Workshop on Combustion Simulation 

Databases for Real Transportation Fuels

Viable Operating Range Predictions ‡

1

2

3

4

5

6

7

0 10 20 30 40 50 60

EGR (% by mass)

Lambda

calculation

point

93%

Knock limit (β = 1)

Misfire (93% burned)

Expt. limit (Oakley et al.)

92%

94%

β=1

0.5

2

Viable Operating Range Predictions ‡

1

2

3

4

5

6

7

0 10 20 30 40 50 60

EGR (% by mass)

Lambda

calculation

point

93%

Knock limit (β = 1)

Misfire (93% burned)

Expt. limit (Oakley et al.)

92%

94%

β=1

0.5

2

September 4-5, 2003 

National Institute of Standards and Technology 

Gaithersburg, Maryland

NISTIR 7155 
 ii

Cover Page Figures: 

• Upper left: Civilian aircraft flying over a city. 

• Upper right: Night time view of a refinery that produces transportation fuels. 

• Lower Left: Potential energy surface for addition of phenyl radical to acetylene, showing some 

isomerization reactions and product channels. Adapted from H. Richter, MIT. 

• Lower right: Graph plotting the predicted and experimental knock and misfire limits for a homogeneous 

charge compression ignition (HCCI) test engine. Adapted from W. Green and P. Yelvington, MIT.
 iii

Workshop on Combustion Simulation Databases for Real 

Transportation Fuels 

Report of the workshop conducted at the National Institute of Standards and Technology, 

Gaithersburg, MD, September 4-5, 2003 

Sponsored by the Physical and Chemical Properties Division, Chemical Science and Technology 

Laboratory, National Institute of Standards and Technology, Department of Commerce 

Organizing Chair 

Wing Tsang 

Editor 

Jeffrey W. Hudgens 

Report Writing Team 

Thomas C. Allison 

Donald R. Burgess, Jr. 

Jeffrey W. Hudgens 

Jeffrey A. Manion 

David M. Matheu 

Wing Tsang 

 NISTIR 7155
 iv
 v

TABLE OF CONTENTS 

Executive Summary ....................................................................................................... vii

Workshop Report

I. Introduction ................................................................................................... 1

II. Session Presentations ................................................................................... 4

A. Physical and Chemical Property Data

1. Overview ......................................................................................... 5 

2. Individual Talks .............................................................................. 6 

i. John Farrell 

ii. Daniel Friend 

iii. M.C. Lin 

iv. Wing Tsang 

B. Fuels and Surrogates 

1. Overview ........................................................................................ 9

2. Individual Talks .............................................................................. 11 

i. William L. Brown 

ii. Meredith B. Colket 

iii. Tim Edwards 

iv. David Lenhert 

v. Adel Sarofim 

vi. Mitchell D. Smooke 

C. Simulations and Kinetics

1. Overview ........................................................................................ 13

2. Individual Talks .............................................................................. 14

i. C. Thomas Avedisian 

ii. Anthony M. Dean 

iii. Frederick L. Dryer 

iv. Graham Goldin 

v. Viswanath Katta 

vi. Chung K. Law 

vii. Gregory J. McRae 

viii. William J. Pitz 

ix. Charles K. Westbrook 

D. Community Collaboration 

1. Overview ........................................................................................ 19

2. Individual Talks .............................................................................. 19

i. Michael Frenklach 

ii. David M. Golden 

iii. William H. Green 

iv. Larry Rahn 

III. Breakout Session Reports .......................................................................... 21

A. Reference Fuels .................................................................................... 21 

B. Surrogate Fuel Selection ..................................................................... 24 

C. Essential Databases ............................................................................. 27 

D. Experimental Validation Data Sets ................................................... 29 

E. Creation of a Roadmap for Combustion Science ............................. 30 

Glossary............................................................................................................................ 32

Sponsorship ...................................................................................................................... 34

List of Attendees ............................................................................................................. 35
 vi
 vii

EXECUTIVE SUMMARY

Overview

A workshop entitled "Workshop on Combustion Simulation Databases for Real Transportation 

Fuels" was held on September 4-5, 2003 at the National Institute of Standards and Technology 

(NIST) in Gaithersburg, MD. The workshop was organized in response to the recognized 

overwhelming importance of energy to the United States economy, the increasing need to 

optimize combustion processes for efficiency and pollution minimization, and to address the 

increasing role of computer simulations in all areas of design. Approximately sixty scientists and 

engineers from industry, academia, and government (civilian and military) attended the 

workshop. 

The economic, environmental, and health benefits accruing to the nation from improved 

combustion processes for transportation are enormous and well-recognized. Technologicallyfeasible advanced engine technologies would operate more efficiently, saving the nation at least 

$50B/year in fuel costs, and reducing substantially the global warming load associated with CO2

production. Health and environmental benefits estimated at ~ $62B/year would accrue through 

reductions of health problems (e.g., pollution-induced asthma and heart disease), crop damage, 

and visibility enhancements, due to the lower chemical and particulate emissions from advanced 

engines. 

For these benefits to be realized, it is necessary to efficiently translate our underlying scientific 

understanding to technological development. Future engines will require stringent control of the 

combustion environment, which is determined by complex interactions of the combustion 

chamber with the chemical composition, physical properties, and combustion properties of fuel. 

The overall aim of the present workshop was to create a forum that would help NIST and the 

combustion community to assess the data needs of studies involving transportation fuels and to 

recommend plans for developing reference databases and chemical kinetic models. These 

databases and models will enable the combined application of chemical kinetics and 

computational fluid dynamics (CFD) programs to simulate combustion processes realistically. 

The target applications were envisioned to be real liquid transportation fuels, which we refer to 

hereafter as "real fuels," and include aviation, diesel, and gasoline fuels. 

Some specific objectives were 1) to evaluate the benefits and feasibility of a cooperative program 

that focuses upon the combustion of real fuels; 2) to evaluate the benefits and feasibility of using 

surrogate mixtures and modeling thereof to realistically describe the important characteristics 

and behavior of real fuels; 3) to broadly assess the data needs; 4) to assess the community's 

willingness to work together to address the data and information needs for model-based design 

and; 5) to assess how to make better use of knowledge management structures to facilitate 

information exchange and more rapid progression from the laboratory to applications. 

The following section outlines the findings of the Workshop as perceived by NIST. 
 viii

Workshop Findings

In broad terms the outcomes may be grouped as those related to the existence and quality of 

relevant data and models (items 1-5) and those related to the need for a better infrastructure for 

sharing, analyzing, and comparing data and models (items 6-8). 

1) Computational simulations incorporating realistic fluid dynamics and chemistry are 

poised to be of great benefit in the design of real combustion devices (e.g., internal 

combustion engines) that are vital to the nation's energy and environmental goals. This 

new simulation capability may also accelerate the development of novel energy 

technologies, e.g., hydrocarbon reforming for hydrogen fuel production. 

2) The dearth of critically evaluated thermochemical, kinetic, and transport data severely 

hampers the development of predictive chemical models and simulations for combustion 

as well as other technologies. The published literature contains a proliferation of 

chemical kinetic models for combustion at different conditions. Although they may fit a 

set of results, they are a reflection of the science at that time; hence, they may now be 

incorrect, inconsistent, or in conflict with other established models and are definitely not 

extensible. 

 

i. Much of the thermochemical, thermophysical, and reaction rate data used in 

chemical kinetic modeling has not been compared to evaluated data, nor 

systematically checked for self-consistency. 

ii. There is no generally-accepted set of results on experimental systems that can be 

used to inter-compare and refine chemical kinetic models. 

iii. Essentially no generic software tools are available for comparison and evaluation 

of combustion models. 

Key Conclusions 

• Simulations are poised to benefit the design of real combustion devices. 

• The set of evaluated fundamental data for use in these simulations is incomplete. 

• Major gaps exist in the understanding of combustion chemistry specific to real fuels. 

• Mixtures comprised of compounds from six chemical classes can be used to formulate 

a spectrum of useful surrogate fuels. 

• A complete description of the combustion chemistry for real fuels would be 

prohibitively large and, thus, reduced chemical kinetic models must be developed. 

• The lack of information exchange standards is a major barrier to advancement. 

• Strong collaboration is imperative and requires a suitable infrastructure. 

• The combustion community wishes to develop a research roadmap that focuses its 

efforts for advancing combustion research. 
 ix

iv. Evaluation of the data should be a collaborative project among a wide range of 

experts in the area of chemical kinetics. 

3) There are major gaps in our knowledge of the combustion chemistry of real liquid 

transportation fuels. This is because real fuels involve large, complex molecules, and 

because real fuels can contain hundreds of constituents. 

i. Because large molecules undergo a sequential reduction in size during 

combustion, simulations of real fuels must include and will be built around 

existing chemical kinetic models that detail the chemistry of small (C1 to C3) 

hydrocarbons. 

ii. "Small molecule" chemistry must be extended to include the relevant chemistry of 

the larger species present in transportation fuels. These include pyrolytic cracking 

and oxidation reactions that convert large molecules to small, and several classes 

of condensation reactions that govern the growth of polycyclic aromatic 

hydrocarbons (PAHs) and soot. Although some reasonable estimations of the 

chemistry are possible with the currently available knowledge, benchmark 

experiments are needed to validate these estimations, to provide insight into 

chemistry not yet accessible by theory, and to provide high accuracy values for 

the most crucial reactions. 

iii. An understanding of the kinetics and chemical kinetic models of fuel combustion 

is crucial to the continued development and improvement of key emerging 

technologies (e.g., homogeneous charge compression ignition (HCCI) engines). 

4) There is some consensus on how to formulate surrogates for real fuels that will aid 

experiments and computational simulations: 

i. Six chemical classes were identified that are presumed to encompass the minimal 

set of constituent types necessary to describe the hydrocarbon chemistry of real 

transportation fuels. For the six classes there is a (reasonable) consensus as to 

specific model compounds whose combustion chemistry, if reliably determined, 

would advance the simulation of the combustion of real fuels. 

ii. There is no one surrogate 

mixture that will address 

all the testing and research 

needs for diesel, gasoline, 

and jet fuels or apply to all 

of the numerous different 

combustors of interest, but 

surrogates for all fuels 

could reasonably consist 

of distinct formulations of 

the six model compounds. 

Workshop Consensus for Chemical 

Constituents of Surrogate Fuels 

• Iso-paraffins: Iso-octane 

• Normal paraffins: Heptane, Hexadecane, 

Decane 

• Single ring aromatics: Toluene, Xylenes 

• Cyclo-paraffins: Methylcyclohexane 

• Olefinic species: 1-Pentene 

• Multi-ring aromatics: 1-methylnapthalene
 x

iii. The cost of pure-compound-based surrogate fuels remains a serious concern to 

researchers and engine developers who require large quantities of fuel. 

Nonetheless, it was generally believed that surrogate fuels would be useful for 

testing and modeling purposes and would aid in our understanding of the related 

"reference fuels" commonly used in engine design and specification. 

iv. In addition to the hydrocarbon surrogates, surrogates for sulfur containing 

impurities, oxygenate additives, and anti-knock agents may be needed. 

