and other thermal and chemical

secondary and tertiary recovery schemes*

I. Chemical (Homogeneous and Heterogeneous) Inhibiton of Flame Propagation

1. Lean-limit kinetics (fuel safety problems).

2. Anti-knock kinetics.

3. Effect of large halocarbons molecules on lean-limit

and stoichiometric combustion.

30
5.2 Summary of the Discussion

P.L. Brown and R.F. Hampson

The session on the first day began with the presentation of two invited papers [Chang and Westbrook,

and Hartley] and a survey [Dryer and Glassman] on the needs

in high temperature kinetics research. Aspects of all of these are pertinent to an understanding of the general

discussion and are reviewed here.*

In the first paper Westbrook reviewed the subject of computer modeling of combustion systems. He pointed out that chemical kinetics is but one subsystem of a combustion

system involving a large variety of other closely coupled

physical subsystems. Modeling can be done on three levels

of sophistication - subsystem modeling, parameterized

modeling, and system modeling. Combustion systems are characterized by energy production by chemical reactions

and the most distinctive feature is that chemical kinetics

drives the system dynamics. For some systems such as one- dimensional laminar flames, shock tubes and turbulent flow reactors, chemical kinetics is the dominant physical

operator. He discussed the modeling of results reported by

Dryer and Glassman in the Fourteenth Symposium on Combustion for the oxidation of CO and CH4 using a turbulent flow reactor. (Reference 1) The agreement with experimental data was excellent. He also discussed the modeling of recent results on CH30H oxidation. The conclusion reached from this purely kinetics modeling is that any reasonably sized mechanism (up to 500 reactions

involving 200 species) can be handled with present day

computers and computer techniques. The number of differential equations one must solve depends on the number

of species and not the number of reactions. The computational problem increases dramatically when one attempts to couple the kinetics with fluid mechanics. For example, a 2-dimensional flow problem using a 50 by 50 computational grid, 5 hydrodynamic variables, and 5 chemical species requires 25000 differential equations to be solved at each time step. Statements made during the discussion are attributed to individuals only if they submitted written comments. For those cases, references are given to numbered comments in Section 7.

31
Some kind of kinetic simplification is needed to keep

the computer costs within reasonable bounds. Westbrook

discussed a number of alternatives to the use of detailed

chemical kinetic mechanisms. These include the use of global type mechanisms. Other techniques use "lumping"

methods, radical pool concepts and partial equilibrium

calculations. The principle under-lying these techniques

is the attempt to reduce the number of equations to be solved by replacing a differential equation by an algebraic

equation. Another technique to reduce the number of equations is partial decoupling of the mechanism for trace species. He discussed a number of representative problems where chemical kinetics are crucial to an understanding of the physical system and where the solution to the problem

can be said to be "kinetics information limited". These include NOx and SOx formation, soot formation, catalytic

combustion, spark ignition processes, and quenching. For the application of modeling to practical combustion systems

a large extension of the data base is needed. There are many important fuels, and the only one we have a good

mechanism for is methane. We need detailed chemical kinetic data, reaction mechanisms, and thermo- chemical

data for other fuels. Combustion problems cover an extremely wide temperature range; modelers much prefer

using functional forms for temperature dependence rather

than tabular data. Thermochemical data are often the hardest to obtain. In the general discussion, Westbrook

(7-1) referred to the question of the coupling between kinetics and fluid flow and recommended including transport

properties in a kinetics data base. Following this talk, an opinion was expressed that most chemical kinetics shown in detailed mechanisms is irrelevant, with most systems being sensitive to a very few number of reactions. However, the majority feeling was that although a simplified mechanism can be devised to describe many systems over narrow ranges of experimental

parameters, to describe them over extended ranges requires

some form of detailed mechanism. There was considered to be a real need to understand chemical mechanisms and to measure rate constants for elementary reactions.

The relationship of elementary reaction rate data to the modeling of practical combustion systems received

further consideration during the general discussion period. Edelson (7-2) questioned what would be the impact of the better measurement of a particular rate constant in a complex reaction scheme for a combustion model in which the chemistry is summarized in a few reactions. Engleman (7-3)

32
pointed out three areas in which chemical kinetics can contribute to combustion research: defining the problem,

expanding the data base, and arriving at a solution. Keck

(7-4) recommended that laminar flame speed data be used as

a critical test of the predictive capability of combustion

models. It was pointed out that flame speed is directly

related to flame thickness and to quench layer thickness,

and that flame speed measurements are needed for practical

fuels at high temperatures and high pressures. For this topic also, the view was reiterated that we must understand

the basic mechanism and know the rate constants for the elementary reactions.

Dean (7-6) and Fontijn (7-8) addressed the general

question of the usefulness of kinetics research. They were optimistic. Kinetics data can find quick practical

application, as has been shown in rocket exhaust combustion

studies, and in atmospheric pollution. The kineticist has

a definite role to play. He studies the complexities of the system in order to guide the modeler in developing

simplified mechanisms. Also, with an effective

modeler-kineticist feedback loop emphasis can be placed on improving the critical kinetic data and the essential

mechanism

In the second invited talk, Hartley discussed advances

in laser diagnostics for combustion research. He pointed

out that optical scattering techniques are useful for their ability to make time dependent measurements on small regions of space without the disturbance normally

introduced by physical probes. A number of techniques were discussed to introduce chemical kineticists to the possibilities of using them in their own research. After this talk there was some discussion of whether

or not the information that could be obtained by the diagnostic techniques planned for the Combustion

Diagnostics Facility would be sufficient to unravel the chemistry occurring in the system. Myerson (7-5) recommended that the techniques to be used in this facility

should not be restricted to those using lasers, but that other techniques, especially fast broad-spectrum infrared diagnostics should also be used.

The general discussion led by Dryer and Glassman

focussed on the research needs in high temperature kinetics

research. Glassman opened the discussion by noting that we know enough of the overall mechanistic characteristics of most fuels to be able to burn them efficiently. The new dimension arises from the environmental constraints that

33
now exist. Factors such as sulfur and nitrogen emission,

and soot formation have become major concerns in combustion

research. A discussion outline was then presented in an attempt to concentrate attention on combustion problems

considered by the discussion leaders to be important. (The detailed outline is printed immediately before this summary.) These current combustion problems were categorized as follows;

1. Aromatics - pyrolysis and oxidation.

2. Soot and polycyclic aromatic hydrocarbon formation.

3. Heterogeneous kinetics, quenching, probes, catalysis

4. Alternative fuels - thermal and oxidative stability.

5. Sulfur oxidation kinetics.

6. NOx formation - reactions involving fuels.

7. Aliphatic oxidation - mechanism and rates.

8. Ignition, initiation and induction periods.

Apart from the topics of NOx chemistry and aliphatic

oxidation, these are topics that have not been studied in detail by many kineticists. The main result of the discussion was to alert the kinetics community to the need

for work in these areas.

It was generally considered that, at present, it is not possible to predict the kinetics of aromatic systems

and that working out the details of the mechanism and kinetics will take perhaps a decade. However, it was felt that sufficient experimental tools are available to begin

attacking the problem.

A generally similar situation was considered to exist

in the area of soot formation. There are not reliable rate data for nucleation reactions. But there are strong

similarities in the oxidation of soot and graphite. It was pointed out that in the combustion of some polymers, soot formation is reduced upon addition of transition metal oxides. The mechanism is unknown, but is being

investigated. Fontijn (7-7) pointed out that soot formation is being studied and listed several investigators

.

There was very little discussion of the subject of heterogeneous kinetics, although it was felt to be important to study heterogeneous reactions so that their effects could be differentiated from homogeneous reactions

in experimental chemical systems and practical combustors.
Also there was very little discussion of the subject

of alternative fuels. The point raised by the discussion

leaders was that fuels derived from oil should show changes

in viscosity and even solidification during storage.

The current status of our knowledge of the low temperature sulfur oxidation reactions was summarized. It was pointed out that the oxidation of divalent sulfur by 0 or OH begins with an addition mechanism which is known only

at low temperatures and cannot be extrapolated to e.g. 2500 C. It was pointed out that the conversion of S02 to S03 is not yet understood.

NOx formation and reduction were the subject of considerable discussion. Bowman (7-9) emphasized that NOx emissions . are kinetically limited and discussed the present

state of knowledge of NO formation kinetics. He stated

that we know well enough the rate constants for the reactions forming NO from atmospheric N2 (the Zeldovich

mechanism) and that any inadequacy in our ability to predict the formation of NO by this mechanism is related to our inability to specify adequately the environment

(temperature, 0 atom concentration, etc.). However, this mechanism does not predict the behavior of NO formation in fuel- rich flames or in fuels containing organic nitrogen

compounds. He stressed the need for a coordinated research program in the chemical kinetics of conversion of fuel nitrogen to NOx and pointed out as specific research needs

the determination of the mechanism and kinetics of the following reactions: reactions of hydrocarbon fragments

(e.g., CH, CH2) with N2, the initial breakdown of fuel-nitrogen species, reactions of N-containing

intermediate species (HCN, NH, NH2, CN) found in flames,

reactions of NO with N-containing intermediates and fuel fragments, and lastly the suggested interaction between NOx

and SOx in flames.

It was suggested that the possible attack on atmospheric N2 by the radical C2H must also be considered

on the basis of a revised value of its heat of formation

and newer data on the concentration of C2H2.

A recent study correlating the concentration of HCN in fuel-rich flames with the concentration of CH and CH2 was mentioned. McLean (7-10) noted that studies of the production of NO from fuel nitrogen have shown NO formation

and destruction reactions to be simultaneously important.

35
Myer son (7-11) pointed out that the rapid reactions of these same hydrocarbon fragments with the NO produced must

also be considered. Laufer (7-12) discussed results of a recent study of the reaction of CH2 with N2 indicating that formation of the spectroscopically observed HCN must proceed through a "long-lived" intermediate and is not the result of a simple reaction scheme involving N2 and either

CH or CH2 . In this connection, Lin (7-13) pointed out that although the direct reaction of CH with N2 to give HCN + N

is "spin-hindered", this hindrance is expected to be considerably less if the intermediate complex is stable and long-lived , analogous to some 0 (ID) quenching reactions. Dorko (7-14) stated that research on organic nitrogen

compounds is needed in order to devise methods for bypassing purification procedures.

It was generally agreed that the subject of aliphatic

oxidation is not well understood; we don't even completely

understand methane oxidation. In particular, the nature of formaldehyde dissociation, and methyl radical reactions

with molecular oxygen needs clarification. Gelinas (7-15) felt that there is a need for simultaneous measurement of all possible flame species to yield sufficient information

to allow discrimination along various chemical mechanisms.

Gann (7-16) discussed the effects of additives on combustion systems with emphasis on flame inhibition

studies involving halogens and metal atoms.

In summary the main result of the first day's

discussion was to point out to the kinetics community the need for fundamental research in areas not yet studied in detail

.

References

1. Dryer, F.L. and Glassman, I. "High-Temperature Oxidation

CO and CH4 " Symp. Comb. 14th (Combustion Institute,

Pittsburgh, 1973) 987-1001.

36
6. DISCUSSION OF ACQUISITION OF HIGH TEMPERATURE KINETIC DATA Discussion Leaders: S.W. Benson, Univ. of So. California

D. Gutman, Illinois Institute of Tech.

6 . 1 Outline for the Discussion

The combustion of fossil fuels probably involves every category of elementary gas-phase reactions known as well as numerous heterogeneous processes. The successful modeling

of practical combustion systems requires three kinds of information. First, a broad pool of general knowledge on many classes of elementary reactions is essential to have a reasonable basis for deciding which kinds of reactions

should be included in the mechanism of the process under study. Second, thermochemical information on reactants,

intermediates, and products is needed to calculate equilibrium constants and estimate rate constants. This information can be used to identify those reactions in the mechanism of the process under study for which accurate Arrhenius parameters are needed for reliable predictive

purposes. Thirdly, for key reactions, accurate rate constants are needed at all temperatures occurring during

the combustion process. Knowledge of mechanism changes

with temperature as well as pressure and temperature

changes in the rate constants of important unimolecular processes must also be available.

As a framework for the discussion on Acquisition of High Temperature Kinetic Data it would be useful to discuss

chemical reactions important in combustion by classes defined more or less by the methods used to study them since future studies of reactions within each group will

face similar experimental problems and limitations. Questions which will be raised and hopefully answered for each category of reaction should include the following:

1. Among the current means of isolating the reaction of interest for study, which provide the most useful and reliable rate constants and mechanistic information?

2. How can current methods of studying these elementary

reactions be improved to be either more reliable or more accurate?

3. How can new and emerging analytical methods and experimental procedures be used to develop fresh approaches

to studying these gas kinetic steps?

37
4. What thermochemical information is most needed to calculate Ar rhenius parameters for this kind of reaction

and how can it be obtained?

5. What specific reactions might have a higher priority

for study in order to obtain the most useful information

for practical modeling of combustion processes?

6. What value do studies performed below 500 K have for predicting mechanisms and rate constants at combustion

temperatures (say 2500 K)

?

7. What are "areas of exploration" which might offer new insights into various aspects of combustion including

ignition, rate of heat release, formation of major

pollutants (such as NO, S02 , and soot) and the formation

of trace amounts of highly undesirable products? Classes of Reactions Important in Combustion Processes

1. HIGH ACTIVATION ENERGY REACTIONS (EA>15 kcal/mole) - reactions with high activation energies control ignition delays, rates of branching, and changes of mechanism with temperature,, In spite of their importance, little is known about many because such reactions must be studied at very high temperatures,

often under nonisothermal conditions, and usually in systems where secondary and tertiary reactions cannot

be suppressed . These reactions can be subdivided as follows

A. PRIMARY INITIATION - In an oxygen rich environment

primary production of free-radical intermediates

probably proceeds to a great extent by the reaction,

Fuel + 02 -> 2R. (e.g. CH4 + 02 -> CH3 + H02)

It has not yet been possible to study such reactions

directly. What information is available is largely

derived from induction-time measurements in shock-heated fuel + 02 mixtures*

B. PYROLYSIS OF MOLECULAR REACTION INTERMEDIATES - The pyrolysis of peroxides, aldehydes, and other oxygen-containing products play key rate-determining

roles in low temperature combustion and in the transiton to high-temperature burning. A considerable

33
amount of information is available from bulb experiments on the pyrolysis of larger organic

molecules, and from shock-tube studies on the pyrolysis of H202 and simple hydrocarbons. Gaps in our knowledge should be identified, and the role of absolute rate theory calculations of rate constants

should receive special attention.

C. PYROLYSIS OF FREE-RADICALS - The pyrolysis of chain- carriers is largely responsible for the change in combustion mechanism with temperature.

Although there is some knowledge of the mechanisms,

branching ratios and rate constants for the pyrolysis of alkyl radical little quantitative

information is available on the rate constants for the pyrolysis of peroxy radicals (e.g. CH302 -> CH3 + 02) , acyl radicals and alkoxy radicals. For many of these intermediates internal rearrangements

occur at elevated temperatures complicating the kinetics picture.

Virtually all our limited knowledge of the rate constants for these processes come from indirect

observations. Should special attention be directed

at developing methods of detecting and directly

measuring the rate constants of reactions involving

polyatomic free radicals?

D. ATOM TRANSFER REACTIONS INVOLVING ALKYL RADICALS

with 02 - Although reactions of the type,

R. + 02 -> olefin + H02, and

R. + 02 -> RO. + 0 are known to be important in high-temperature

combustion, and it is known that rate constants for these reactions are essential for combustion

modeling, still essentially no quantitative

information exists for either of these processes. What methods might be applied to isolate these processes for quantitative study?

2. MODERATE ACTIVATION ENERGY REACTIONS (2 kcal/mole<EA<10

kcal/mole - This category includes the chain-carrying

transfer reactions responsible for heat release, some chain branching, and product formation.

3^
A considerable body of information exists on atom-exchange involving H, and 0 atoms due to the ease

in generating them under controlled conditions, the ability to detect these atoms at low concentrations and

the fact that they can be studied in pyrex or quartz vessels or in flow reacttors. An increasing body of equally accurate information on OH-r ad icals is becoming

available

.

Most rate constant measurements do not extend

above 500 K. Should more attention be directed at developing extrapolation methods to obtain

high-temperature rate constants? How can accurate rate constants be measured above 500 K. There is still a dearth of quantitative knowledge

on the atom-transfer reactions of the more complex

chain carriers present in the low-temperature

combustion zone, reactions of alkoxy, alkylperoxy, and acyl radicals and to a lesser extent the reactions of alkyl and hydroperoxy radicals. The problem is, of course, that it is difficult to produce these intermediates under controlled conditions and also to detect them at low concentrations. Again an important

question is what special methods can be developed to study reactions of polyatomic free radicals more directly and more quantitatively?

ADDITION AND RECOMBINATION REACTIONS (0 kcal/mole)<EA<5

kcal/mole) - addition reactions such as,

R + 02 -> R02, and H;0;OH;R + alkenes , alkynes <-> Adduct -> Products

are important radical-chain processes and are relatively easy to study even at room temperature

because of their low activation energies. Studies of 0 and OH reactions with unsaturated hydrocarbons reveal

the energy rich adduct can decompose in many ways, making identification of reactive routes and determination of branching ratios important. Changing

Arrhenius parameters with temperature suggest mechanism

changes as the temperature is raised. It would be useful to study the mechanism and rate constant changes

of representative reactions from room temperature to 2500 K to provide accurate data on such transitions.

40
Hopefully the behavior of analogous reactions could

then be calculated from the knowledge gained from such

stud ies

.

There is a large body of knowledge on the recombination rates of many free radicals, but lesser knowledge of disproportionation branching ratios and

their temperature dependencies. Here again new experimental approches are needed to extend the body of knowledge in this area. HETEROGENEOUS REACTIONS - The loss of free-radicals on aerosol particles early in combustion and on soot during late combustion deserves discussion. If these processes are important, how can they be quantitatively

studied?

41
6.2 Summary of the Discussion

M . J. Kurylo and W. Tsang

The general tenor of the discussion during the second day on aquisition of kinetics data was dictated by the two invited papers [Golden, and Garvin and Tsang] and a detailed preview by the discussion leaders [Benson and Gutman] on the important classes of combustion reactions

which must be attacked, In the following we summarize

these talks and follow with the main points raised during

the discussions.*

Golden began his review by demonstrating the immense number of reaction processes that must be known if a complete kinetic model of combustion processes is to be constructed. Exact measurement of all the reactions is clearly impossible within realistic time constraints. Thus algorithms for scaling, extrapolation, or prediction of rate parameters across reaction conditions and classes of reactants provide the only possible means of satisfying the ambitious data needs. Transition state theory using

thermochemical kinetics as a calculational tool appears at present to be the only method which gives a prescription

for constructing such rules. Golden illustrated its utility with applications to systems of importance in combustion contexts. He emphasized the need for supporting

this approach through improved measurements on thermochemical properties of free radicals, radical termination processes, NOx formation reactions etc. Golden pointed out that although transition state theory is an equilibrium kinetic theory, PPKM calculations provide a basis for estimating departures from equilibrium behavior

when energy-exchange effects are manifested in fall-offs

from unimolecular behavior or in the reverse bimolecular

process. He demonstrated the power of this approach with examples from atmospheric reactions and indicated that at the higher temperatures in combustion systems such effects

could be expected to be much more important. Key

parameters for such calculations were third body

efficiencies and the structure of the transition states. Developments in these areas were summarized. Statements made during the discussion are attributed to individuals only if they submitted written comments. For those cases, references are given to numbered comments in Section 7.

42
In the subsequent discussions the equilibrium nature of transition state theory was reiterated by several speakers.

Kwei (7-17, 7-18) pointed out that inasmuch as combustion

systems frequently display large departures from thermal equilibrium the entire basis for the use of such calculations under these conditions must be regarded with caution. Furthermore he noted that although transition

state theory can frequently fit experimental data,

questions regarding applicability and uniqueness remain. Thus uncertainties regarding predictive and extr apolative

powers must still be considered. He suggested molecular

beam experiments as a means of settling ambiguous points.

In a similar vein the possibility of checking transition

state predictions with the results of quantum mechanical

calculations was presented and mention was made of such efforts on the reactions 0 + CH4 and OH + CO. Shaw (7-19) on the basis of his experience in correlating data on radical abstraction process recommended an empirical rate relation. Unfortunately, this formulation was at variance

with transition state predictions. Skinner (7-20) was doubtful of the usefulness of the transition state approach

as a predictive tool. Instead he saw a more limited role

as an interpola tive tool, especially among compounds of a particular class. As such it might play a particularly

useful role as a basis for characterizing complex systems

in terms of the reactivity of a small number of active

groups. For the advocates of transition state theory the claim was made that entropies of activation could be so accurately calculated that, given a rate constant, the activation energy might frequently be calculated quite

accurately. With respect to curvature in the Ar rhenius

plot, the suggestion was made that, since rate constants at lower temperatures are more sensitive to this effect, measurement under such conditions (< ambient) should provide a more unambiguous basis for extrapolation to higher temperatures. This is undoubtedly true, however for the large temperature ranges to be covered changes in reaction mechanisms could bring in other processes.

Finally, there was a discussion on the format for presenting the results of RRKM calculations. The general

conclusion was that multiparameter fits can be easily made. However modelers indicated a preference for simple function

strictly defined within limits of applicability.

Garvin and Tsang (in their paper) defined the most important elements of a combustion kinetic data base as the rate constants for elementary gas phase reactions involving

the pyrolysis and oxidation of hydrocarbons and assorted pollutant related compounds at elevated temperatures.

43
Concentration on this type of data was due to the transferability of the information, the ubiquity of the processes in all combustion contexts and the existence of considerable information. They recognized that a complete

data base should also contain state to state, heterogeneous

and condensed phase data. However the underdeveloped

nature of these subjects rendered their inclusion

difficult. Global reactions should be derived from elementary rates. Their non-tr ansfer abil ity suggested that inclusion in a general data base would not be worthwhile.