5) The combustion problem is multi-scale, ranging from atoms and molecules to particulates 

and devices (e.g., engines and turbines). Successful treatment of combustion problems is 

necessarily multi-disciplinary. 

i. Accurate chemical kinetics models that reproduce the combustion characteristics 

of real devices need to be quite complex and this requirement makes them more 

costly to compute. 

ii. To produce accurate results, CFD simulations need to incorporate accurate kinetic 

rate coefficients; however, current CFD codes can only incorporate a small subset 

of the total reaction set. 

iii. The current best practice is to create reduced chemical kinetic models that capture 

the essential features of the combustion problem being studied. Each reduced 

chemical kinetic model needs to be derived from a larger chemical kinetic model 

that is validated against experimental data sets collected over a broad range of 

conditions. 

iv. Producing a chemical kinetic model for combustion requires access to accurate 

thermodynamic and chemical kinetic data for many chemical species. It is a 

practical impossibility to measure or compute all of the fundamental data 

required. Clearly an 

approach that focuses the 

greatest effort on the most 

important chemical 

species and their reactions 

is appropriate. Likewise, 

model parameters shown 

by mathematical analysis 

to be less important are 

permitted to have larger 

uncertainties and may be 

estimated. 

6) The absence of a commonly understood and accepted terminology for describing and 

quantitatively specifying combustion chemistry is a significant barrier to realizing the 

benefits of computer-aided design and inhibits the sharing of information among 

researchers. 

Chemical Kinetic Models of 

Combustion Become Complex 

as "Real Fuels" are Approached 

 Model # Species # Reactions

 O2 + H2 8 27 

 O2 + Methane 34 210 

 O2 + iso-Octane 860 3600 
 xi

i. Even in areas for which there is little dispute as to the physical or chemical 

meaning of the information, there are no accepted standards for the exchange of 

the required information. 

ii. At present there are no commonly understood and agreed upon descriptors for the 

information required to quantitatively represent a chemical kinetic model and no 

information exchange standards that would allow facile and reliable exchange and 

widespread use of combustion simulation models. 

7) The current absence of strong and effective collaboration, limited at least partly by the 

lack of an appropriate infrastructure for collaboration, is a major impediment to reaching 

the goal of simulation-based combustor design. This collaboration will require full 

access to a common set of data, models, benchmark test information, and a wide variety 

of tools. 

i. There was general agreement that internet-based collaboration would be valuable 

and widely used. The goal of the Collaboratory for Multi-Scale Chemical Science 

(CMCS) to develop an adaptive informatics infrastructure to enhance data 

management, data sharing, and scientific collaboration was broadly supported. 

ii. There was also general agreement that the establishment of a commonly 

accessible repository of data validated by consensus of the community would be 

beneficial. 

iii. NIST was cited as a logical center for such operations, and the attendees were 

very interested in NIST playing a central role in facilitating the provision of data 

required for the collaboration. 

8) There is need for the creation of a carefully planned roadmap by the combustion 

community. The roadmap should establish well-defined goals and a means to achieve 

those goals as a community. 
 xii
 1

WORKSHOP REPORT 

I. Introduction 

On September 4th and 5th the NIST Chemical Science and Technology Laboratory hosted the 

"Workshop on Combustion Simulation Databases for Real Transportation Fuels" at its 

Gaithersburg, MD campus. Approximately sixty expert scientists and engineers, drawn evenly 

from industry, academia, and government (including military), attended the meeting. The 

objective of the workshop was to assist NIST and the combustion community in formulating a 

plan for developing databases and chemical kinetic models for simulating the combustion of real 

liquid fuels. The workshop was organized in response to the recognized overwhelming 

importance of energy to the United States economy, the increasing need to optimize combustion 

processes for efficiency and pollution minimization, and to address the increasing role of 

computer simulations in all areas of design. Modern computational fluid dynamics (CFD) codes 

are of great potential value because they may accelerate research and engineering projects that 

will design novel, efficient, less polluting combustion devices and improve older ones. 

Statistics provided by the Energy Information Administration1

 (EIA) indicate that the United 

States consumed 29 trillion kilowatt-hours (29 × 1012 kW-h) of energy during 2002. Of this total, 

86 % was derived from fossil fuels, 8 % from nuclear electric sources, and 6 % was classified as 

renewable energy. The EIA predicts that combustion of fossil fuels will remain the primary 

source of energy in the U.S. for decades to come. Domestic fossil fuel sources of energy are 

petroleum products (45 %), natural gas (28 %), and coal (27 %). The NIST workshop 

concentrated on technology that can improve the combustion of liquid petroleum fuels in 

turbines and engines, which are used 

mainly by the transportation sector of the 

economy. These power sources are also 

used in construction and stationary 

power equipment. 

Since energy consumption is a local ondemand activity, the associated 

consequences of fuel combustion cannot 

be exported. The related economic, 

environmental, and health effects impact 

the entire population of the United 

States. In 2000 industry and consumers 

spent $272B for transportation fuels.2-4

 

1

 Energy Information Administration, Table 1.3 Energy Consumption by Source, Monthly Energy Review, available 

on-line: http://www.eia.doe.gov/emeu/mer/overview.html. 2

 Energy Information Administration, Annual Energy Review, Table 5.12c Petroleum Consumption: Transportation 

Sector and End-Use Total, 1949-2002, available on-line: http://www.eia.doe.gov/emeu/aer/txt/stb0512c.xls and 

http://www.eia.doe.gov/emeu/aer/petro.html. 

 Liquid Transportation Fuel Usage (2000) 

 

 Sector 109

 liter/yr(a Cost(b 

Gasoline 488 $191.7B

Diesel 141 56.8B

Jet Fuel 101 23.6B

Aviation Gas 1 0.4B

 Source: 

Derived using DOE source data from: a) Ref. 2. 

b) Ref. 3. 

NOTE: Ave. 2000 domestic crude oil price: $26.73/barrel (Ref. 4). 
 2

In industry, energy costs are a major concern in production processes. Increased efficiency 

translates directly to greater economic competitiveness in the global marketplace. Even very 

small improvements in efficiency will result in vast savings. For example, the homogeneous 

charge compression ignition (HCCI) engine, which is one of several advanced concepts under 

development, offers a 33 % improvement in peak combustion efficiency over current sparkignition engines.5-6 Calculated with 2000 average fuel prices,4

 the emergence of such engines, 

enabled by a thorough understanding their combustion chemistry,6

 could potentially reduce 

annual domestic automobile fuel costs by $50B/year. 

Improved efficiency would lower CO2 emissions, which are strongly linked with global climate 

change and may be expected to see increasing national and international scrutiny and regulation. 

For example, the current voluntary reporting7

 of greenhouse gases (GHG) under section 1605(b) 

of the Energy Policy Act of 19928

 is widely expected to lead to mandatory regulations and 

international trading of GHG credits. 

The costs to the nation associated with environmental effects related to combustion are large. In 

its recent report to congress on the benefits and costs of the clean air act, EPA analysis suggests a 

net benefit to the nation of approximately $62B/year resulting from air quality improvement, 

largely through the reduction of pollutants associated with the combustion of fossil fuels.9

 

Particulate matter produced by transportation engines is a major concern due to its possible 

health and environmental consequences. Several studies that have established10-14 a link between 

particulate matter and asthma and cardiovascular disease. These adverse health effects result 

 3

 Energy Information Administration, Table 5. Transportation Sector Energy Price and Expenditure Estimates, 

Selected Years 1970-2000, United States, State Energy Statistics, available on-line: 

http://www.eia.doe.gov/emeu/states/sep_prices/tra/pr_tra_us.html. 

4 The average domestic crude oil price during 2000 was $26.73/barrel: Energy Information Administration, Table 9.1 

Crude Oil Price Summary, Monthly Energy Review, Mar 2001 

(http://tonto.eia.doe.gov/FTPROOT/multifuel/mer/00350103.pdf and http://www.eia.doe.gov/mer). 5

 K. Epping, S. Aceves, R. Bechtold, J. Dec, The Potential of HCCI Combustion for High Efficiency and Low 

Emissions, Society of Automotive Engineers, Inc. (Warrendale, PA), SAE Paper 2002-01-1923. 6

 Science & Technology Review, Apr 2004, (http://www.llnl.gov/str/April04/April04.html). 7

 See for example: Energy Information Administration, Voluntary Reporting of Greenhouse Gases 2002, DOE/EIA0608(2002), (Washington, DC, January 2004), (http://www.eia.doe.gov/oiaf/1605/vrrpt/index.html). 8 Energy Policy Act of 1992, Section 1605, National Inventory and Voluntary Reporting of Greenhouse Gases,

Voluntary Reporting of Greenhouse Gases Communication Center (http://www.eia.doe.gov/oiaf/1605/policy.html). 9 The Benefits and Costs of the Clean Air Act 1990 to 2010: EPA Report to Congress, Table ES-1 (EPA central 

value converted to year 2000 dollars), EPA-410-R-99-001, U.S.EPA, 1999 (http://www.epa.gov/oar/sect812/). 10 M. Lipsett, S. Campleman, Occupational Exposure to Diesel Exhaust and Lung Cancer: A Meta-Analysis,

American Journal of Public Health 89, 1009-1017 (1999). 11 W. Stober, U. R. Abel, Lung Cancer Due to Diesel Soot Particles in Ambient Air? A Critical Appraisal of 

Epidemiological Studies Addressing This Question, International Archives of Occupational and Environmental 

Health 68, S3-S61 Suppl. S (1996). 12 A. Peters, D.W. Dockery, J. E. Muller, and M. A. Mittleman, Increased Particle Air Pollution and Triggering of 

Mycardial Infarction, Circulation 103, 2810-2815 (2001). 13 S. Boland, A. Baeza-Squiban, F. Marano, Respiratory Toxicity of Diesel Exhaust Particles: Cellular and 

Molecular Mechanisms, M S-Medecine Sciences 17, 596-603 (2001). 14 Environmental Protection Agency 40 CFR Part 50 [AD–FRL–5725–2] RIN 2060–AE66, National Ambient Air 

Quality Standards for Particulate Matter, Federal Register 62 (No. 138), Jul 18, 1997, 38652-38760 

(http://homer.ornl.gov/oepa/rules/62/62fr38652.pdf). 
 3

Figure 1. Progress in reducing particulate emissions from engines as 

improvements were incorporated (right to left). Blocks outline the past 

and future EPA emission regulations governing engines. Adapted from 

J. Dec, Sandia Combustion Research Facility.

from deposition and 

subsequent actions of 

particles in the thoracic 

(tracheo-bronchial and 

alveolar) portions of the 

lower respiratory tract. 

Particulates and 

associated subsequent 

chemistry also have 

deleterious effects15 on 

vegetation and ecosystems, visibility, and 

man-made materials 

used in construction. 