Statistics on the production of high temperature kinetics data showed a constant or slightly declining rate during

the past decade. This was in contrast with the rapid

increase in measurements near ambient conditions (from

pollution concerns) . The successes in this area suggested

that applications of the newer techniques to high

temperature kinetics with a corresponding increase in activity would yield important information. Sources of evaluated kinetics data were listed and the advantages of a sole-source data base indicated. In agreement with Golden,

they noted the immense volume of data needed and suggested

strong experimental efforts on those reactions of importance in predictive and correlative schemes. A variety of these schemes was summarized. With respect to data accuracy, the importance of base point reactions in relative rate determinations was recognized and recommendations were made for definitive studies of these rates. The possible contributions from chemical kinetics

modeling toward the building of the data base were discussed. These involved the identification of key processes and the unraveling of complex experiments. In both cases sensitivity analysis would play a key role. The subsequent discussions focused principally on the proper use of chemical kinetics data in modeling. Many of the comments were based on participants' experiences with modeling the methane oxidation system. Some specific

problems with respect to rates and mechanisms were mentioned. There was disappointment with past progress in this area and agreement that the blind use of extended

lists of rate constants would not not be useful

[Bauer (7-21), Hyerson (7-22) and others]. Keck (7-4) suggested that useful results are not achievable in the near future, Bauer (7-21) and Gelinas (7-36) outlined

possible procedures that might reduce the number of reactions considered to those which were truly meaningful.

The need for proper procedures for sensitivity analysis

was made clear. Gelinas (7-23) warned that reaction

mechanisms may change with time regions. Indritz (7-24) pointed out that in eliminating a reaction one has set its rate constant at zero. Myerson (7-22) deplored the all too

44
easy tendency to simply fit the data over limited ranges. Engleman (7-3) suggested that the kineticist's role should

be more than supplying rate constant and that they may be able to make important contributions to problem

definitions. Thus there was general agreement that the "present Laissez-faire approach which required at least two decades to home in on a reasonable mechanism for methane"

Bauer (7-21) was unsatisfactory and there is a need for procedures in data analysis.

With respect to methane - oxidation the possible consequence of Golden's statement in his earlier

presentation that he was unable to detect products from the CH3 + 02 reaction under Very Low Pressure Pyrolysis

conditions at 1000 K was challenged by several participants

on the basis of shock tube data. Possible means of reconciling the apparent conflicts were suggested. Other problem areas in the data base for methane oxidation

include formaldehyde decomposition and formyl radical reactions. It was made clear that the quantitative details

of the methane oxidation process remain uncertain. Finally

Westley (7-25) mentioned the uncertainty in data on pyrolysis brought about by possible presence of trace quantities of oxygen.

Prior to the discussion session on high temperature data acquisition, Benson gave a general review of the interrelation of chemical kinetics, combustion and the energy crisis. In particular he highlighted the possible

key roles of alkylperoxy radicals in flame propagation. Gutman continued the discussion preview by presenting a systematic picture of the various classes of combustion

related reactions that must be studied (i.e. initiation,

branching, propagation, and termination). In each of the classes, the existing uncertainties far outweigh the knowns when we depart from the old familiar oxygen-hydrogen and oxygen- methane systems. He suggested, however, a variety

of experimental tools which may prove useful for solving

these difficult problems. Particular emphasis was placed

on laser-based techniques and their possible role in the the generation, detection, and kinetic measurement of unstable polyatomic species. He challenged the experimentalists to apply the new methodology not only to rate constant measurement but to mechanistic delineation as well. Here again particular emphasis was placed on the present lack of information (or means to obtain it) on organo-peroxy and organo-oxy radicals.

45
Gutman stressed the importance of a careful mechanistic

sensitivity analysis in the interpretation of complex

experimental results. The use of a common data base for such calculation was mentioned as being a particular

necessity.

Workshop participants took up the challenge of Benson

and Gutmann and presented a variety of technologies which they were presently using or proposed as useful for performing high temperature combustion diagnostics and/or kinetic measurements. Many of these replies appear as written comments by the participants and are cited below. Bauer (7-26) described some recent experiments

employing a laser- Schlieren technique (post shock front density gradient technique) for making measurements on shock front gradients during the dark (induction) periods

of hydrocarbon pyrolysis and oxidation. Using this method,

one examines the exo- , endo- thermic balance immediately

after the shock has passed through the system. A cautionary note was added that one should be concerned with gas dynamic instability due to very exothermic processes.

Other comments affirmed the presently accurate temperature

characterization in shock heated systems. Keck suggested a similar type of measurement facility in the spherical

combustion bomb. He outlined the use of pressure transducers, ionization probes and laser diagnostics to observe flame front profiles following ignition. He further stressed (7-27) the importance of making measurements at high gas densities where many of the rate controlling processes change from tr imolecular to bimolecul ar in character. Tsang's recommendation (7-37) that attempts be made at minimizing the number of ongoing reactions in such systems

to simplify interpretation underscored his advocacy of the single pulse shock tube technique. With such an apparatus,

all but the initial reaction can be eliminated (by low reactant densities) thereby yielding very detailed

mechanistic information. He suggested that under well defined initial conditions, one can "bootstrap" his way through the various stages of complexity.

These same preferences were echoed by Myer son (7-28) who envisioned the single pulse shock tube as an excellent

technique for obtaining the needed kinetic data on pyrolysis and combustion of aromatic and coal- relevant

46
molecules. In addition, he cautioned the researchers not

to abandon these older methods of combustion analysis for the alluring charm of total laser diagnostics, but rather approach the problems with the full armament of measuring

techniques

.

Kern offered still another shock tube-associated

technique in the use of time of flight mass spec trometr ic sampling of reflected shock zones. Such experiments have

had applicability in the measurement of precursors to soot formation and the identification of chemi-ions.

Skinner (7-29, 7-30) presented an extensive list of measurement techniaues and discussed their applicability

for combustion studies. More specifically he, too, advocated the use of shock tube studies in order to work up gradually in the complexity of systems thereby allowing modelers to check out a complete kinetic subsystem apart

from transport phenomena.

Eogan (7-31) and Seery (7-32) pointed out the versatility of molecular beam sampling mass spectrometry

for probing both stable and unstable species in high

temperature combustion systems. Such an apparatus coupled

with optical diagnostic techniques appears useful in probing complex systems as well as studying isolated reaction processes. Benson briefly outlined recent experiments performed

using a very low pressure pyrolysis reactor for controlled

free radical production. While limited in temperature

range, this technique promised to be useful in getting some first data on a number of radical-radical interactions as well as radial heats of formation. Brink's comment (7-33) solicited the inclusion of dye laser intracavity absorption as possible diagnostic for studying combustion reactions. Its high sensitivity and good spectral fidelity make it a viable candidate.

A still newer laser technique was described by Huie

(7-34) who has utilized infrared mul tiphoton

photodissociation to produce cleanly organic radicals (viz. CF2) . Combination of this production technique with mass

47
spectrome tr ic detection should prove useful in planning controlled radical kinetic studies at high temperature.

Livingston related some recent sucess in using ESR to detect short lived free radicals produced thermally in fluids. Present capabilities allow for pressures up to 75 atmospheres and temperatures approaching 800 K. A planned extension of the flash photolysis resonance fluorescent techniques to nearly 2000 K was described by

Fontijn (7-35) . The original technique has been proven to be quite versatile by many workers in measuring radical and atom reactions from 170 K to 500 K using real time fluorescence detection. Incorporation of this type

facility in a furnace should permit for the first time the direct measurement of many elementary reactions at temperatures of interest to combustion modeling.

Along similar lines, the usefulness of pulsed

radiolysis techniques to produce free radicals in controlled kinetics experiments was related and measurements made using this technique were summarized

(7-38). Present capabilities allow pressures of up to several atmospheres. It is planned to extend the temperature capability to at least 1000 K.

48
7 . Contributions Submitted by Participants

The participants at the meeting were encouraged to write down comments they made at the meeting and were given

the opportunity to submit others afterwards. Many did so. These comments are printed in this section, aproximately in the order in which they are referred to in the summaries of the discussions, sections 5.2 and 6.2. In general, this means that comments on particular topics appear near each other. Comment references in the Summaries lead the reader

to this section. An author index for this section follows

the comments.

49
7-1 Topic: Necessary Elementary Data for Modeling.

C. Westbrook, Lawrence Livermore Laboratory. Many kinetics

phenomena may be modeled from elementary rate data alone, but there are many more which are characterized by a close coupling between kinetic and spatial transport processes.

In such environments observable results depend upon single

particle transport rates through mul ticomponent gas mixtures. There is a wealth of kinetic data, which is available from good flame experimental data, but to be approached by modeling these transport coefficients must be known to within the same uncertainties as the rate data, if not better. I suggest that a proper function of a data

base in this area would be to include data and evaluations

on binary diffusion coefficients for different chemical

species. Modelers can use this data to estimate

multicomponent diffusion coefficients if necessary, but the binary diffusion coefficients into a variety of component

species are needed in these transport models. Although

these coefficients can be estimated from kinetic theory

arguments, it is likely that molecules with many internal degrees of freedom may not diffuse in a simple way, so that experimental data are needed, and these data should be evaluated by someone who can do so properly.

7-2 Topic: Needs for High Temperature Kinetics Research.

D. Edelson , Bell Laboratories . One of the major areas of uncertainty is the relationship between fundamental chemical kinetics on the one hand and the state of the art

in computer simulation of combustion systems on the other.

At the present time the latter is limited to the consideration of "global" (lumped) chemical models because

of the prior necessity of treating the very complex fluid and thermal transport of any real combustion system. Because the chemistry provides the driving force for the fluid dynamics, it is not clear whether a separation of the chemical and transport computations is possible, since neither can be considered a small perturbation on the other . In this light, it is very difficult to assess the impact

which the detailed study of any particular phase of the fundamental chemistry can have on the overall problem.

Beyond a qualitative grasp of the important features of the chemical mechanism, i.e., whether a class of reactions does

or does not take place, it becomes questionable whether

50
efforts at quantifying particular steps is worthwhile. Advances in the techniques of modeling these complicated processes are required if these fragments are to be assembled into a coherent picture. New machines, and new methods in numerical mathematics are becoming available

which could profitably assist in resolving these difficulties. Efforts should be made at gradually

supplanting the present use of simplification and approximation methods with more exact calculations. As this is done, then a complementary requirement for improved

kinetic data will become apparent, and will point the direction for future research.

7-3 Topic: Needs in High Temperature Kinetics Research.

V. Engleman , Science Appl ications Inc . Chemical

KTneticists can make valuable contributions to combustion research in three areas:

(1) Defining the problem - identifying the key

phenomena and establishing a plausible mechanism.

(2) Expanding the data base - sensitivity studies

and obtaining improved kinetic information on key reactions.

(3) Arriving at a solution - narrowing down the mechanism to a tractable size and perhaps

arriving at meaningful global or semi-global

rate expressions, recognizing that this step is problem dependent . Specific combustion problems are at different stages of need. Coal combustion/gasification is still at stage 1. Methane/air combustion is generally at an advanced stage 2. And portions of the methane/air combustion problem are ready for stage 3. The kineticist should play a key role in the problem

definition (stage 1) and should work closely with the modeler, especially at that stage.

It should be recognized that stage 2 is a continuing effort

(improving accuracy of rate constants) and can be long-term. Stage 3 should proceed during that process.

51
The chemical kinetics problem is not solely in determining

reaction rates even though that is an important activity. Overall problem definition and problem resolution need the guidance that can be provided by the kineticist.

7-4 Topic: Combustion Modelling

J. C. Keck , Massachusetts Institute of Technology. Among

the most important combustion properties required for practical applications in engines and combustors burning

premixed charges are the laminar flame speed, laminar flame thickness, wall quenching distance, ignition energy and spontaneous ignition limits at densities from roughly 1 to 100 atmospheres. The prediction of those properties from first principle is an exceedingly complex problem requiring

both a knowledge of a large number of ill defined reaction

rates and the numerical solution of a large system of coupled rate and diffusion equations. The probability that

such a synthesis will lead to quantitatively useful (+ 20%) results in the near future is extremely remote. It is therefore important that the direct measurement of the fundamental combustion properties listed above be included

as an integral part of any basic chemical kinetics program

related to combustion. This would serve the dual purpose

of providing a critical test of the predictive capability

of the synthetic approach as well as making immediately

available essential information required for practical

applications. In this regard it could be noted that laminar combustion properties are also useful in turbulent combustion for predicting turbulent flame thickness,

ignition energy and wall quenching distance, in cases where

the turbulence scale is large compared to the laminar flame thickness.

7-5 Topic: Combustion Diagnostic Facility - Infrared et al

.

A. L. Myer son , Exxon . It is rather perplexing to understand why this facility which I understood was to be

for general use, seems to be completely dominated by

scattering techniques and/or those which use lasers. With

the advent of a major stress on more complex hydrocarbons

(aromatics, et al . , from coal etc.), and the availability

of fast, broad spectrum infrared diagnostics, at least the latter techniques should be a significant part of the facility. Other techniques should include: ARAS, laser densitometry, single-pulse shock tube analysis, etc.

52
7-6 Topic: Impact of Chemical Kinetics on Combustion Research.

A. M. Dean , University of Missour i-Columbia

The kineticist can provide information about the elementary

chemical reactions and the associated rate constants for a particular combustion system. This information is vital to the combustion modeler even though it is often too detailed

for practical combustor calculations. The importance of the mechanistic information is that, for a sufficiently

detailed mechanism, it should be applicable over a wide

range of conditions. The modeler can then make the necessary simplifications for his particular application

and check the accuracy of his approximations against the complete mechanism. In this respect the role of the kineticist can be viewed as one who attempts to understand

all the complexities of the system so that modelers can have a guide as to what constitutes a valid simplification

for a given situation.

7-7 Topic: Soot Formation.

A. Fontijn , AeroChem Research Labs . Activity in this field

is too low relative to its importance, but it is incorrect

to state that no kinetic studies are performed.

At AeroChein Calcote and Miller are studying ionic mechanisms in soot formation. Other important activities

are going on; Dr. Jack Howard at MIT and Dr. Bill Shipman at Cabot Corporation (carbon black) can give

information on some of these.

7-8 Topic: When will the new kinetic data that we can generate

become of practical use?*

A. Fonti jn , AeroChem Research Labs . Many pessimistic

remarks on this subject have been made this afternoon. More optimistic notes were sounded by those involved in the stratospheric pollution problem. However, there is direct

evidence as well in the combustion area that the right type of kinetic data can find quick practical application.

Prime examples here are rocket exhaust combustion problems,

a field of major interest ten to twenty years ago and on a lesser scale still today. Modeling studies are a common

•approach here and the interaction between the modelers and kineticists has paid off handsomely. The type of

53
interaction required is, of course: (i) kineticists make

their best guesses as to rate coefficients (ii) modelers

incorporate these and establish which reactions are the most important, (iii) kineticists measure these, and (iv) the improved model is used by design engineers and by

kineticists to determine if, and which, further reactions

need study.

7-9 Topic: Chemical Kinetics of NO Formation in Combustion

C. T. Bowman , Stanford University. Environmental

considerations place significant constraints on nitrogen

oxide emissions from combustion systems. The trend toward

use of fuels containing significant quantities of organic

nitrogen compounds will make control of NOx emissions more difficult. To support development of NOx control techniques, including combustion modification and combustion gas clean-up by injection of reactive additives,

a co-ordinated research program in chemical kinetics of conversion of fuel nitrogen to nitrogen oxides is required.

Some specific research needs include:

1. Determination of the mechanisms of reactions between hydrocarbon fragments and molecular nitrogen. What are the reaction products? What are the relevant rate coefficients?

2. Determination of the mechanisms of initial breakdown of fuel nitrogen species. What are the reaction products? Does the relative importance of various reaction paths change in the presence of oxygen? Are there common intermediate species?

3. Determination of mechanisms and rates of reaction of nitrogen-containing intermediate species found in flames (HCN, NH, NH2, CN) . These species appear to play a significant role in the NO formation process.

4. Determination of mechanisms and rates of reactions between NO and nitrogen-containng intermediates

and fuel fragments. These reactions play a major

role in NO removal in the flame zone and postcombustion gas.

5. Study possible interactions between NOx - SOx in flames. There is some evidence to suggest that the presence of sulfur compounds reduces NO formation from organic

nitrogen compounds in flames.

54
7-10 Topic: NOx Formation and Reduction

W. J . McLean , Cornell University . The argument that in the fuel nitrogen problem we should emphasize studies of the NOx reduction reactions rather than the formation reactions

needs some clarification. While it is true that NOx forms quite fast from fuel nitrogen, it is not necessarily true that the formation and reduction processes can be separated

and studied independently. A number of studies reported in the literature indicate that the fuel nitrogen mechanism

involves NO in a dual competitive reaction path. That is, NO is simultaneously being formed from some nitrogeneous

intermediate and converted in part to N2 by reaction with other single-N compounds. Our own studies of NO production

during HCN oxidation also indicate this general behavior,

and we find NO formation and destruction to be simultaneously important in determining the eventual fate of the nitrogen.

Studies of the combined mechanisms for NO production and removal can assist combustion technologists in choosing

operating stoichiometr ies and temperatures which maximize

conversion of fuel nitrogen to N2. 7-11 Topic: Nitric Oxide Reactions for NO control.

A. L . Myerson , Exxon . Although we have discussed the importance of measuring the chemical kinetics of nitric oxide formation and destruction, as needed for NO pollution

control, no mention has been made of one of the most important set of reactions in this respect. There is every evidence that no model can be made of steady-state or non-steady-state NO concentrations in hydrocarbon

combustion, without considering the fast reaction of NO with hydrocarbon free radicals characteristic of the relevant flames and explosion, viz.

CH + NO = CHO + N CH + NO = HCN + 0 These are exothermic, fast, are present both early and late

in hydrocarbon combustion flames and depend on the eguivalence ratio for their degree of importance. They are

also of considerable importance in the internal combustion

engines when NO reactions with wall hydrocarbon combustion

films take place reducing the NO.

55
7-12 Topic: Formation of NOx in Fuel-Rich Systems.

A. Laufer

} National Bureau of Standards . We have examined

the reaction of CH2 with N2 and directly observed the formation of HCN for which we obtained a temporal profile.

The experiment involved the flash photolysis of CH2C0 and analysis by vacuum ultraviolet absorption spectroscopy.

HCN has a well-characterized spectrum in this region. The major experimental observation is that HCN appears only

after several hundred milliseconds following the flash. The role of CH may be eliminated both on energetic and kinetic grounds. Energetically, by the incident

wavelength. Kinetically, if we use the slower of the two measured values for CH + N2, we find a 1/e time for the production of HCN of about 10 m sec - in disagreement with

observation. In a like manner, we may calculate the lifetime of either 1CH2 of 3CH2 in this system to be less

than 1 millisecond. Since neither of the obvious precursors can lead to HCN through a simple reaction

scheme, we are required to postulate a "long-lived"

intermediate which can slowly re-arrange qr decompose to HCN. A complete description of this wo ok will appear shortly in "Combustion and Flame".

7-13 Topic: Mechanism of NOx Formation.

M. C . Lin , Naval Research Laboratory . With regard to the mechanism of the CH + N2 reaction related to NOx formation,

I have the following comments: (a) Although the CH(X 2 n) + N 2 (X 1 2g

+

) -> HCN(X 1 2

+

) + N

(

4 S

3 / 2

) reaction is "spin-hindered", the hindrance (or f orbiddenness) is expected to be considerably less if the reaction

intermediate HC=N=N is stable and long-lived. The best examples of this are the relaxation of O^D^) atoms by N2 and CO. Both reactions are known to occur readily (1)

,

although they are apparently "spin-forbidden". (b) We have previously shown (via laser emission and reaction product

analyses) that the flash photolysis of CHBr 3 below 200 nm generated CH in significant quantities . (2) We plan to study

the reactions of CH and C2H (from Br C2H ) with various molecular species of importance to combustion chemistry.

An ArF laser (193 nm) will be used as a photolysis source

and a dye laser for the detection of transient species. The conventional flash photolysis method is probably too slow for the CH radical because of its great reactivity and

the initial long, blinding interference due to the flash.

56
1. R. F. Hampson and D. Garvin (Eds.)./ "Chemical Kinetic

and Photochemical Data from Modelling Atmospheric

Chemistry," NBS Technical Note No. 866, 1975.

2. M. C. Lin, Int. J. Chem. Kinet. 6, 1 (1974); J. Phys. Chem. 77, 2726 (1973); J. Chem. Phys. 61, 1835 (1974).

Topic: NOx Formation and Reduction.

E . A. Dor ko , Air Force Institute of Technology . Nitrogencontaining compounds . The mechanism, temperature, and pressure dependence of decomposition fragmentation and oxidation of nitrogen-containing organic compounds needs study to understand what occurs, in order to eliminate NOx pollutants without necessarily passing through a purification procedure (which is expensive).

In addition in the study of oxidation of aromatics,

pyridine needs to be studied as an analogous, aromatic,

nitrogen- containing system. At this point very little is known of these matters.

Topic: Simultaneous Measurements in Flames.

R. J . Gelinas , Sc ience Appl ications . Among very high

priority needs in combustion science are simultaneous measurement of major, intermediate, and minor species in flames, as a function of space and time. The emphasis

should be on tractable fuels in highly interpr etable simple

flame systems. I am aware of only the work of Biordi and of the group at Louvain approaching this objective. Such work is necessary to provide distinctive levels of information content which will allow elementary physical

and chemical mechanisms to be studied in more discriminating detail. In the absence of simultaneous measurements a superabundance of free parameters is unavoidable and the information content yields minimal discrimination of important detailed mechanisms.

7-14

7-15

57
7-16 Topic: Chemical Inhibition of Flame Propagation.

R. G« Gann , National Bureau of Standards

.

There is a need

to know where the "soft" spots are in the combustion

sequence, i.e., those places where a small quantity of an additive can drastically affect the global rate of fuel consumption, heat produced, etc. There is current evidence

that halogen or metal atoms can be additives of this type.

If we knew how they worked, we would know how to optimize

the selection of perturbing species. Thus the problem

requires bulk experiments to determine specific

super-additives (for a given desired effect) and to determine some character of the reactive processes

involved: e.g., is the effect temperature or pressure dependent? What is the result of systematically varying

the additive species, such as substituting a chlorine atom

for a bromine atom or a glycol for an alcohol? With the evidence, possible competing reactions can be identified,

the kinetics measured, and the magnitude of the effect corroborated (or not) by insertion into a detailed kinetic model or again by checking relative effects of two or more

additives. A specific example of this involves bromine

inhibition of flames. Several studies have led to the hypothesis that termolecular recombination rates are critical, and that H + Br + M -> HBr + M is a specific rate constant for which we need better data to proceed further. Clearly more of this specific isolation study is needed.

In the flame inhibition field, numerous halogens, metals

and organometallics have been studied and the "winners" identified. Further such studies are in progress.

7-17

Topic: Role of non-thermal process in combustion.