Acting on these findings, the United States 

Environmental Protection Agency (EPA) has 

issued National Ambient 

Air Quality Standards 

(NAAQS) for 

Particulate Matter (PM) 14. The air quality standards, known as PM10 and PM2.5, set maximum 

allowable ambient concentrations permitted for particle sizes ≤ 10 μm diameter (10 microns) and 

particle sizes ≤ 2.5 μm diameter, respectively. Every five years the PM10 and PM2.5 standards are 

reviewed and may be revised under the U.S. Clean Air Act. In addition to standards for 

particulate matter, the EPA continues to set standards for regulation of other combustionproduced pollutants such as NOx and SO2. 

Figure 1 charts the stepwise reductions of allowable NOx and particulate matter emission from 

engines permitted under EPA regulation since 1978. Hollow circles and arrows plot the reduction 

in emissions from research engines as mechanical and operational improvements have been 

incorporated over the past 24 years. The tiny black box at the X-Y origin depicts the EPA 

stipulated NOx and PM emission levels that new engines must meet for the 2007-2010+ model 

years.16

As engineers try to design engines that comply with increasingly stringent (EPA or international) 

emission regulations, they must confront, in more detail, the components of an enormous 

multivariate problem that spans mechanics, fluid dynamics, and chemistry. Research has 

revealed that engine efficiency, NOx generation, and particulate matter production are largely 

governed by complex interactions between the fluid dynamics and the fundamental combustion 

 

15 L. Yang, I. Stulen, L. J. De Kok, Y. Zheng, SO2, NOx and Acid Deposition Problems in China Impact on 

Agriculture, Phyton-Annales Rei Botanicae 42, 255-264 (2002). 16 Control of Air Pollution from New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards and Highway 

Diesel Fuel Sulfur Control Requirements, Federal Register: Jan 18, 2001 (Vol. 66, No. 12), [Rules and Regulations, 

Pages 5001-5050] (http://www.epa.gov/fedrgstr/EPA-AIR/2001/January/Day-18/a01a.htm). 
 4

chemistry of fuel oxidation. Therefore, scientists believe that computer simulations that account 

for these interactions explicitly will become an important tool for designing more efficient, less 

polluting combustion devices. Since studies also indicate that the microscopic details of the 

combustion chemistry govern emissions, simulations of engine performance will require CFD 

codes that incorporate sophisticated chemical kinetic models in order to reproduce the important 

features of real fuel combustion. 

The formulation of chemical kinetic models of fuel combustion is a fundamental research topic 

for which the state-of-the-art is constantly evolving. Chemical kinetic models are living entities 

that improve in accuracy and usefulness as additional chemistry is added. The complexity of real 

fuels will require the construction of models that are vastly larger in size than models devised 

previously for the combustion of simple fuels. While it was possible for one person to compile a 

satisfactory model for hydrogen combustion and a small group to compile the model for methane 

combustion, it will require a community to build models for real fuels. The previous construction 

of the GRI-Mech17 and stratospheric ozone18 databases have demonstrated that a large committee 

of scientists can work together in support of large models for important problems. This workshop 

found consensus that modern experimental capabilities, recent theoretical developments, and 

novel web-based infrastructure concepts can make the construction of comprehensive models for 

real fuel combustion feasible. 

II. Session Presentations 

The following summarizes the presentations and discussions presented at the meeting. The 

presentations spanned four broad headings: Physical and Chemical Property Data, Fuels and 

Surrogates, Simulations and Chemical Kinetics, and Community Collaboration. The topics and 

order of this report reflect the workshop program schedule during a two-day meeting. Each 

section presents an overview of the presentations and summaries the consensus of the 

participants. Individual talks are also summarized and reflect the individual opinions of each 

presenter. 

It became clear from the presentations and discussion at the meeting that many commonly used 

terms have slightly or even very different meanings to various researchers in the field. This in 

itself is a good illustration of some of the current difficulties in sharing information within the 

community. The Glossary at the end of this text provides definitions of terms as used in this 

document. 

 

17 GRI-Mech Home Page (http://www.me.berkeley.edu/gri_mech). 18 S. P. Sander, R. R. Friedl, A. R. Ravishankara, D. M. Golden, C. E. Kolb, M. J. Kurylo, R. E. Huie, V. L. Orkin, 

M. J. Molina, G. K. Moortgat, B. J. Finlayson-Pitts, Chemical Kinetics and Photochemical Data for Use in 

Atmospheric Studies, Evaluation Number 14 of the NASA Panel for Data Evaluation, JPL Publication No. 02-25, 

Feb 2003 (http://jpldataeval.jpl.nasa.gov). 
 5

A. Physical and Chemical Property Data 

1. Overview 

Correct models of combustion systems require access to an enormous volume of physical and 

chemical information. The workshop examined the current state-of-the-art of the supporting 

databases and discussed the features of future databases that will facilitate simulations involving 

real fuels. Workshop discussions were posed with the postulate that future databases will be 

accessible through an Internet interface. 

The physical property data needed for combustion modeling of liquid fuels includes thermal 

conductivity, viscosity, surface tension, vapor pressure curve, heat capacity, density (P-V-T), and 

speed of sound over a range of temperature, composition, and pressure. The chemical data 

includes thermochemical data 

( o ∆f H , o S , o Cp , etc.) for fuel components and reaction intermediates as 

functions of temperature and pressure. 

In addition to the numeric values listed 

for these properties, these data must be 

traceable, i.e., the data source and 

property uncertainties are provided. 

Many participants indicated a strong 

preference for databases of critically 

evaluated (recommended) data, due to 

their reliability and self-consistency. 

Several speakers also expressed a need 

for increased integration among 

databases. 

As combustion simulations have 

considered more complex fuels, the 

number of chemical constituents and 

number of reactions have increased 

dramatically. The accompanying table shows the number of species and reactions required to 

describe the combustion of simple fuels, hydrogen and methane17, and smaller real fuels, 

heptane19 and iso-octane20. Models increase rapidly in complexity as the molecular weight of the 

fuel increases. The model size is further increased by accounting for additional combustion 

features such as polycyclic aromatic hydrocarbon (PAH) production. 

For larger chemical species, a simple assemblage of elementary chemical reactions and rate 

coefficients will be no longer possible because direct measurements are unavailable. There is, 

 

19 H. J. Curran, P. Gaffuri, W. J. Pitz, and C. K. Westbrook, A Comprehensive Modeling Study of n-Heptane 

Oxidation, Combustion and Flame 114, 149-177 (1998). 20 H. J. Curran, P. Gaffuri, W. J. Pitz, and C. K. Westbrook, A Comprehensive Modeling Study of iso-Octane 

Oxidation, Combustion and Flame 129, 253-280 (2002). 

Chemical Kinetic Models of 

Combustion Become Complex 

as "Real Fuels" are Approached 

 Model # Species # Reactions

 O2 + H2 8 27 

 O2 + Methane 34 210 

Real Fuelsa:

 O2 + Heptane 540 2450 

 O2 + Heptane/PAHb

 625 2700 

 O2 + iso-Octane 860 3600 

 O2 + iso-Octane/PAHb

 935 3850 

a

Refs. 19, 20. b

Includes production of PAH soot precursors.
 6

however, a great deal of understanding in terms of algorithms with predictive or extrapolative 

properties. The conversion of this "understanding" to rate expressions and thermodynamic 

properties with known uncertainties is not a trivial task, but it is being actively addressed by the 

research community. 

Constructing combustion models of large hydrocarbons reveals major gaps in our knowledge of 

the reaction chemistry of real liquid transportation fuels. These gaps exist because real fuels 

involve large, complex molecules and because common real fuels contain hundreds of 

constituents. Because large molecules undergo a sequential reduction in size during combustion, 

simulations of real fuels must also include chemical kinetic models that detail the chemistry of 

small hydrocarbons. Some of these data are available for C1 to C3 species, but this "small 

molecule" chemistry must be extended to include the relevant chemistry of the larger species 

present in transportation fuels, particularly reactions that convert large molecules to small. The 

needed chemistry may be categorized in terms of pyrolytic cracking, oxidation, and condensation 

reactions that govern the growth of polycyclic aromatic hydrocarbons and soot. 

One of the most important aspects of creating these databases is the increasing reliance on theory 

to generate the necessary information. This reflects our increasing fundamental understanding of 

the physical and chemical interactions. The demonstrated utility and reliability of theoretical 

methods is a fortunate recent development, since it is impractical to directly determine 

experimentally all the data that are needed. New methods for estimating unmeasured elementary 

rate coefficient data continue to be actively pursued research topics. Although the predictive 

capabilities of many of the existing algorithms are impressive, experiments are still needed to 

validate particular estimations, to provide insight into chemistry not yet accessible by theory, and 

to provide high accuracy values for the most crucial reactions. 

Participants noted that the dearth of critically evaluated thermochemical, kinetic, and transport 

data severely hampers the development of predictive chemical models and simulations for 

combustion. The combustion literature contains many chemical kinetic models, many of which 

are internally inconsistent, are in conflict with other established models, or contain chemical 

kinetic rate coefficients that can be easily shown to be incorrect. A large fraction of the 

thermochemical, thermophysical, and reaction rate data used in chemical kinetic modeling has 

not been compared to evaluated data, nor systematically checked for self-consistency. There is 

no generally accepted set of results on experimental systems that can be used to inter-compare 

and refine chemical kinetic models. 

2. Individual Talks21

John Farrell (Exxon Mobil Corp.) presented at talk entitled "Gasoline Composition." He 

described the classes of compounds contained in gasoline, the predominant individual 

components, how the proportions can vary significantly due to many factors, and how the exact 

composition of gasoline is driven by both performances needs and regulatory criteria. He 

provided an overview of gasoline derived from crude oil. 

 

21 Speakers usually addressed two or more subtopics. To avoid fragmentation, this report summarizes each 

presentation completely under the dominant report subheading addressed by the talk.
 7

10

8

6

4

2

0

Mole Percent

2 4 6 8 10 12

Carbon Number

 n-paraffins

 i-paraffins

 naphthenes

 aromatics

 olefins

olefins

aromatics

n-paraffins

i-paraffins

naphthenes

10

8

6

4

2

0

Mole Percent

2 4 6 8 10 12

Carbon Number

 n-paraffins

 i-paraffins

 naphthenes

 aromatics

 olefins

olefins

aromatics

n-paraffins

i-paraffins

naphthenes

Figure 2. The composition of gasoline showing the relative 

amounts of each chemical class and the distribution of carbon 

numbers within each class. Adapted from J. Farrell, Exxon Mobil 

Corp.

Although the nascent composition of crude oil is peaked toward the high boiling point diesel and 

lubricating oils, the commercial demand is peaked towards gasoline. The exact composition of 

gasoline is driven by both performance needs and regulatory criteria. Emission driven 

requirements include physical properties such as volatility and stability, limits on levels of 

carcinogens, aromatics, and olefins, and the addition of oxygenates. Performance driven criteria 

include octane number, easy startup, and low tendency to vapor lock. 

The composition of gasoline is extremely dependent upon the origin/location of the crude, the 

specific refinery, and other factors including seasonal needs (e.g., relative volatility) and streams 

extracted for the chemical industry. Crude contains largely paraffins, naphthalenes, and 

aromatics. Gasoline is a blend from many different refinery streams containing different 

percentages of the types of major components. 

The composition of real fuels is 

tailored to minimize refinery costs 

and to comply with regulatory 

restrictions. Real fuels contain olefins 

simply because they are by-products 

of the refinery process. Due to the 

carcinogenic properties of benzene, 

streams of aromatics are processed to 

maintain low levels of benzene 

(< 1 %). To meet requirements of the 

Clean Air Act of 1990,22

reformulated gasoline contains added 

oxygenates, either ethanol or methyl 

tert-butyl ether (MTBE). 

Although the exact composition of 

gasoline is complex and varies 

considerably, one can provide a list 

of representative molecules for each 

type of component based upon abundance: aromatics (toluene, m-xylene), normal paraffins (nbutane, n-pentane), isoparaffins (methyl butane, methyl pentane, isooctane), naphthalenes or 

cycloparaffins (methyl cyclopentane, cyclohexane), olefins (methyl butene, methyl pentene), and 

oxygenates (ethanol). 

Daniel Friend (National Institute of Standards and Technology) presented the talk, coauthored by M. Huber, E. Lemmon, R. Perkins, and J. Magee, entitled "Thermophysical 

Properties of Real Fuels." His talk presented an overview of past and present work and 

capabilities at NIST with regard to measurements, calculations, modeling, and databases for 

thermophysical properties of fluids with a particular emphasis on those related to hydrocarbon 

fuels. 

 

22 Clean Air Act as amended in 1990, U.S. Environmental Protection Agency 

(http://www.epa.gov/air/oaq_caa.html). 
 8

NIST has developed and maintains of a number of relevant thermophysical databases; these 

include the NIST Standard Reference Databases NIST-4 (SUPERTRAPP - Thermophysical 

Properties of Hydrocarbon Mixtures), NIST-12 (Thermodynamic and Transport Properties of 

Pure Fluids), NIST-14 (Mixture Property), and NIST-23 (REFPROP - Reference Fluid 

Thermodynamic and Transport Properties), as well as the TRC Thermodynamic Tables. NIST 

has capabilities for high precision measurements of thermophysical properties over a wide range 

of pressures and temperatures for single component and mixtures in liquid, vapor, and 

supercritical phases. This includes the ability to prepare well-defined and well-characterized 

mixtures. NIST has apparatus for high precision measurements of properties such as thermal 

conductivity, viscosity, surface tension, heat capacity, density (P-V-T), and speed of sound. 

Implicit to these thermophysical databases at NIST is the ability to accurately model the 

properties of fluids over a wide range of pressures and temperatures. Relevant data span mixtures 

consisting of different components and mixtures of more than one phase. 

This talk discussed some of the requirements for accurately modeling the thermophysical 

properties of complex fluids such as real fuels and some of the advances needed in this area. A 

database connecting physical and chemical properties would be a significant breakthrough. One 

of the conclusions was that a strong coordinated program could achieve major impact in design, 

development, and optimization of combustion systems. To achieve this goal, Friend suggested 

that it would be necessary to develop extensive collaborations among industry, academia, and 

governmental agencies. Industry can help this process by defining the scope of data needs with 

regard to systems, ranges, and uncertainties. NIST can take a lead in areas where data standards 

are required. 

M.C. Lin (Emory University) presented a talk, co-authored by R. Zhu, entitled "Ab Initio 

Studies of NCN Reactions with O, OH and O2." He described recent work on the oxidation of 

NCN. This represents a new interpretation of the mechanism for prompt NO formation and 

demonstrates the power of modern computational techniques. The ab initio calculations and 

RRKM rate predictions presented in this talk highlighted the issue of "what is an elementary 

reaction?" The examples given in the talk showed how the rate of reaction of an apparently 

straightforward A+B=C+D bimolecular reaction can arise from the sum of several different 

channels that contain multiple short-lived intermediates and several nearly iso-energetic 

transition states. The overall reaction can be influenced by association steps and operate 

simultaneously on potential energy surfaces of differing spin multiplicity.

Wing Tsang (National Institute of Standards and Technology) presented the talk entitled 

"Combustion Simulation Databases for Real Transportation Fuels." His talk presented a review 

of the chemical database needs for real fuels with explicit consideration given to the presence of 

larger alkanes. The general picture involves four general reaction types: a) pyrolytic cracking 

forming smaller species, b) oxidative cracking forming smaller species, c) soot formation from 

unsaturated compounds, and d) oxidation of the species formed by cracking processes. 

Without making judgments on their quality, kinetic databases for soot formation and oxidation of 

the smaller species can be found in the literature. Chemical kinetics databases also exist for the 

oxidative cracking of fuels up to decane. This highlights the need for information on pyrolytic 
 9

cracking of smaller fuels and, in general, the breaking down of the larger fuels to smaller 

fragments by pyrolysis or oxidation. 

Some problems and solutions for building cracking databases for the larger fuels were discussed 

in the talk. It was pointed out that for large alkanes, the resulting database must contain reactions 

for the decomposition of all of the smaller linear alkyl and 1-olefinyl radicals. An experimental 

methodology for building a chemical kinetic model for the pyrolytic cracking of n-alkanes and nalkyl radicals was presented. This takes advantage of the availability of the n-alkyl iodides and 

large normal alkanes as sources for the generation of appropriate precursors. The situation is 

more unfavorable for branched alkyl radicals due to the possible need for numerous custom 

syntheses. In terms of elementary reactions, the key missing elements are the isomerization 

reactions involving radicals. 

B. Fuels and Surrogates

1. Overview

Transportation fuels, gasoline, jet fuel, and diesel, are refined products from the processing of 

crude oil. The composition of each fuel is driven by performance needs (e.g., octane/cetane 

numbers), regulatory-driven criteria for physical properties (e.g., vapor pressure, flash point), 

and economic factors imposed by the refining process and feedstock. These circumstances 

produce fuels that contain hundreds of chemical compounds in amounts that vary considerably. 

To attain consistent test results, industry uses reference fuels to assess engine-operating 

parameters, both for design purposes and for demonstration of performance related to regulatory 

requirements. Reference fuels may be specified by domestic or international governmental 

regulating agencies. These specifications vary by region. Reference fuels are usually needed in 

very large quantities, making it impractical to replace them with pure component mixtures. 

Although reference fuels will always be needed at some stage in the engine design and testing 

process, workshop participants felt that laboratory studies and simulations based on surrogate 

fuels would be more reproducible and facilitate deeper insights into combustion processes. The 

participants believe that data derived with surrogate fuels could significantly reduce some of the 

current needs for expensive, large-scale testing. 

The community defines surrogates as a set of compounds whose relative concentrations can be 

adjusted so that the chemical and physical properties pertinent to combustion approximate those 

of a real fuel. A properly composed surrogate fuel should share nearly the same chemical 

kinetics and thermodynamic properties as the real fuel it simulates. The physical properties that 

surrogates should match include vapor-liquid-equilibrium, viscosity, surface tension, ignition 

delay, smoke points, and thermal stability. In this context, it is likely that absolute matches of all 

physical properties may not be achieved, but nonetheless, the consensus is that surrogates can 

serve as a useful proxy for reference fuels. 
 10

The workshop presentations gave evidence for the feasibility of surrogates that match the 

combustion properties of real fuels. Although each fuel type contains hundreds of chemical 

compounds, these compounds are members of only a few chemical classes: alkanes, 

cycloalkanes, aromatics and olefins. Each of these compounds does not itself make a unique 

contribution to the combustion properties of a fuel. Experience has shown that despite the wide 

variations in the composition of fuel mixtures, fuel combustion properties, such as octane 

numbers (for gasoline) and cetane numbers (for diesels) are relatively invariant. However, some 

work remains in defining surrogate fuel specifications. For example, data that define the soot and 

PAH characteristics of real fuels and surrogate candidates are needed. 

The workshop outlined some steps 

toward filling the major information gaps 

for real fuels. The six chemical classes 

identified at the workshop are presumed 

to constitute the minimal set of 

constituent types necessary to describe 

the chemical composition of real fuels 

used by the trucking, construction, 

aviation, and personal transportation 

sectors. No one surrogate mixture is 

expected to address all the testing and 

research needs for diesel, gasoline, and 

jet fuels or for the many different 

combustors of interest. But surrogates for all fuels could reasonably consist of different 

compositional mixtures of the six model compounds. There is an initial working consensus as to 

the specific model compounds whose combustion chemistry, if reliably determined, would allow 

simulation of the combustion of real fuels. These choices should be further reviewed as relevant 

data become available and may well see refinement. 

The cost of pure-compound-based surrogate fuels remains a serious concern to researchers and 

engine developers who require large quantities of fuel. Nonetheless, it was generally believed 

that surrogate fuels would be useful for testing and modeling purposes and would aid in our 

understanding of the related "reference fuels" commonly used in engine design and specification. 

In addition to the hydrocarbon surrogates, surrogates for sulfur-containing impurities, oxygenate 

additives, and anti-knock agents may be needed. 

Surrogates for aviation fuels are already being tested. The degree to which they truly represent 

the properties of a real fuel is beginning to appear in the literature. Some results were reported at 

this workshop. 

In summary, the consensus of the workshop is that applying the concept of surrogate fuels is 

enabling. Mixtures of surrogate compounds can reproduce the combustion behavior of 

transportation fuels. Simulations that begin with a limited set of surrogate components will be 

more quickly computed. Finally, a limited set of surrogate compounds would allow a single 

database of chemical and kinetics properties to support combustion simulations relevant to all 

sectors of the transportation industry. 

Workshop Proposal for Chemical 

Constituents of Surrogate Fuels 

• Iso-paraffins: Isooctane 

• Normal paraffins: Heptane, Hexadecane, 

Decane 

• Single ring aromatics: Toluene, Xylenes 

• Cyclo-paraffins: Methylcyclohexane 

• Olefinic species: 1-Pentene 

• Multi-ring aromatics: 1-methylnapthalene
 11

2. Individual Talks21

William L. Brown (Caterpillar) presented a talk entitled "’Real’ Diesel Fuel - Caterpillar’s 

Story." He gave a brief overview of the specifications of diesel fuels. Although diesel engines 

operate on fuels of widely different composition, all fuels share high Cetane numbers. 

Customers and applications use many different diesel certification fuels. Each foreign national 

government also stipulates tests with specific certification fuels. 

Although 2-D is the most common commercial diesel fuel, Caterpillar uses many different 

certification fuels with tight specifications when developing engines. The talk also discussed in 

detail the development of HCCI engines and the inability of current chemical kinetic models to 

accurately simulate this low temperature system that contains slow reaction kinetics. Current 

simulations of sprays lack sufficient resolution in the CFD simulations. To achieve better 

simulations, full chemical kinetic models are needed that include the reactions describing NOx

and soot formation processes. 

Meredith B. Colket (United Technology Research Center) presented a talk, co-authored by 

Steve Zeppieri, entitled "Jet-A Surrogate Blends." His talk focused on the properties of 

surrogate mixtures used at UTRC and the important kinetics, physical, and chemical features that 

simulations should reproduce. Surrogate fuels should be formulated to match the physical and 

structural chemical properties of surrogate fuel. These properties should include the H/C ratio, 

molecular weight, vaporization temperature, viscosity, surface tension, aromatic content, and 

normal and branched and unbranched hydrocarbon fraction. 