G . H. Kwei , Los Alamos Scientific Laboratory

.

I would like

to offer a word of caution on the use of equilibrium rate constants in the modeling of combustion processes. Since dense mixtures of gases, many of which are reactive, are involved, it is not at all clear whether or not thermalization will precede reaction. Even if thermalization is rapid, minor channels involving non-thermal processes could be very important in pollutant

formation, soot formation, and efficient combustion; such processes are clearly important in luminescence and ion-formation in flames.

58
Although it would be difficult to incorporate more complicated kinetics in present modeling calculations, a better understanding of the competition between energy exchange and chemical reaction and of the role of non-thermal processes is absolutely essential to our understanding of combustion processes. If we do not have this kind of information, we may be modeling the wrong

system.

In order to meet this objective, we should identify a few key reactions and study (1) the dependence of the rate or cross section on reactant excitation (i.e.) under non-thermal conditions) and (2) the rates or cross sections

for de-excitation in collisions with molecules that are present in the combustion system.

7-18 Topic: Reliability of "Thermochemical Kinetics".

G. H. Kwei , Los Alamos Scientific Laboratory. Although Dr. Golden's inclusion of heat capacity terms in the

pr e-exponential factors has provided good fits to the experimental data for several reactions, it certainly is not clear that "thermochemical kinetics" would provide

equally good fits for all chemical reactions or that these techniques are reliable in the extrapolation of low temperature data.

Dryer and Glassman have obtained an equally good fit for the reaction of OH radicals with CO molecules by assuming

that the transition state has the same structure and vibrational frequencies as the stable HONO molecule. There

are two problems with this treatment: (1) Both intuitive electronic structure theory and experimental data on the pressure dependence of the rate constant suggest that this reaction proceeds via the formation and subsequent

decomposition of a long-lived complex and (2) our qualitative understanding of the electronic structures of HONO and HOCO suggest that neither the geometry nor the vibrational frequencies will be the same. Item (1) suggests that transition state theory is not applicable and item (2) suggests that even if it were applicable the quality of the fit will be affected. This raises the question of whether or not we are covering-up interesting

and important features of the reaction dynamics by fitting

the data to transition state models.

59
We are currently planning a crossed molecular beam study of this reaction as part of a larger program to study the dynamics of reactions important in combustion processes and

in atmospheric chemistry. Since both the collision energy dependence and the reactant vibrational state dependence

(for both reactants) of the reaction cross section will be determined, a much clearer understanding of this reaction

will soon be available.

7-19 Topic: Hydrogen Transfer Reactions.

R. Shaw , Lockheed Missiles and Space Company . Kinetics Measurements . Rate constants for the following reactions need to be measured above 2000K:

R + CH4 = RH + CH3 where R is H, O, HO, and 02. Kinetics Estimates . Existing, measured, rate constants need to be fitted

to k = AT2 exp (-c/t) for the reactions:

R + R'H = RH + R' (2) where R is H, 0, HO, aliphatic and aromatic and where

R' is aliphatic or aromatic. Thermochemistry.

We need more work on the heat of formation of CH3. 7-20 Topic: Correlation of Theoretical and Experimental Studies.

G. Skinner , Wright State University . At our present state of chemical knowledge it is unwise to use theoretical

methods, such as Thermochemical Kinetics, RRKM theory, or more detailed theories to make long extrapolations of kinetic data (such as from experimental data at 300-600K up to 2000K) unless there are some experimental data at the high temperatures on reactions of a similar chemical type

against which the theoretical method can be tested. In

'

60
general, we should try to get experimental data on at least one and preferably a few specific reactions which are representative of various types (such as reactions of 0 atoms with secondary hydrogen atoms on fairly large

hydrocarbon molecules). Once this has been done, theory

can be used to obtain rate constants for other similar reactions, to fill in any unstudied temperature ranges, and

to make moderate temperature extrapolations (such as 1500 - 2000K) . This approach enables us to work on the most easily studied molecules of a particular type, and therefore, to get the most accurate data, even if the easy or least difficult molecules are not those of greatest direct interest in combustion, since the theoretical methods can then fill in other molecules as needed.

It may well be possible to extend this method even further

in computer modeling. If, as may be expected, the rate constants of all reactions of a given type for larger

hydrocarbon molecules are about the same, the modeler may

not have to consider concentrations of the large number of different molecules that may be present, but only the number of reaction centers of a given type. This may greatly reduce the number of "species" and reactions. An additional parameter such as the average number of C atoms

per molecule would complete an adequate kinetic description

of a collection of hundreds of different hydrocarbon

molecules, such as one finds in gasoline.

7-21 General Comment , S. H. Bauer . There is agreement that were one to model combustion processes utilizing only one or two global reactions he may

arrive at misleading conclusions. At the other extreme, incorporating all of the conceivable reactions (hundreds)

is definitely not practical. Professor J. Keek's rational approach merits careful scrutiny. One cannot justify on operational grounds the use of extended lists of reactions when the amount of information provided by our experimental

probes is inherently limited, so that there is no feedback

from the laboratory to the model builder. I find it difficult to justify (relative to combustion theory) the expenditure of great effort in obtaining for some selected reactions very precise rate constants over limited ranges

of pressure and temperature, particularly when the reactions and the conditions of operation are selected on

the basis of convenience. One should demonstrate that the predictions for the system's behavior are sensitive to the

61
precise values. What is often missing is the prior

selection of the reactions which should be included or omitted for each range of operations of the combustor. The crucial question which we should try to answer, is there a better strategy available than the present laissez

f aire approach, which required at least two decades to home-in on a reasonable mechanism for methane? In my opinion the basic components for such a strategy are available but further work is required for their integration and optimization. I submit the following;

1. For any system it is possible to list all the significant participating species—atoms, radicals, and molecules which could be present in substantial, small, or minute concentrations. This is based on our present

chemical knowledge, and general "intuition".

2. For most species one can trust currently available

empirical relations for estimating their enthalpies of formation and entropies.

3 . It is then a straightforward calculation to estimate

the equil ibr ium concentrations of the species listed in (1) [for any range of temperature and pressurej

.

4. An algorithm has been written (W. M. Shaub and S. H. Bauer: will appear in Combustion and Flame) for a computer

to list all possible pairwise combinations (reactions) of the components on a list, so as to generate other members

in that list, subject to atom conservation. [Ternary

combinations of atoms or radicals appear as the inverse of binary dissociations]

.

5. For each reaction the corresponding AS,AH , AG are calculated

.

6. All reactions for which AG > a (some rational positive

value) are removed from the list.

7. Other simple criteria for removing unlikely reactions

have been programmed, such asAS either very large or very

negative, etc. However, beyond this stage we encounter the practical

crunch; How to program a computer so as to reduce the number of reactions (on the basis of rational kinetic criteria ) from the remaining several hundred by a factor of

10. Hence at this stage we need:

(a) Empirical procedures for estimating rate constants. These must include estimates of ranges of acceptable

values. Professor Benson has proposed a rational approach.

62
(b) Selection of critical observables for each system.

(c) Mathematical procedures for testing the sensitivity of the observables to the reactions which remain after applying steps (6) and (7), subject to the estimates in

(a) . For instance one may delete any reaction wherein the product of the rate constant by the equilibrium

concentrations of the reactants is below some lower set limit. This can be justified on the basis of the general

observation that the very reactive, unstable radicals

rapidly attain local-equilibrium levels, due to the multitude of chain reactions, and then drift along with the concentrations of the major species.

Dr. Gelinas mentioned three procedures now available for making such sensitivity tests. These should be explored in detail and further developed. Since I have not used them,

it is not obvious to me that any of these would be suitable when the specified error limits are large for a substantial

fraction of the rate constants as listed in (a). Nevertheless, I do believe that the problem is not insoluble, provided each of us takes a hard boiled attitude

regarding our favorite reactions: for any specified test

we should be ready to omit any reaction which does not significantly affect the predicted observables.

7-22 Topic: Computer Modelling of Chemical Combustion Systems.

A. L . Myerson , Exxon . I believe it is incumbent upon us to encourage those who mathematically model complex chemical mechanisms of combustion to maintain a more restrictive and realistic attitude. There is absolutely no justification

for including 50, 100 or even more chemical mechanistic

steps, if 50% of them are uncertain by an order of magnitude, 25% by 1/2 an order of magnitude and perhaps 10% by only 50% or 100%. It is too easy to match time-dependent phenomena at one temperature. The rules of the game must be made much more stringent than that. To some extent, a more precise outlook might be engendered by

adopting a "watch-dog" attitude in refereeing and reviewing processes.

6 3
7-23 Topic: Species Equilibration

R. J. Gel inas , Sc ience Appl ications . The question of when

individual chemical species are in local equilibrium (at a single local temperature) can be addressed by examining

individual species time derivatives, y^(x,t), which are described by differential equations of the form:

k

a y2, etc.) for individual reaction processes which produce

and destroy the i th chemical species at (x,t); and T. is th 1 the local rate of transport of the i chemical species at

(x,t) . For the present discussion, allow Ti to be zero or constant,, One finds that, as equilibrium is approached,

the individual forward and reverse reactions contained in the sets {p[(y) } and {L*(y) y^} come into balance. This occurs over relatively long time scales. When local equilibrium is finally approached, detailed balancing is achieved between each forward and reverse process, reaction

by reaction, at the local temperature 0(x,t).

Practically, the accession to local equilibrium can be readily observed by simply rank-ordering the P°(y) and

L*(y)Yj_ for all i species, as a function of time. At "early" times, individual forward and reverse reactions are scrambled in their order, and only a few such terms tend to constitute the y^'s. At "intermediate" times some forward

and reverse reactions are seen to approach each other in rank-ordering and in individual magnitudes, and the number

of processes constituting the y^ ' s is increasing. At large,

asymptotic times, all reaction pairs (forward and reverse) balance each other and y i ->0.

In this classic accession to equilibrium the magnitude of

y^ relative to individual Pj°(y) and L ia (y) y j_ terms also undergoes a systematic progression. At "early" times y^ is of the same magnitude as a few individual Pj°(y) and

L

1a(y) y_L terms. At "intermediate" times, y L is becoming

small relative to individual reaction terms (P^y) and

64
L^(y)y^) . In this interval y^ is generally determined by

the difference of an increasing set of competing P^y) and L*(y)y^) terms. At this stage detailed balancing has been

achieved by perhaps only one or two (if any at all) individual forward and reverse reaction terms. The other reaction terms have sizeable, but offsetting, magnitudes

which are still scrambled in rank-ordering. At local eguilibrium y^ becomes vanishingly small relative to the individual P^a and L*(y)y±, and detailed balancing is approached, reaction by reaction, at the local temperature,

9(x,t). Even the weakest individual reactions are required

to establish the final eguilibrium state.

To answer the original question, it turns out for most

simple combustion systems near atmospheric pressure

(.01-10atm), local equilibrium is approached only at times which are very long compared to flame induction,

propagation, energy deposition, and final product formation

times. Thus, equilibrium rarely exists at a single

temperature for most species at interesting times of flame evolution in the examples discussed today. Depending upon specific problem circumstances a fairly small number of reactions can suffice, or as many as 20-30 reactions may be needed to properly constitute the y^'s. Short-cuts are ill-advised. As a final note, it is quite possible for quasi-steady states to occur for some species at interesting flame evolution times; but this need not be synonymous with the existence of equilibrium at a single

temperature. Quasi-steady state can, and does, occur when

some y^ is "sufficiently small" relative to some larger

scale process over specified time scales, say, tq« In such cases, Tq may generally correspond to "intermediate" times discussed above, for which eguilibrium has not yet been established at a single temperature. Again, the number m of individual reactions needed to properly constitute the y^ '

s

over variable time scales is very much a problem-dependent

matter

.