For surrogate fuels chemical kinetic models should enable simulations to reproduce important 

combustion properties. These macroscopic kinetic properties include the light-off (ignition), 

auto-ignition, extinction, pyrolysis rates, soot production, conversion rate to CO, initial heat 

release rates and super-equilibrium radical concentrations. Data were presented on the 

equilibrium temperatures of a number of fuel mixtures. 

Tim Edwards (Air Force Research Laboratory) presented a talk entitled "Jet Fuel 

Composition." He detailed the composition of jet fuel, the range of variations possible due to 

broad specifications, and the differences among various jet fuels with regard to required physical 

properties such as flash point and freezing point, as well as with regard to additives. 

This talk gave a significant amount of information about the characteristics of jet fuel. Jet fuels 

are kerosenes. Even for specific jet fuels, batch-to-batch variations can be significant due to 

broad specifications. Commercial jet fuels are Jet A, Jet A-1, and Jet B. Jet B is a wide cut 

kerosene-gasoline (naphtha) mix that is highly flammable and has limited use in very cold 

climates having a very low freezing point compared to Jet A. Jet A and Jet A-1 are very similar 

with Jet A available only in the U.S. and Jet A-1 outside the U.S. They have the same flash point 

characteristics, but the international Jet A-1 has lower freezing point specifications. The most 

common military jet fuel is JP-8, which is the equivalent of commercial Jet A-1 but with 

additives. JP-4 is the wide cut military equivalent of commercial Jet B. JP-5 is very similar in 

characteristics and composition to JP-8, but has a much higher flash point and is used 
 12

predominantly by the Navy on aircraft carriers, due to its reduced flammability. Jet fuels are 

composed of a distribution of hydrocarbons that peak and center about C11-C12. For 

comparison, gasoline/naphtha distillates are composed of hydrocarbons that range up to C10-

C11. 

Specialty jet fuels such as JP-7, RP-1, and RG-1 are highly processed, clean kerosenes with high 

flash points. Compared to JP-8, these specialty jet fuels have very low aromatic and sulfur 

content and slightly higher hydrogen content. The composition of these fuels is typically 

restricted to C11-C14, as compared to JP-8, which ranges between C9-C15. Specifications for jet 

fuels are combinations of physical and chemical properties. For example, JP-8 hydrogen content 

must be > 13.4 % (H/C > 1.84), and is typically 13.8 ± 0.26 %; aromatics must be < 25 %, total 

sulfur < 0.3 % with < 0.002 % mercaptan sulfur; naphthalenes must be < 3 %; flash point 

> 100 °F (> 38 °C); and freezing point < -53 °F (< -47 °C). 

This talk also addressed the issues of surrogates and their composition compared to typical jet 

fuels, indicating that surrogate mixtures for jet fuels are practicable. The talk provided an 

overview of progress to-date and broad-reaching future plans to perform detailed gaschromatography mass spectrometry (GC-MS) chemical analyses of 57 jet fuel samples from 

sources worldwide; and current and future plans to store standard or typical jet fuels for use by 

others. 

David Lenhert (Drexel University) presented a talk, co-authored by D. Miller and N. 

Cernansky, entitled "Development and Evaluation of Fuel Surrogates in the Low and 

Intermediate Temperature Regime." He presented experimental results on the results of studies 

with surrogate gasoline and JP-8 mixtures using their pressurized flow reactor. The studies 

covered reactions in the low and intermediate temperature region. In this work they present 

reactivity maps (CO production versus temperature) for individual components, surrogate 

mixtures, and reference fuels. They developed a surrogate that matched reactivity maps for JP-8 

over a range of conditions. 

Adel Sarofim (Reaction Engineering and University of Utah) presented a talk entitled 

"Surrogates for Complex Fuels," that outlined criteria for the selection of surrogates. The talk 

outlined technical metrics for selection of surrogates including physical properties (e.g., boiling 

point) and fuel validation (e.g., burning rate). Sarofim also emphasized that the choice of each 

surrogate component should be directed to minimize the overall cost, as expensive surrogate 

fuels would not be widely used or accepted. 

Sarofim also presented overviews of work in the areas of measurements and modeling of 

surrogate fuels. Much of the past work on surrogates has to do with matching one or more 

properties. He reported that matching real fuel ignition properties is relatively easy by 

formulating mixtures composed of few compounds. However, formulating surrogates that match 

all desired physical and combustion properties simultaneously is very difficult. Sarofim 

described a new strategy for determining useful formulations. This method, structure oriented 

lumping, considers explicitly the chemical groups that comprise real fuels. In this approach, 

hydrocarbons in petroleum are characterized by sixteen chemical groups. Rules govern the 
 13

construction of the chemical reaction networks and group additivity rules account for the 

structural property relations. 

Very little data are available in the literature that compares the sooting properties of surrogate 

mixtures to those of real fuels. Sarofim reported observations on the GC patterns derived from 

soot fractions collected from JP-8. These patterns were compared with a surrogate mixture that 

matched the smoke point of JP-8. 

Mitchell D. Smooke (Yale University) presented a talk, co-authored by James Cooke, Matteo 

Bellucci, and Alessandro Gomez, entitled "JP-8 Surrogate Counterflow Diffusion Flames." He 

described recent results from experimental and modeling studies on counterflow diffusion flames 

using individual components, surrogate mixtures and JP-8. Detailed chemical kinetic models 

involving 220-260 species with 5000-7000 reactions were used. A six-component JP-8 surrogate 

(dodecane, isooctane, methylcyclohexane, tetradecane, tetralin and m-xylene) was used. Good 

agreement between predicted and measured temperature profiles (within about 100 K) and rich 

extinction limits (within about 10-20%) were observed. The differences are believed to reflect 

that experimental uncertainty and inaccurate specification of plug flow boundary conditions. 

C. Simulations and Kinetics

1. Overview

The Simulations and Kinetics presentations focused on the problems of simulating combustion 

systems with particular reference to the selection and use of surrogates. Computer simulations of 

real combustion devices span many length scales, ranging from atoms and molecules up to 

particulates and devices (e.g., engines and turbines). Accurate simulations require evaluated data 

formulated by experts from the chemical kinetics, thermodynamics, and fluid dynamics 

properties communities. 

The presentations demonstrated that computational fluid dynamics (CFD) simulations 

incorporating realistic fluid dynamics and chemistry are poised to be of great benefit in the 

design of real combustion devices, including diesel, HCCI, and jet engines. Presentations also 

showed promise that such simulations may accelerate the development of novel energy 

technologies, e.g., solid-oxide fuel cells and hydrocarbon reforming for hydrogen fuel 

technologies. 

Presentations showed that the development of new methods for deducing useful reduced 

chemical kinetic models is an actively pursued research topic. Such reduced models are needed 

so that the highly complex CFD simulations may fit within the resources available on 

supercomputers. Even if it were known, the complete reaction set describing the combustion of a 

real fuel would be too large for practical use in any simulation model. Likewise, most detailed 

initial reaction sets that describe the combustion of real fuels are also impractical. To remedy this 

resource conflict, research teams usually trim down the initial reaction set by deleting reactions 

that contribute little to the overall chemistry and/or by consolidating several elementary reactions 

into a smaller group of lumped reactions. Good practice includes validating each reduced model 
 14

against experimental data. Having detailed results of validated, well-defined, reference 

experiments available in a public database would be particularly helpful to the combustion 

community in its effort to validate new reduced models. 

Presentations pointed out the need for models that can predict simultaneously NOx and 

particulate matter production from diesel and HCCI engines. The simultaneous requirements for 

NOx and particulate matter minimization are in conflict since the high temperatures that are 

advantageous for particulate removal can lead to NOx formation, while the lower temperatures 

that reduce NOx production enhance particulate production. The need is to locate an optimum 

"window" where the most favorable tradeoffs occur. The HCCI engine, which promises to 

satisfy future emission standards and to give large energy savings, is a particularly interesting 

case. Because these engines operate under very lean conditions and lower temperatures than 

other engines, the chemical reaction rates of combustion are slower than for other engines. Thus, 

models must account for the chemical reaction process with greater detail. Models and measures 

developed for spark ignition engines (at much richer conditions and higher temperatures) have 

proved inadequate for predicting HCCI engine performance. 

The workshop identified a strong need for the creation of a database of chemical kinetic models 

and simulation models that have been validated for at least one set of combustion conditions. 

This database would help standardize model nomenclature, traceability, and data exchange 

protocols. The current lack of information exchange standards for communicating chemical 

kinetic models and validation data are slowing the development of chemical kinetic models for 

real fuels. At present, there are no agreed upon descriptors for the representation of information 

within models. Even in areas for which there is little dispute as to the physical or chemical 

meaning of the information, no accepted standards exist. These deficiencies impede the sharing 

of information among researchers and diminish the ability of the community to validate models. 

These deficiencies may also lead to the inadvertent proliferation of inaccurate mechanisms. 

2. Individual Talks21

C. Thomas Avedisian (Cornell University) presented a talk entitled "Toward a Standard for 

Evaluating Jet Fuel Kinetics." He discussed the use of a spherically symmetric droplet burning 

flame as a means of carrying out benchmark experiments for surrogate development. He also 

raised the interesting issue of determining the relative composition of a surrogate mixture that 

fits the particular application. Avedisian discussed some of the issues with regard to validation. 

He recommended the use of flow reactors, counter-flow diffusion flames, and shock tubes as 

benchmark configurations. He noted that ignition and extinction are the most sensitive features in 

combustion chemistry, but are strongly impacted by multi-dimensional transport phenomena. 

Thus, systems with 1-D transport are most important for validation studies. Avedisian discussed 

a burning droplet as an idealized one-dimensional system because droplets are spherically 

symmetric. He presented examples that showed measuring droplet diameter as a function of 

time as a useful metric for characterizing combustion systems. 

Anthony M. Dean (Colorado School of Mines) presented a talk entitled "Coupling Detailed 

Kinetics and Transport." The talk was co-authored by H. Carstensen, R. Kee, C. Sheng, K. 

Walters, and H. Zhu. He described the use of a fundamental hydrocarbon chemical kinetic 
 15

model (~ 400 species, ~ 2000 reactions) for simulating the direct electrochemical oxidation 

(DECO) of hydrocarbons in a solid-oxide fuel cell (SOFC) in a combined experimental and 

simulation study using butane as the fuel. 

The operational principles of the SOFC are complex, involving electron transport processes, 

electrochemical kinetics, heterogeneous chemistry, and hydrocarbon deposit formation. Since a 

SOFC typically operates at 700-1000 °C, one would expect that homogeneous cracking would 

also make a contribution. The kinetic model captured the strong temperature dependence of the 

butane conversion and correctly predicted the effects of dilution by N2 and H2O. Sensitivity 

analysis was used to determine a small subset of reactions that had the largest impact on butane 

conversion and other observables. 