As a footnote, the concept of multiple temperatures,

corresponding to effective equilibria for different

species, has often been suggested in non-equilibrium

physics and chemistry, but with little practical advantage

being realized either conceptually or computationally.

65
7-24 Topic: Use of estimated rate constants in modeling.

D. Indr itz , Princeton University . There is frequently

criticism of the use of rate parameters that are uncertain

in computer models. A point to remember is that omission

of a reaction is orders of magnitude more incorrect than any reasonable estimate would be. Omission of a reaction because its rate is uncertain is effectively including a rate constant of zero - orders of magnitude off. 7-25 Topic: Aliphatic/Oxidation in Very Rich Mixtures - Effect

of 02 and H20 on Pyrolysis.

E

.

Westley , National Bureau of Standards . I think that the "Outline of Needs" should include a statement showing

clearly and explicitly the difference between non-oxidative

pyrolysis and oxidative pyrolysis (= combustion) . This differentiation is implicit in paragraph F4 , but no where

in the outline is it explicit.

Such a differentiation raises the question: How accurate

is our knowledge about rate constants resulting in a closed

system , completely free of any trace of 02 , H20 , or any other oxygenated compound ? The knowledge of non-oxidative

pyrolysis is necessary to study efficiently the oxidative

pyrolysis (= combustion)

.

7-26 Topic: CH4 Pyrolysis and Oxidation; use of Post Shock Front Density Gradient Technique.

S . H . Bauer , Cornell University . Following my brief description of the early stages of the methane pyrolysis

and oxidation (fuel-rich regime):

1) Professor F . Kaufman excitedly pointed to one of my slides which showed:

CH4 + OH -> CH3 + H20 k = 3.00 x 10 13 exp (-60 , 000/RT) This is clearly a typographical error, for which I apologize. The value we used in our model was: 3.00 x 10 13 exp(-6, 000/RT) , based on the work of Peeters and Mahnen, 14th Combustion Symposium.

66
2) Professor A. M. Dean questioned our use of the reaction: CH20 + M = CO + H2 + M k = 2.10 x 10 16 exp (-35 , 000/RT)

This was also taken from Peeters and Mahnen's paper. Indeed, in our complete analysis we tested the alternate

route for the decomposition of formaldehyde:

CH20 + M -> CHO + H + M CHO + M -> CO + H + M CHO + 02 -> CO + H02 CHO + H -> CO + H2 When we inserted a suitable set of rate constants for these

steps, essentially in agreement with the work of Schecker

and Jost, which Dean favors, we found that all the computed

density gradient profiles were essentially

indistinguishable from those based on the single direct

decomposition step. In other words, our experiments cannot discriminate between these two mechanisms.

In my brief description of the use of the psfdg technique I attempted to show its utility as a diagnostic for detailed

studies of induction periods prior to the onset of ignition. I am not aware of any other experiments which

provide this type of information. However, I should also

add, that the conclusions derived from the density gradient

profiles are limited (as is any other single diagnostic)

.

We can make statements only with respect to reactions which

either directly or indirectly (through the production of reactive intermediates) affect the thermal balance in the shock heated sample. Thus, on the basis of our data alone, we could derive no information on the role of CH2 in the CH4 pyrolysis, nor the detailed path for the decomposition

of CH20. On the other hand, the need for the highly

exothermic step: CH3 + 02 -> CH20 + OH

is loud and clear for T>2000 K. We underscore the need to couple several types of diagnostics for providing sharper

criteria for reaction mechanisms.

67
7-27 Topic: High Density Kinetics.

J. C. Keck , Massachusetts Institute of Technology . In the investigation of individual reaction rates related to combustion, it is very important to include measurements at high densities, 1 to 100 atmospheres. This is the range in which the order of many of the rate controlling reactions may be expected to change from trimolecular to unimolecular

in character and the assumption of bimolecular scaling is highly questionable.

Topic: Relation Between Combustion of Benzene et al . to Coal

A. L. Myerson , Exxon . It would certainly seem that we are

all basically in agreement concerning the serious need for chemical kinetic data on the combustion and pyrolysis of aromatics and other coal-relevant molecules. One technique

which seems to possess considerable advantage for such research is the single-pulse shock tube. This leads to a major point' in our long-range research

needs. If we are to expend considerable effort on the study of these coal-relevant molecules, a major effort will have to be made on correlating the behavior of these more tractable molecules with that of coal itself. This means

that many of us will have to make side-by-side or parallel

studies of coal and coal-relevant molecules under as relatable conditions as feasible.

Topic: Applicability of Various Kinetic Techniques.

C. B S kinner , Wr ight State University . It seems useful to make a concise list of some of the principal techniques in kinetics, with their typical applications. Seven techniques are listed below without meaning to imply that there are no others.

7-28

7-29

Technique Application

.1

.

Molecular beams. Elementary reactions, often with state selection.

2. Low-pressure flow reactors

.

Often useful for elementary

reactions - sometimes with

compl ications

.

68
3. Static reactors. Same as 2. Mainly used recently for unimolecular

reactions

.

4. Photochemistry. Used to produce active species

or study reactions of highly

energized molecules.

5. Shock tubes. Elementary reactions in favorable cases - more often

for study of groups of reactions.

A good point to model the kinetic subsystem of a complex combustion

reaction

.

6. High Pressure Flow Usually involves groups of Reactors. reactions. Transport properties

often of considerable importance.

7. Laminar flames. Same as 6 - Transport properties

always important, but not very

hard to handle.

The methods are listed in decreasing order of the simplicity of understanding the final results (but not of carrying out the experiment). All are valuable in providing data of different types to use in combustion

studies

.

7-30 Topic: Role of Shock Tubes in Kinetics Research.

G. B. Skinner , Wr ight State University . Single elementary

reactions may be studied in a shock tube under favorable circumstances. Perhaps even more important for combustion

research, this technique can be used to study the net effect of groups of reactions (such as in hydrocarbon

oxidation) under temperature and pressure conditions

commonly reached in practical combustion processes, with

minimal influences of heat and mass transfer effects and minimum wall catalytic effects. For modelers, simulation

of shock tube data provides an opportunity to check out a complete kinetics sub-system before combining it with transport property sub-systems. Under some conditions, the shock tube can also be used to study wall quenching of reactions under conditions close to those in practical

combustion systems.

69
7-31 Topics Monitoring Radical Concentrations.

D. Bogan , Naval Research Laboratory . Development of laser assisted optical diagnostic techniques is receiving

considerable attention. When these methods are (become)

available for a particular species they are (will be) the methods of choice because they cause the minimum

perturbation in complex chemical systems. Nevertheless,

the beam sampling differentially pumped mass spectrometer

is probably still the most generally useful diagnostic tool

for gas phase kinetics. The most serious problem of the mass spec, i.e. extensive ion fragmentation, can be overcome by using photo ionization

.

High power lasers in the UV and near UV have recently

become widely available. These offer the possibility of combining laser multiphoton ionization with the mass spec. Most free radicals have low lying electronically excited

states and will absorb at longer wavelength than stable species which are simultaneously present in kinetic

studies. Hence sensitive detection of free radicals should

be obtainable with species selectivity in both the wavelength of the multiphoton process and in the mass to charge ratio of the ionized species.

7-32 Topic? 1) Needs for High Temperature Kinetics Data.

2) Acquisition of High Temperature Kinetic Data.

D. J. Seery , United Technologies Resear ch Center . 1) One clear consensus, that seemed evident to me, was, the need for high temperature chemical kinetics studies of fuel-rich hydrocarbon oxidation. These studies of reactions such as R. + R! and R. 4- R ' H should include both aromatic and aliphatic species.

2) The one experimental technique capable of measuring

both stable and unstable species at high temperatures is molecular beam sampling - mass spectrometry. Considering

the potential of this technique for studying reactive

systems, it is disappointing that so few research labs are pursuing this path.

70
7-33 Topic: Dye laser intracavity absorption and enhancement.

G. 0. Brink , SUNY-Buf f alo « The possibility of the use of tunable dye laser" intracavity absorption or enhancement as

a diagnostic tool in combustion research should not be overlooked in the design of kinetic experiments or in the planning of the new laser diagnostic facility. We have been examining the application of this technique to the detection of atomic sodium in an atomic beam, and have detected as few as 10 6 atoms in absorption and less than

10^ in enhancement.

At the present time the intracavity process is not understood and additional work will be required before it could be used as a routine diagnostic. However, the high

sensitivity and good spectral fidelity that may be obtained make the technique potentially valuable for combustion

research

.

7-34 Topic: Radical Generation by C02-TEA Laser Photolysis

R. Huie , National Bureau of Standards . Recently, J. T. Herron, W. Braun, W. Tsang and I have been working on a new method for the generation of high concentration of free radicals in a controlled manner: infrared laser photolysis. Specifically, we have used a C02-TEA laser to produce CF2 from the photolysis of CF2HC1. The reaction

CF2 + CF2 + M -> C2F4 + M was monitored using a guadrupole mass spectrometer and a rate constant derived which is in excellent agreement with the literature value. From the amount of C2F4 produced, we estimated that 140 mtorr of CF2 was produced using laser fluence of 8 J cm-2. Not only do we feel that this method will be of great

utility for the study of reactions of a large number of radicals near room temperature, we envision that the technique may allow the generation of non-equilibrium

concentrations of selected radicals in flames, where their influence on flame chemistry may then be determined.

71
7-35 Topic: New Experimental Techniques.

A. Fonti jn , AeroChem Research Labs . The need for elementary reaction kinetic data of realistic temperatures

and wide temperature ranges has been implicitly emphasized

frequently in this meeting. Dr. Garvin this morning

mentioned our HTFFR (high-temperature fast-flow reactor)

technique in which we have studied metal atom oxidation

kinetics at temperatures from 300 to 1900K and pressures

from 3-150 Torr. As in many hydrocarbon combustion

reactions Arrhenius behavior is often not obeyed in these processes.

Under such conditions extrapolations over wide temperature

ranges are not meaningful; in the A1/C02 reaction

extrapolation of the 300-700K data to 1900 K would have given a rate coefficient an order of magnitude too low

(J. Chem. Phys. 67/ 1561 (1977)). The HTFFR as such appears unsuited for similar hydrocarbon

combustion reaction studies because of pyrolysis problems.

However, with support from DOE, Dr. Felder and I have now adapted another previously essentially low temperature

technique, pulsed photolysis resonance fluorescence/

absorption, to be useful for the same wide temperature

range. With such an HTP (high temperature photolysis) reactor we have now initiated study of the 0/CH4 reaction,

to be followed by OH or 0 with C6H6 and 0/CH3. The range of pressures which can be covered with the HTP is probably

even larger than indicated above for the HTFFR; 3-760 Torr

is anticipated. We suggest that once our initial studies have demonstrated the practicality of the HTP technique, it should be widely applied.

72
7-36 Topic: Kinetic Sensitivity Testing - A Quantitative Basis.