The chemical kinetic model is in the process of being refined to include heterogeneous chemistry 

and electrochemical kinetics, as well as being coupled to an anode transport model. Although 

the application described is for direct combustion of hydrocarbons, this type of database will be 

invaluable for simulating the effect of additives on combustion, hydrocarbon cracking (the basic 

process for producing chemical feedstock) and indeed in any combustion based process. In all 

cases the proposed chemical kinetic model will describe the underlying process and thus form 

the basis for investigating what are essentially perturbations on the system. 

Frederick L. Dryer (Princeton University) presented a talk entitled "Some Remarks on Large 

Hydrocarbon Models and Surrogate Fuel Issues." He described the serious barriers to the 

construction of chemical kinetic databases suitable for the simulation of real fuels. These barriers 

include the absence of elementary data on the larger chemical reactants and intermediates and the 

absence of experimental data pertinent to the validation of chemical kinetic models of surrogate 

mixtures and real fuels. Dryer emphasized that detailed chemical kinetic models are never 

mathematically complete; therefore, the existing models are neither static nor unique. Instead, 

they are dynamic constructs that must be continually refined, optimized, and constrained as new 

data become available. Dryer noted that the very large size of typical chemical kinetic models 

makes simulations possible for only simple one-dimensional situations. 

Dryer presented a methodology for and examples of reaction set minimization and constraining 

procedures. He elaborated on the severe disconnects caused by the complexity of chemical 

kinetic models and the limited number of constraints available from validation data. From a 

statistical and parametric model point of view, this leads to a poorly posed minimization 

problem. This problem arises because initial chemical kinetic models contain many more free 

variables (usually 100’s of species and 1000’s of reactions) than can be constrained by a small 

number of experimental observables. Dryer recommended that the reduction processes should 

begin by selecting the validation data and then iteratively optimizing the reaction set through 

minimization of its dimensionality. 

Dryer expressed optimism regarding the use of surrogates and illustrated results based on threecomponent mixtures that are currently being used for engine testing. He recommended the use of 

primary reference fuel mixtures with an added aromatic (toluene) as a starting point for surrogate 

development. However, Dryer noted that the sub-models for toluene combustion have some 
 16

problems. This can have serious implications for soot/PAH simulations, since the standard 

employed databases for combustion have reactions that can be found in the former. 

Graham Goldin (Fluent, Inc.) presented a talk entitled "Chemical Kinetics in 

Multi-dimensional CFD," which summarized the present capabilities of CFD codes from Fluent, 

Inc. Combustion chemistry and modeling are important in different areas including internal 

combustion engines for automotive applications and gas turbines for power generation. 

Combustion modeling is particularly complex, because good models comprise complex 

chemistry, complex fluid dynamics, complex numerics (e.g., stiff differential equations, 

numerical errors, and convergence problems). 

Current computational methods attempt to strike a balance between simplified chemistry and 

simplified transport equations. CFD codes have been developed with the capability of handling 

the complex geometries found in real systems. This is, however, only realized with much simpler 

chemistry. Examples were presented that contained 15-20 species and 50-100 reactions. 

Examples were given with reduced reaction sets for a laminar diffusion methane-air flame, a 

methane-air rapid compression machine, a piloted turbulent jet methane/air flame, a lean 

premixed pre-vaporized propane/air flame, a combustor methane/air flame measured in an 

industrial combustor at Sandia’s Burner Engineering Research Laboratory, and a trapped vortex 

combustor methane/air flame. 

The developing computational technology of in situ adaptive simulations (ISAT) was discussed. 

ISAT may shorten computation time by an estimated 100-fold. During typical simulations, the 

stiff reaction rate equations are integrated millions of times. By building a table of mappings for 

the composition space, ISAT eliminates the need for repeating similar integrations. As a 

simulation approaches convergence, fewer new integration procedure calls are necessary because 

solutions are interpolated from mappings previously computed. Although ISAT and other 

developing numerical methods show promise for handling complex chemistry and transport, it is 

clear that in the near future, that there will still be a need for reduced chemical kinetic models. 

However, the general trend is clearly toward more species with a corresponding increasing 

number of reactions. 

Viswanath Katta (Innovative Scientific Solutions, Inc.) presented a talk entitled "CFD/large 

Chemistry Models: Unicorn 3.0 Code" that described a CFD code, UNICORN, that is being used 

at Wright Patterson Air Force Base in conjunction with an experimental program. Using only a 

conventional personal computer, they have been able to simulate two-dimensional complex 

flames with full chemistry, although with very long running times. Results for an impressive 

range of combustion situations were presented. The capabilities demonstrated by this modeling 

code suggest that combustion systems with reduced dimensionality can be completely described 

without the need for reduced chemical kinetic models. 

Chung K. Law (Princeton University) presented a talk entitled "Some Thoughts and Action 

Items on Mechanism Development for Combustion Applications." He described chemical kinetic 

model development in terms of the urgent need to have a realistic description of the events in 

combustion. In particular, Law was concerned with the proliferation and indiscriminate use of 

inadequate chemical kinetic models. He was also concerned with the enormous long-lasting 
 17

impact of training students to develop and utilize inadequate models, which propagates the 

problem. He emphasized that many of the individual elements necessary to achieve a realistic 

description of good models are in place, which he stated highlights the need for a detailed road 

map for combustion research. 

In addition to the need for further development of both detailed and reduced chemical kinetic 

models, Law emphasized the need for the development of a rigorous methodology for the semiautomatic generation and reduction of models. Such algorithms would be immune to changes in 

the reaction set, and thus, can provide a way of standardizing chemical kinetic models and assist 

in screening inadequacies in models. Law emphasized that the complexity of the chemistry and 

transport processes in combustion requires an integrated, comprehensive, multidisciplinary 

approach requiring significant broad-based education of students in this area. 

Gregory J. McRae (Massachusetts Institute of Technology) presented a talk, co-authored by 

Bill Green, entitled "Next Generation Reaction Modeling" that evaluated the state of the art in 

simulations and provided a detailed set of necessary next steps providing significant guidance to 

the community. He considered the aims of the present workshop in the context of the need for 

multi-scale integration. He (and others in the course of the workshop) pointed to the success of 

the biological community in successfully integrating individual data elements into large data sets 

that can be used for final applications. 

The talk provided an overview of current problems in practical applications covering a wide 

range of technology including hydrocarbon reformers, fuel cell technology, CVD, catalytic 

combustion for NOx reduction, and an overview of current databases used in reaction modeling. 

He highlighted the inadequacies in the current state of the art. These inadequacies include a lack 

of integration among databases, poor or no practical uncertainty estimates for the observed 

properties, poor documentation and traceability of data, and the absence of evaluated databases. 

McRae outlined many different advances needed in reaction modeling. Advances are needed in 

the identification and prioritization of research directions, rigorous statistical uncertainty 

analysis, rigorous determinations of the range of conditions over which models are valid, user 

friendly graphical interfaces for chemical kinetic model development, reduced model libraries, 

integration and exploitation of thermochemical and chemical kinetic data from quantum 

calculations and systematic benchmarking with experimental data. There is a strong need to 

semi-automatically generate chemical kinetic models by using rules for reaction types that are 

based on functional groups. Methods that use rate-based testing to determine relative importance 

are needed in order to constrain the number of species and reactions included in these chemical 

kinetic models. This approach would also help researchers determine when additional species 

and reactions must be added to a reaction set. 

The need for an organized effort by the entire community was stressed. The diversity of the 

combustion community makes organization with clearly stated goals in the form of road maps 

particularly important. The need is not only for data sets with clearly stated uncertainties, but 

also the tools to generate and manipulate data sets and libraries of reduced data sets that can be 

used directly. Success with regard to the next generation of reaction modeling will require a 

multi-disciplinary community providing a range of resources, knowledge, and views. Leveraging 
 18

input from each sub-community will require multi-scale integration among the private and public 

databases. To achieve this integration, robust standards for adequate representation of necessary 

physical and chemical data will need to be established. 

William J. Pitz (Lawrence Livermore National Laboratory) presented a talk entitled 

"Barriers to Developing Surrogate Mechanisms," which presented a summary of the practical 

problems with developing chemical kinetic models for the combustion of surrogate mixtures. 

Because such models are very large, Pitz believes that model reduction procedures must be used 

in order to make simulations feasible. Such reductions are difficult due to the scarcity of 

experimental thermodynamic and kinetic data for the chemical compounds that are likely to 

comprise surrogate mixtures. Although theory is becoming a more important tool, its actual use 

is time consuming and requires considerable judgment. The traditional way, based on a single 

investigator, of generating a reaction set is no longer a viable procedure given the enormous 

potential size and complexity of the models necessary to describe the pyrolysis and oxidation of 

large hydrocarbons, as well as PAH formation/destruction. 

Pitz pointed out that although combustion largely occurs on low-dimensional manifolds and is 

thus amenable to chemical kinetic model reduction, ignition and extinction are inherently multidimensional. This difference presents a fundamental problem for model reduction that may limit 

its application. Pitz also brought up an important question regarding model validation: when are 

disagreements between models and observables simply because small details in the boundary 

conditions have a large impact on the chemistry? When this situation arises, tweaking the 

chemistry to fit the observables is an incorrect procedure. In many cases, it is difficult to model 

or characterize the boundary conditions. Pitz provided an overview of some elements of the 

"bag of tricks" necessary for iterative model development 

Charles K. Westbrook (Lawrence Livermore National Laboratory) presented a talk, coauthored by Bill Pitz, entitled "Detailed Chemical Kinetic Modeling of Large Hydrocarbon 

Fuels." The objective of his current work is to provide validated chemistry models for 

combustion applications, including spark ignition engines, diesel engines, gas turbines, and the 

newest technology, HCCI. 

The presentation comprised a general discussion of the fuels (natural gas, gasoline, diesel, jet 

fuels) and the important chemistry for different temperature regimes. These represent important 

considerations for the selection of a surrogate. Westbrook detailed the complexity of the different 

fuels with regard to differing composition from fuel type to fuel type and even the wide range of 

compositions for individual fuels. He discussed the general issue of surrogates in the context of 

the differing chemical classes contained in the different fuel types. Westbrook summarized the 

problems and challenges involved in matching traditional measures of combustion properties, the 

Research Octane Number, with experimental results on ignition delays from the Rapid 

Compression Machine (RCM) and simulations. Generally, simulations match experimental 

results from the RCM. However, for the HCCI engine agreement between experiment and model 

predictions is very poor. This suggests that existing chemical kinetic models are incomplete in 

the very lean region. 
 19

D. Community Collaboration 

1. Overview 

Although the optimization of a specific geometry and design for a combustion device may 

represent an individual or even proprietary activity of a sponsoring organization, simulations of 

this device will incorporate a chemical kinetic model and other data that is not proprietary. For 

real fuels, most of this nonproprietary knowledge remains to be defined and optimized. Several 

speakers stressed the value of and need for increased community collaboration to solve the 

complex combustion problems involving real fuels. They noted that the current absence of 

effective mechanisms for developing multidisciplinary collaborations has impeded the 

improvement of simulation-based combustor designs. Most proposed that an effective 

mechanism would give access to a common set of data, chemical kinetic models, benchmark test 

information, and a wide variety of tools. 

Several web-based mechanisms for facilitating effective collaborations were presented, including 

the process informatics model (PrIMe) initiative and the Collaboratory for Multi-Scale Chemical 

Science (CMCS). Attendees generally supported the idea that these mechanisms would include a 

central repository for data that is validated through testing and discussions among the 

community. NIST was cited as a logical center for such operations, and the attendees were very 

interested in NIST playing an enabling role by facilitating the provision of data. The mechanisms 

and interactions of these central clearing houses and data operations across NIST, CMCS, and 

PrIMe would require integration by information technology experts and NIST scientists. The 

workshop attendees generally agreed that this comprehensive internet-based repository would be 

valuable and widely used. 

2. Individual Talks21

Michael Frenklach (Berkeley) presented a talk entitled "Development of Predictive Reactions 

Models." He outlined an approach for collaboration termed the Process Informatics Model 

(PrIMe). The aim of the project is to develop a community activity for development of reaction 

models of combustion. The initiative is a community effort to generate data libraries, analysis 

software, and the supporting information technology infrastructure that will enable a 

collaborative approach to development of predictive models of combustion. This information 

would be warehoused in a comprehensive repository containing all data relevant to modeling 

combustion processes. Development of this library is a community project involving submission 

and evaluation of the relevant data, often presented in the form of a “model” describing a 

particular combustion scenario. Evaluation at this stage is concerned with the data required for 

quantitatively describing the chemical reactions within the model and a measure of the 

uncertainty of the data. In addition, the evaluation will seek to discern a clear documentation as 

to the sources of the data and associated uncertainties; this documentation is often termed the 

traceability or pedigree of the data. 

David M. Golden (Stanford University) presented the talk entitled "Evaluating and Codifying 

Data for Engineering Applications: Atmospheric Chemistry and Combustion." He summarized 

his experiences with multi-institutional collaborations that generated the NASA Chemical 
 20

Kinetics and Photochemical Database for Stratospheric Modeling23 and produced the GRI-Mech 

database, which is the optimized detailed chemical kinetic model that represents natural gas 

flames and ignition during simulations. He characterized the former as a good 19th century-like 

effort towards database development and the latter as a good 20th century-like effort. 

Encouraged by the current advanced state-of-the-art of measurement, computational, and 

information technologies, he called for a 21st century approach to chemical kinetic model 

database development. Continued use of 20th century-like paradigms would be very ineffective, 

given the complexities of the problems that need to be addressed today. 

He emphasized that kinetics data evaluation is a hard and tedious job that can only be 

successfully carried out by expert practitioners in the field. At the present time good 

measurements remain the basis for all evaluations. Theory is playing an increasingly important 

role. Currently, this involves the extension of the measurements to ranges that are not covered by 

the measurements and to set limits on possible rate constants and expressions. 

William H. Green (Massachusetts Institute of Technology) presented a talk entitled "The 

Future of our Field: Predictive Chemical Kinetics." He first noted that a great many chemical 

processes of importance to industry and society, as wide-ranging as combustion, soot formation, 

kerogen maturation, and consumer product aging, proceed via complex sets of reaction 

pathways. The ultimate goal of chemical kinetic modeling for these systems must be to make 

predictions that can guide process design, business, and policy decisions. That goal demands 

that we be able to i) predict the vast array of needed thermochemical and rate parameters, since 

these cannot all be taken from literature data; ii) build models that contain the correct chemistry 

for the conditions of interest; iii) solve the large kinetic models we build to address concrete, 

useful questions; and iv) develop, as a community, standards for the interchange and evaluation 

of data, standard software tools for using and manipulating chemical kinetic models, and 

institutional incentives that will promote collaboration. 

Green gave examples of how to address the first three challenges, but stressed that much more 

work is needed for the fourth, including the formulation of roadmap by the community, and the 

collective development of data standards and tools. 

Larry Rahn (Sandia National Laboratories) presented a talk entitled "Enabling Collaborative 

Science for Real Fuels Combustion." He gave a report of the present status of the Collaboratory 

for Multi-Scale Chemical Science (CMCS). 

Attacking the problem of real fuels combustion requires a multi-scale approach. Multi-scale in 

this context refers to the fact that information from physical scales ranging from the atomistic 

level up to large-scale reaction processes are required to fully address the problem. It is difficult 

to deal with multi-scale information due to the difficulty of propagating the data pedigree 

(including uncertainty, methods, data dependencies, etc.) across scales and the fact that 

annotation and validation of data often occurs after publication of the data. Additional barriers 

 

23 W. B. DeMore, S. P. Sander, D. M. Golden, R. F. Hampson, R. E. Huie, M. J. Kurylo, C. J. Howard, A. R. 

Ravishankara, C. J. Kolb, and M. J. Molina, Chemical Kinetic and Photochemical Data for Use in Stratospheric 

Modeling: Evaluation No. 12 of the NASA Panel for Data Evaluation, JPL Publication 97-4 (April, 1997).
 21

arise, due to the time involved in traditional means of scientific publication, incompatible and 

undocumented data formats, geographic distribution of researchers, and the multi-disciplinary 

nature of collaborators. These difficulties tend to hinder progress. 

CMCS will enhance chemical science research by breaking down the barriers to rapid sharing of 

validated information and by opening new paradigms for multi-scale science. In the longer term, 

new forms of collaborative data sharing and pedigree annotation that complement scientific peer 

review and publication will be created. The CMCS will also enable the creation of radically new 

types of collaborative multi-disciplinary chemical science projects and dramatically increase 

accessibility of state-of-the-art research studies to industry and the public. 

The objectives of the CMCS project are to build an adaptive informatics infrastructure that 

facilitates multi-scale science ventures, to pilot a project within the combustion research 

community, to demonstrate the power of adaptive infrastructure to existing and new areas, to 

gain adoption and continued support via community participation, to document success, and to 

map a continuation path. Current capabilities of the CMCS infrastructure include data sharing, 

collaboration, data and metadata management, annotation, translation, visualization, notification, 

searching and security. 

III. Breakout Session Reports 

On the afternoon of the second day, each participant selected to participate in one (or more) of 

five topical focus sessions: Reference Fuels, Surrogate Fuel Selection, Essential Databases, 

Experimental Validation Data Sets, and Creation of a Roadmap for Combustion Science. Each 

breakout group has formulated recommendations designed to advance combustion science 

though community improvements within the focus topic. 

A. Reference Fuels 

Reporter: Tim Edwards (WPAFB).

Participants: William L. Brown (Caterpillar); Frederick L. Dryer (Princeton U.), briefly; 

Kenneth Erdman (Caterpillar); Daniel Friend (NIST); Jeffrey Manion (NIST); Christopher 

Montgomery (Reaction Engineering); Adel Sarofim (Reaction Engineering & U. Utah). 

This section summarizes discussions of the above group regarding the scientific and engineering 

community needs for databases related to reference fuels. The conclusions of this breakout group 

were presented to the full workshop attendance. 

Reference fuels are used by industry to assess engine-operating parameters, both for design 

purposes and for demonstration of performance related to regulatory requirements. Reference 

fuels may be specified by national [e.g., the U.S. Environmental Protection Agency (EPA)] or 

state regulating agencies [e.g., the California Air Resources Board (CARB)]. Additional agencies 

and specifications are involved for international regulations and vary by region. Regardless of 
 22

regulatory specifications, reference fuels are often needed in very large quantities, making it 

impractical to replace them with pure component mixtures. 

For the foreseeable future, reference fuels will always be needed at some stage in the engine 

design and testing process. However, for purposes of computer simulations and lab-scale device 

testing, it may be possible to develop surrogate fuels that mimic the important characteristics of 

the reference fuels. If successful, this could significantly reduce some of the current needs for 

expensive large-scale testing. 

Various types of information related to reference fuels would be a useful resource to the 

combustion community. This would include information not only on the specific reference fuels 

themselves, but also, for comparison, on real fuels (i.e., commercial products) and some 

commercial hydrocarbons solvents (used as fuels in certain tests). Some of the suggested 

resource data to be made available are summarized below. 

Fuels and Fuel Substitutes Pertinent to Database:

1) Real fuels. 

a) Commercial gasoline fuels from major refiners. 

b) Commercial diesel fuels from major refiners. 

c) Civilian jet fuels: Jet A, Jet A1, Jet B 

d) Military jet fuels: JP-4, JP-5, JP-7, JP-8 (Jet Propellants), RP-1 (Rocket 

Propellant-1 or "rocket kerosene") 

2) Reference fuels. 

a) Diesel: EPA F173 certification fuel. This is a full-boiling, tight specification 

diesel fuel. Note it will change to lower sulfur version in 2007. 

b) Gasoline: to be determined. 

c) Jet fuel: There is presently no generally-accepted reference jet fuel. The Society 

of Automotive Engineers (SAE) has defined a "Jet Reference Fluid" (JRF) that is 

used to evaluate fuel tank sealants. The current composition (SAE AMS 2629B) 

is 28 % toluene, 34 % cyclohexane, and 38 % iso-octane, with t-dibutyl disulfide 

and t-butyl mercaptan added to achieve 0.42 wt % sulfur and 0.005 wt % 

mercaptan sulfur, respectively. The composition is in the process of being updated 

to be more reflective of kerosene jet fuels. 

3) Industrial reference solvents. Industrial solvents are relatively cheap hydrocarbon 

fractions, simpler than real fuels. They include aliphatics, olefins, and aromatics and have 

potential use as test fuels or in test fuel mixtures. A relevant, but incomplete listing is 

given below (all are products of Exxon Mobil Corp. Chemical). 

a) Aliphatics: Norpar, Isopar, Exxsol (all have various grades) 

b) Aromatics: Aromatic 100, Aromatic 150, Aromatic 200 

c) Olefinic: Nonenes, Tetramer K, Tetramer L, Tetramer M 

4) Specific surrogate mixtures: as they are developed. Some preliminary suggestions are 

given later. 
 23

Properties of Interest: A preliminary list of properties defining the important characteristics of 

reference fuels is given below. The possibly incomplete list is intended to be inclusive – that is, 

not all properties will necessarily be needed for all purposes or for all reference fuels or fuel 

substitutes. 

1) Physical and Chemical properties 

a) Chemical composition and range of variation thereof 

b) Cetane number/Octane number 

c) H/C ratio (or heat of combustion) 

d) Chemical class breakdown (paraffins, aromatics, etc.) 

e) Volatility, boiling range, molecular weight 

f) Spray-related properties (viscosity, surface tension) + density 

g) Low temperature kinetics for HCCI (i.e. "cool flames" region) 

2) Other important characteristics: 

a) Cost 

b) Availability/storage life 

Potential Surrogates for Reference Fuels: The following lists initial suggestions by breakout 

session participants of surrogate mixtures that may be shown to mimic reference fuels. 