R. J . Gelinas , Science Applications . A recurrent phrase in this meeting has been, "What is important (chemically)?" In partial answer, I will briefly indicate an increasingly

quantitative basis for importance assessments that is currently under development.

Three general axioms are well-advised in testing the importance of individual chemical reactions in flames; they are:

1. Emphasize elementary physical and chemical processes to the greatest practical extent.

2. Retention or rejection of elementary reactions is very

much a problem-specific matter, in which physical and chemical mechanisms play off, relatively, against each

other

3. Resist the urge to reject candidate processes

prematurely.

Each of these axioms is worthy of discussion at another

time. To test kinetics mechanisms two quantitative levels

of analysis are important:

.Purely kinetics sensitivity analysis

•Coupled kinetics-fluid dynamics sensitivity analysis. Both are essential to validating a kinetics mechanism for specific applications.

The governing equations for chemical species densities,

y i (x,t) (particles cm-3) , are: yi(x,t) = E|p"(y) - ^(yjy.j +TA

, i=l,N where Pj and L^y^ are rate expressions (of the form k a y

k a y^, etc.) for individual reaction processes which produce

and destroy the ith chemical species at (x,t); and T^ is the local rate of transport of the ith chemical species at

(x,t)

PURELY KINETICS ANALYSIS

In purely kinetics analysis T^ is neglected. Two quantitative stages of importance testing can be exercised.

The first simply rank-orders all the individual reaction

terms P°(y) and L*{y)y i which constitute the y^'s at all interesting problem times. Reaction rank-ordering can also

be extended to energy conservation equations. It is generally found that reactions shift about in rank-ordering

as time evolves. Reactions that are not important over short time scales may become important over longer time

73
scales, etc. Examples are contained in references 1 and 2. The second quantitative stage evaluates sensitivity

variables, <^y^ , dk , which are a measure of the resultant variation in the solutions, y i (x , t) , with respect to intrinsic variations (uncertainties) in the rate parameters. The time-honored method of evaluation dy/^k

introduces an arbitrary variation, Ak , into a given rate parameter, k, and solves the perturbed kinetic mechanism.

The sensitivity is obtained from the difference quantity

[y (k+Ak ,t) - y(k,t)]/Ak. Several new computational methods

(3-7) are now appearing which attempt to evaluate dy/dk

without repeated solutions of the kinetics mechanism. The new methods all have economical or logical problems, which

have impeded widespread practical applications to the present time. Further research should resolve many of these problems. COUPLED KINETICS-FLUID DYNAMICS ANALYSIS

For coupled analysis the magnitudes of the transport rates,

T^ (x,t) , may be highly variable from one point to another

in space and in time for flame systems. The transport

rates, of course, depend upon gradients which are driven by the energy and momentum equations, coupled to the chemical

species. Depending upon local, problem-specific

conditions, fluid dynamics coupling can markedly alter the sensitivity results that would be obtained from a purely

kinetics analysis. Reaction rank-ordering vis a vis, Ti

,

can be readily accomplished in 1-D and 2-D transient

analysis operating on both species and energy equations, as

a function of space and time. Only the time-honored method

is currently practical for evaluating sensitivity

variables, dy^/dk, in 1-D or 2-D transient systems. REFERENCES

1. Gelinas, R.J., "Methane Combustion Kinetics", SAI Report

No, SAI/PL-NI-77-02 (October 18, 1977).

2. Gelinas, R.J. and Skewes-Cox, P.D. "Tropospher ic Photochemical Mechanisms", Symposium on Reaction

Mechanisms, Models, and Computers, American Chemical

Society 173rd National Meeting, New Orleans, LA, (March

20-25, 1977). J. Phys. Chem. 81, 2468 (1977).

3. R. I. Cukier, CM. Fortuin, K. E. Schuler, A. G. Petsche

and J. H. Schaibly, J. Chem. Phys. 59 , 3873, (1973).

4. J. H. Schaibly and K. E. Schuler, J. Chem. Phys. 59 , 3879, (1973).

5. R. W. Atherton, R. B. Schainker , and E. R. Ducot , AIChE

(March 1975) . 6. Dickinson, R. P. and Gelinas, R. J., "Sensitivity Analys

of Ordinary Differential Equation Systems ", J

.

Computational Physics , 21, No. 2, 123-143, (June 1976).

7. Stolarski, R. , NASA Goddard Reports X-624-77-122 and 123

(1977) (on Stochastic Sensitivity Methods)

.

74
7-37 Topic: Acquisition and Needs for Kinetic Data

W. Tsang , National Bureau of Standards . Single Pulse Shock

tube experiments can be an excellent means of determining

the mechanisms and rates of initiation in pyrolytic and many oxidative hydrocarbon decomposition systems. This is because the short reaction times < 1 msec and the low dilutions at which experiments are carried out (due to the sensitivity of gas chromatographic detectors) prevent all except the initial unimolecular decomposition processes

from occurring. These same conditions permit the use of an internal standard, [a unimolecular decomposition whose rate parameters are well established] thus guaranteeing data of the highest precision and accuracy. It should be noted that these measurements are particularly suited for the derivation of correlations in rate parameters since these Quantities are always compared with one another. At present sufficient data have been accumulated so as to permit derivation of the rate parameters for the initiating process (bond-breaking) in the decomposition of practically

all aliphatic hydrocarbons.

With this information as a base, and with suitable

adjustment of reactant concentrations measurements on the rates of many of the chain processes can and are presently

being carried out. These include H and CH3 radical attack on aliphatic and unsaturates as well as branching ratios

for the decomposition of alkyl radicals. It appears that

the complete set of rate constants for the decomposition of aliphatic hydrocarbons to small unsaturates such as ethylene or acetylene are accessible. This in turn will

set the stage for decomposition studies in the presence of increasing quantities of oxygen. The analogy here is with

the work of Baldwin and coworkers where complete

understanding of the H2, 02 system permit studies on the effect of added hydrocarbons.

The strategy outlined above can be easily applied to studies on aromatic and heterocyclic systems. The one fundamental problem is that of analysis. Specifically, can trace quantities of such compounds and related products be reproducibly introduced and withdrawn from a single pulse

shock tube? The most obvious solution is to maintain the shock tube at several hundred degrees C. We do not believe

that there are any intrinsic problems. Furthermore in view

of the need for the data as outlined by Drs. Dryer and Glassman and that the same apparatus may be of use for determining the mechanism of soot- formation (through

analysis of the "pr e-soot"compounds that may be formed)

75
experiments of this type would certainly appear to be worthwhile.

Finally, we note that in a more general sense the important advances in instrumentation in recent years are such that measurements can be made at increasingly shorter times, lower concentrations and on more exotic or unstable

species. Thus virtually all reactions involving thermally

equilibrated ground state molecules are accessible. The single pulse shock tube measurements mentioned above are a reflection of these advances. The main need is for careful systematic work with emphasis on the elementary processes.

76
7-38 Topic: Reactions of OH and HO2

S. Gordon , Argonne National Laboratory . It is clear that combustion using coal and oil as well

as new fuels used in conventional and new combustion

techniques is of increasing importance. Knowledge of the combustion process is therefore important in increasing the efficiency of these techniques and in designing new combustion concepts. It is well known that combustion

results from a chain process involving OH and H02 radicals

which are initially produced by thermal process at rather

high temperatures. The condition for ignition in the burning of fuels are such that very complex reactions

involving competing, sequential, and chain branching

reactions, occur in which the OH and H02 radicals play a role

.

We have the capability of studying the individual elementary reactions of these radicals under controlled

experimental conditions. To date we have determined rate constants for the reactions of the OH radical with a large number of simple hydrocarbons including saturated,

olefinic, and aromatic compounds as well as a number of simple inorganic compounds such as NH3, N20, NO, N02, S02, and C02. These studies were carried out at temperatures

ranging from 300 to 440 K and at total pressures of reactant plus inert gas of about 1 atmosphere. We are extending our work to 600-700 K. In addition we have studied the rate constants for the following reaction:

H02 + H02 -> H202 + 02.

(k = 1.9 x 10 9 M-l sec-1 in absence of H20, Hamilton, J. Chem. Phys. 6_3 , 3682 (1975).

Knowledge of the reaction rate constants for this process is vital to the understanding of combustion and atmospheric reactions involving H02. Many rate constants

have been determined for H02 reactions in competition with

the above recombination reaction. There has been a great

variation in the literature on the above rate constants.

We have shown that the reported discrepancies can be explained by the presence of water vapor, since the H02 and water form a relatively stable complex which influences the rate of recombination of the H02 radicals. We have found

that NH3 has even a greater effect on this reaction. Our studies indicate that as much as 35% of atmospheric H02

77
could be complexed at relatively high humidities. Another important reaction is the cross reaction between OH and

H02. There is presently an approximately 30-fold uncertainty in the rate constant for this reaction. With

our 2 MeV Febetron and associated gas phase-pulse

radiolysis apparatus, we have completed the experimental

portion of the work on this reaction. H20-02-Ar (or N2) mixtures at one atmosphere were pulse radiolyzed. The decays of OH (309 nm) and H02 (230 nm) were followed as a function of reactant concentration, dose, dose rate, total pressure and diluent gas. Our work will eliminate or sub- stantially reduce the uncertainty in the rate constant

resulting from the previously reported studies. Research

has also been initiated on the reaction of H02 with S02. We are also extending our program to determine the reactivity of OH and H02 with organic compounds to determine the products of these reactions. [Comment

abridged, tables of rate constants omitted, Ed.]

78
Author Index to Comments

Bauer , S . H

.

7—21 j 7-26 Bogan, D. 7-31 Bowman, C. T. 7-9

Br ink , G . 0

.

7—33 Dean , A . M

.

7—6 Dorko, E. A. 7-14 Edelson, D. 7-2 Engleman, V. 7-3 Fontijn, A. 7-7 , 7-8, 7-35 Gann, R. G. 7-16

Gel inas , R. J

.

7-15 7-23, 7-36 Gordon, S. 7-38 Huie, R. 7-34

Indr i tz , D

.

7-24 Keck , J . C

.

7-4

,

7-27

Kwe i , G . H

.

7-17 7-18 Lauf er , A

.

7-12

Lin, M. C. 7-13 McLean, W. J. 7-10 Myerson, A. L. 7-5

,

Til -i "700 7-11, 7-22, 7-28 Seery, D. J. 7-32

Shaw, R. 7-19 Skinner, G. 7-20 7-29, 7-30 Tsang, W. 7-37 Westbrook, C. 7-1 Westley, F. 7-25

79
8. List of Registrants

Stanley Abramowitz

National Bureau of Standards

Building 222, Room B350 Washington, DC 20234

0. William Adams Department of Energy

Div. Basic Energy Sciences

Washington, DC 20545 David L. Allara

Bell Laboratories

7F-212 Murray Hill, NJ 07974 Pierre Ausloos

National Bureau of Standards

Bldg. 222, Room A243 Washington, DC 20234 Donald L. Ball AFOSR/NC

Boiling AFB Washington, DC 20332

A. M. Bass National Eureau of Standards

Bldg. 222, Room B162 Washington, DC 20234

E . Karl Bastrass Department of Energy

20 Massachusetts Ave., NW Washington, DC 20545

S. H . Bauer Cornell University

Department of Chemistry

Ithaca, NY 14853 Sidney W. Benson Department of Chemistry

Univ. of Southern California

Los Angeles, CA 90009

Joan C. Biordi

U.S. Bureau of Mines

c/o David Forshey

2401 E Street, NW Washington, DC 20241

J. W. Birkeland

Department of Energy

20 Massachusetts Ave., NW Washington, DC 20545 Denis J. Bogan Naval Research Lab. Code 6180 Washington, DC 20375 Craig T. Bowman

Mech. Eng. Dept. Stanford University

Stanford, CA 94305

C. 0. Brink

Dept. Physics & Astronomy

Fronczak Hall SUNY - Buffalo

Amherst, NY 14250 Robert L. Brown National Bureau of Standard

Bldg. 222, Room B152 Washington, DC 20234 Julius S. Chang Lawrence Livermore Lab

P.O. Box 808 Livermore, CA 94550 Norm Cohen Aerospace Corporation

Building 130, Boom 150 P.O. Box 92957

Los Angeles, CA 90009

80
Anthony M . Dean

Univ. Missouri - Columbia

Chemistry Department

Columbia, MO 65201 Ernest A. Dorko

AF Inst, of Technology

Attn: AFIT/ENY

Wright-Patterson AFB, OH 45433 Frederick L. Dryer

Princeton University

Room D-315A, Engr. Quad.

Princeton, NJ 08540

David Edelson

Bell Laboratories

600 Mountain Avenue

Murray Hill, NJ 07974 Victor S. Engleman

Science Applications, Inc. 1200 Prospect Street

La Jolla, CA 92037 Richard C. Farmer

Dept. of Chem. Engr.

Louisiana State University

Baton Rouge, LA 70803 William Felder

! AeroChem Research Labs.

P.O. Box 12 Princeton, NJ 08540

Paul R. Fields

Argonne National Laboratory

Chemistry Division

9700 S. Cass Avenue

Argonne, IL 60439

[A. Fontijn AeroChem Research Lab., Inc.

P.O. Box 12 Princeton, NJ 08540

Robert M. Fristrom

Johns Hopkins University

Johns Hopkins Road Laurel, MD 20810

Richard G. Gann National Bureau of Standards

Bldg. 225, Room B06 Washington, DC 20234

W. C. Gardiner

Univ. of Texas WEL 103W Austin, TX 78712

David Garvin

National Bureau of Standards

Bldg. 222, Room B346 Washington, DC 20234 Robert J. Gelinas

Science Applications, Inc.

80 Mission Drive Pleasanton, CA 94566 Lewis H. Gevantman

National Bureau of Standards

Bldg. 101, Room A529 Washington, DC 20234

I. Glassman

Princeton University

Princeton, NJ 08540 David M. Golden

SRI International

333 Ravenswood Avenue Menlo Park, CA 94025 Robert Goulard George Washington Univ. SEAS-CMEE Washington, DC 20052 David Gutman

Illinois Institute of Technology

Department of Chemistry

3300 S. Federal St. Chicago, IL 60616 Joshua Halpern

Howard University

Department of Chemistry

Washington, DC 20059

81
Robert F. Hampson, Jr. National Bureau of Standards

Bldg. 222, Room A165 Washington, DC 20234 Ronald K. Hanson

Stanford University

Mechanical Engineering

Stanford, CA 94305

Don Hardesty

Sandia Labs Livermore, CA 94550

Charles E. Hunter Hampton Inst. /Ford Motor Co. Hampton, VA 23668 Robert E. Huie National Bureau of Standards

Bldg. 222, Room A145 Washington, DC 20234 Doren Indritz Princeton University

Frick Chemistry Lab Princeton, NJ 08540

Dan L. Hartley

Department 8350 Sandia Laboratories

Livermore, CA 94550 John W. Hastie

National Bureau of Standards

Bldg. 223, Room A307 Washington, DC 20234 Edward F. Hayes

National Science Foundation

Chemistry Division

Washington, DC 20550

J. Herron National Bureau of Standards

Bldg. 222, Room A145 Washington, DC 20234 Jimmie Hodgeson

National Bureau of Standards

Bldg. 222, Room A345 Washington, DC 20234

E. Horowitz

National Bureau of Standards

Bldg. 223, Room B362 Washington, DC 20234 Jeffrey W. Hudgens

Naval Research Lab Code 6110 Washington, DC 20375 Jerome Hudis Brookhaven National Lab. Chemistry Department

Upton, NY 11973

Marilyn E. Jacox National Bureau of Standards

Bldg. 222, Room A243 Washington, DC 20234 Richard J. Kandel Department of Energy

Division of Basic Energy Sciences Washington, DC 20545 James S. Kane Department of Energy

20 Massachusetts Ave., NW Washington, DC 20545 Takashi Kashiwagi

National Bureau of Standards

Bldg. 225, Room A07 Washington, DC 20234 Frederick Kaufman Department of Chemistry

University of Pittsburgh

Pittsburgh, PA 15260 James C. Keck Massachusetts Inst, of Tech. Room 3-342 Cambridge, MA 02139 George E. Keller

US Army Ballistic Research Lab Aberdeen Proving Ground, MD 210

R. D. Kern Department of Chemistry

University of New Orleans

New Orleans, LA 70122

82
John H. Kiefer

Univ. of Illinois, Chicago

Chicago, IL 60680 Nathan Klein Ballistic Research Lab Aberdeen Proving Ground, MD 21005

R. Bruce Klemm Brookhaven National Lab

Bldg. 527 Upton, NY 11973 Walter Koski Department of Chemistry

Johns Hopkins University

Charles and 34th Streets Baltimore, MD 21218 Michael J. Kurylo

National Eureau of Standards

Bldg. 222, Room A145 Washington, DC 20034 George H. Kwei

Los Alamos Sci. Lab.

MS 732, Los Alamos Sci. Lab. Los Alamos, NM 87545 Allan H. Laufer National Bureau of Standards

Bldg. 222, Room A145 Washington, DC 20234

Yuan T. Lee Lawrence Berkeley Lab. Bldg. 70A, Room 4414

Univ. of California

Berkeley, CA 94720 Robert S. Levine

National Bureau of Standards

Bldg. 225, Room B64 Washington, DC 20234 Arthur Levy Battelle Columbus Lab.

505 King Avenue

Columbus, OH 43201

M . C. Lin Naval Research Lab. Washington, DC 20375 Ralph Livingston

Oak Ridge National Lab

P.O. Box X Oak Ridge, TN 37830 Andrej Macek Department of Energy

20 Massachusetts Ave., NW Washington, DC 20545 William G. Mallard National Bureau of Standards

Bldg. 225, Room B06 Washington, DC 20234 Michael J. Manka National Bureau of Standards

Bldg. 225, Room B06 Washington, DC 20234

R. A. Marcus University of Illinois

174 Noyes Laboratory

Urbana, IL 61801 Richard I. Martinez

National Bureau of Standards

Bldg. 222, Room A243 . Washington, DC 20234 Joseph. F. Masi

AF Office of Sci. Res. Building 410 Boiling Air Force Base Washington, DC 20332 Max S. Matheson

Argonne National Lab 9700 South Cass Avenue Argonne, IL 60439 William J. McLean Cornell University

284 Grumman Hall Ithaca, NY 14853

83
Albert L. Myerson

Exxon Res. & Engr. Company

P.O. Box 8 Linden, NJ 07036 Cheuk-Yiu Ng Ames Laboratory

Metallurgy Room 106 Iowa State University

Ames, IA 50011 Robert C. Oliver

Inst, for Defense Analyses

400 Army-Navy Drive Arlington, VA 22202 Elaine Oran

Naval Research Laboratory

Code 7750 Washington, DC 20375 Howard B. Palmer Penn State University

319 M . I. Bldg.

University Park, PA 16802 Elliot S. Pierce

Div. of Basic Energy Sciences

Department of Energy

Washington, DC 20545 Herschel Rabitz

Department of Chemistry

Princeton University

Princeton, NJ 08540

R. F. Sawyer

Dept. Mechanical Engr.

University of California

Berkeley, CA 94720

Daniel J. Seery

United Tech. Res. Cntr. Silver Lane East Hartford, CT 06108 Robert Shaw Lockheed Missiles & Space Co. 3251 Hanover Street

Palo Alto, CA 94304 David M. Silver Johns Hopkins University

Applied Physics Laboratory

Johns Hopkins Road Laurel, MD 20810 Walter Shaub

Naval Research Laboratory

Washington, DC 20375 Gordon B. Skinner Wright State University

Department of Chemistry

Dayton, OH 45435 Michael W. Slack Grumman Aerospace

Research Department, Pit. 5 Bethpage, NY 11714 William S. Smith

Federal Aviation Agency

800 Independence Ave., SW Washington, DC 20591 Kermit C. Smyth

National Bureau of Standards

Bldg. 225, Room B06 Washington, Dc 20234

8H
William Spindel

National Academy of Sciences

National Research Council

2101 Constitution Ave., NW

Washington, DC 20418

David R. Squire

US Army Research Office

P.O. Box 12211 Research Triangle Park, NC 27709

F. Dee Stevenson

Department of Energy

Div. Basic Energy Sciences

Washington, DC 20545

Wing Tsang

National Bureau of Standards

Bldg. 222, Room A145 Washington, DC 20234 Albert F. Wagner

Argonne National Laboratory

Chemistry Division

9700 S. Cass Avenue

Argonne, IL 60439

James A. Walker National Bureau of Standards

Bldg. 222, Room A145 Washington, DC 20234

Karl Westberg

The Aerospace Corporation

P.O. Box 92957

Los Angeles, CA 90274 Charles K. Westbrook

Lawrence Livermore Laboratory

P.O. Box 808 L-71 Livermore, CA 94550 Francis Westley

National Bureau of Standards

Bldg. 222, Room A145 Washington, DC 20234 Bernard T. Wolfson

AFOSR Aerospace Sciences Directorate

Boiling Air Force Base Washington, DC 20234

85
HBS-1I4A (REV. 5-78)

J.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

4. TITLE AND SUBTITLE

1. PUBLICATION OR REPORT NO. NBS SP-531

Summary Report on the Workshop on High Temperature Chemical Kinetics: Applications to Combustion Research

3. Recipient's AC c<

5. Publication Date December 1978

6. Performing Organiz

7. AUTHOR(S)

D. Garvin, R. L. Brown, R. F. Hampson, M. J . Kury to

f W. Tsang

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C 20234

:t/Task/Work Unit No.

11. Contract/Grant No. E A- 77 -A -01 -06 10

12. Sponsoring Orgar mplete Addre > (Sir H, City, State, ZIP) Department of Energy, Washington, D.C. 20545 and Office of Standard Reference Data, National Pureau of Standards, Washington, D.C. 20234

14. Sponsoring Agency Code

IS. SUPPLEMENTARY NOTES Library of Congress Catalog Card Number 78-600125

16. ABSTRACT (A 200-word or less factual summary ot most significant information. If document includes a significant bibliography or literature survey, mention it here.) The proceedings at a workshop on the applications of high temperature chemical kinetics to combustion research are summarized. This workshop, held Dec. 12-13, 1977 at the National Bureau of Standards, provided a forum for the exchange of views on

the needs for kinetics research during the next five to ten years. Experimental techniques, measurements, theoretical developments and data evaluation were treated

in four review papers and two discussion sessions.

This report contains the program of the meeting, abstracts of the review papers,

a commentary by the organizers of the meeting, summaries of the discussions, formal comments submitted by the participants and an attendance list.

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