1) Diesel Fuel (William L. Brown) 

a) Approximately 70 % aliphatics. A mixture of cetane and hexamethyl nonane to 

match the Cetane number. 

b) Approximately 30 % aromatics. Initial suggestion is to use α-methylnaphthalene 

as the single surrogate for aromatics. Based on the most prevalent aromatic 

species in diesel fuels additional possible components are biphenyl, naphthalene, 

and diethylbenzenes. 

2) Jet Fuel: 

a) Violi – two mixtures consisting of different compositions of isooctane/methylcyclohexane/ 

meta-xylene/dodecane/tetralin/tetradecane/decane/toluene. 

b) Dryer (based on available chemical kinetic models) – A mixture of 

n-heptane/iso-octane/toluene/naphthalene/methylcyclohexane 

3) Gasoline: 

 a) Cernansky: A mixture of iso-octane/n-heptane/1-pentene/toluene. 

Target Applications: In general it was felt that any central data center for the community should 

also include discussion of and links to target applications of the data. 
 24

B. Surrogate Fuel Selection 

Reporter: Frederick L. Dryer (Princeton U.).

Participants: Thomas Allison (NIST); David Lenhert (Drexel U.); Charles K. 

Westbrook (LLNL). 

This document summarizes the presentation to the full workshop attendance, which reports the 

breakout session discussions regarding the selection of surrogate fuel candidates for emulating 

gasoline, diesel, and JP-8 conventional fuels. Of particular interest throughout the workshop was 

the recent paper of Violi et al.24 in which the development of a surrogate for JP-8 was described. 

The basic procedural strategy used for JP-8 development involved the following issues, with the 

specific constraints: 

 

1. Feasibility – Candidates in the formula must have known detailed kinetic mechanisms. 

2. Simplicity – Initially limited for computational capabilities to normal paraffins with less 

than 12 carbons, monocyclic paraffins with less than 8 carbons, and simple aromatics 

such as benzene, alkyl-benzenes, and naphthalene. 

3. Similarity – The surrogate is required to match practical fuels on both physical and 

chemical properties: 

a. Volatility – boiling range and flash point; 

b. Sooting Tendency – smoking point and luminous number; 

c. Gross Combustion Property Similarity – heat of combustion, flammability limits, 

and laminar premixed flame mass burning rate 

4. Cost 

The specific issues itemized under each of the listed categories are those utilized by Violi et al., 

and generalization to other fuels require some re-working perhaps of the specific itemizations, 

particularly under Item 3. For example, Item 3a might use 10 %, 50 %, and 90 % volatility 

issues in characterizing a gasoline surrogate mixture "boiling range" rather than a more detailed 

distillation curve. Similarly, gasoline surrogate octane characteristics, and cetane diesel 

surrogate characteristics need to be included in Item 3c in these respective cases. Following the 

discussions of this workshop, there may also be a need for an Item 3d to include similarity issues 

and conventional fuel responses to additives used in commercial products. Finally, smoke point 

might also be replaced by other sooting characterizations in Item 3b, derived from other 

standardized ASTM test procedures as well as more fundamental soot characterization methods. 

As further elaborated by Prof. Sarofim in his workshop discussions, the cost of pure surrogate 

species candidates can become prohibitive in terms of large scale testing, and so surrogate 

species must be chosen with an eye to both fundamental and prototype testing characterization 

against practical fuels 

For the short term, the feasibility and simplicity issues relate to the presently available 

mechanistic information upon which to build more robust models for each candidate and their 

mixtures. Considerations should include not only modeling elements (i.e., the mechanistic 

 

24 A. Violi, S. Yan, E.G. Eddings, F. Sarofim, S. Granata, T. Faravelli, E. Ranzi, Experimental Formulation and 

Kinetic Model for JP-8 Surrogate Mixtures, Combustion Science And Technology 174, 399-417 (2002). 
 25

knowledge base and the thermochemical and elementary rate parameter base) but also the 

existing experimental database upon which to validate component and mixture physical and 

chemical kinetic behavior. These matters are sometimes related to the properties of the actual 

fuel, but may also relate to standard reference mixtures used to characterize conventional fuel 

behavior. For example, as mentioned by Pitz during the presentations, real gasoline does not 

contain n-heptane, and therefore at first appearance one might not consider it as one of the 

surrogate components for a gasoline surrogate. However, as it is one of the two species used in 

defining the octane reference scale (n-heptane and iso-octane) and as a considerable 

experimental database exists for its combustion and physical properties as well as for its 

thermochemical and kinetic parameters, it appears that n-heptane should be included as a 

surrogate fuel candidate. 

 

A number of experimental/modeling studies have utilized n-heptane as a fuel to emulate diesel 

and gas turbine fuel combustion behavior, but the lubricity of n-heptane is insufficient for more 

practically oriented experimental characterizations in, for example, diesel engines. Normal 

decane and n-dodecane both appear as reasonable species on this basis; with more mechanistic 

studies presently emerging using both of these components. Neither of these larger carbon 

number normal paraffins have experimental or modeling databases of similar size to those 

available for the smaller normal and branched paraffins. 

Cetane (n-hexadecane) is a normal paraffin utilized in the cetane reference fuel scale for diesel 

applications, but this species has received very little attention kinetically. It is also worth 

including it as a surrogate fuel species candidate. 

Olefinic species have become more common in processed fuel organic compositions over the 

past decade as refining practices have progressed. Better matching some of the organic 

characteristics of conventional fuels may include a surrogate olefinic component, for example, in 

gasoline surrogate mixtures. Fewer mechanistic and experimental studies of olefinic species 

have been published in comparison to those on alkanes. As an example, however, Drexel 

University (Cernansky and co-workers) presented research that utilized 1-pentene as an olefinic 

component in developing a gasoline surrogate blend of reference components, toluene, and 

1-pentene that would match low temperature and negative temperature coefficient kinetic 

behavior of gasoline. Sufficient small-fragment kinetics information exists for those species 

expected in 1-pentene oxidation. Therefore, the mechanistic and fundamental parameter 

specifications for its oxidation would be straightforward. 

Whereas Violi et al. considered only normal paraffins in representing JP-8, the composition of 

surrogate gasoline mixtures must also include branched paraffins. Iso-octane, the other octane 

reference fuel component, may serve as the representative for this class of compounds. 

Additionally, Westbrook and co-workers have recently considered the varied combustion and 

kinetic behavior of isomers of n-heptane. These species are also reasonable candidates for 

investigating branching effects in gasoline surrogate mixtures. This research shows that these 

species can be used for building a large number of surrogate mixture characteristics that involve 

octane-blending effects and fuel characteristics related to disparate Research and Motor Octane. 

Aromatic species must necessarily be included in surrogate candidates to represent the aromatic 
 26

character effects on auto ignition and, especially, sooting behavior. By regulation, benzene is not 

present in significant quantities in raw conventional fuels, but benzene and phenyl radical 

kinetics need to be considered because benzene and phenyl radicals are formed by various 

kinetic paths in the oxidation of both other aromatic components and non- aromatic components. 

Clearly toluene should be included as a surrogate in developing gasoline surrogate fuels, as this 

species is a very significant component in gasoline and a substantial (but incomplete) 

mechanistic database presently exists. Di-methylated single ring aromatics (xylenes) are not 

present in large quantities in conventional fuels, and it appears from existing experimental 

observations that the emission of these hydrocarbon species is primarily from raw fuel 

component emission, not in situ formation during combustion. Consideration of these 

compounds is likely unnecessary. 

 

In the case of diesel and JP-8 surrogate species candidates, larger carbon number species and at 

least double-ring aromatics appear to be necessary surrogate components, particularly in 

matching volatility and sooting properties. Cetane (n-hexadecane), methyl cyclohexane, and 

1-methyl naphthalene should likely all be selected as surrogate component candidates, as they 

are again species utilized in formulating cetane reference fuel mixtures. Violi et al. also 

considered tetralin as a surrogate candidate. Finally, Dryer noted in his workshop presentation 

that in a combination of engine and fundamental studies on diesel combustion and the effects of 

common cetane improvers, a mixture of n-hexadecane, decahydronaphthalene (decalin), and 

1-methylnaphthalene was shown to closely emulate the behavior of full blend diesel fuel under 

the same test conditions. It appears that decalin may also be an interesting surrogate candidate to 

consider. 

Summarizing, a first selection of surrogate candidates for covering all of the above classes of 

conventional fuels should include olefinic species, e.g., 1-pentene; normal paraffins; e.g., 

n-heptane, decane, dodecane, n-hexadecane; iso-paraffins, e.g., heptane isomers, iso-octane; 

single ring aromatics, e.g., toluene; multi-ring aromatics, e.g., 1-methyl naphthalene, tetralin, 

and decalin; and cyclo-paraffins, e.g., methyl cyclo hexane. 

In the short term, developing chemical kinetic models on similarity and grouping methods such 

as those used in Violi et al. is a methodology to circumvent the present lack of mechanistic 

information and fundamental thermochemical and chemical kinetic parameters. Comprehensive, 

hierarchical mechanism development combined with these methods can produce initial chemical 

kinetic models. Automatic mechanism generation with accompanying estimation methods for 

the needed thermochemical and rate data can also produce the needed starting mechanism. In 

each case, it is beneficial to minimize the chemical kinetic model through detailed reduction 

methods applied over the range of parameters and conditions for which the model prediction will 

be constrained by comparison with experimental targets. Minimization is essential to achieving 

a computational efficiency required for parametric studies and the application of formal 

numerical analyses using sensitivity studies and other methods to study and optimize model 

predictive behavior. Additionally, reduction methodologies will be required to produce models 

that can be utilized in multidimensional applications. 

In all of the above, experimental observations are required to validate the model behavior and to 

assist in identifying the relative significance of individual surrogate species upon various 
 27

combustion issues. Westbrook favored developing chemical kinetic models and performing 

analyses principally using predictions of experimental targets produced using prototype energy 

conversion situations, such as engines, model combustors, and rapid compression machines. 

While not discounting the utility of such targets, Dryer suggested that that model comparisons at 

this level of complexity can fail to decouple the uncertainties in the respective sub-models such 

that the source(s) of inadequacy in the various sub-models can be identified and mitigated. 

Chemical kinetic sub-model development and validation can be significantly improved by using 

experimental targets that essentially do not involve transport effects such as shock tubes, flow 

reactors, and stirred reactors, and fundamental configurations that are strongly affected by 

transport such as laminar premixed flames (flat flame burner studies, flame velocity 

determination), and laminar diffusion flame (opposed jet, stagnation, and isolated droplet 

configurations, including those that characterize extinction). The database of fundamental 

experimental targets should include results on individual surrogate components, surrogate 

mixtures, and conventional fuels. Experimental uncertainties of targets need to be carefully 

assessed and defined. 

C. Essential Databases 

Reporter: Jeffrey Hudgens (NIST).

Participants: Timothy Barckholtz (Exxon Mobil Corp.); Donald Burgess (NIST); Robert Huie 

(NIST); M. C. Lin (Emory U.); William J. Pitz (LLNL); Graham Westmacott (Reaction Design, 

Inc.). 

This section summarizes the discussions among the above regarding the scientific and 

engineering community needs for databases that will enable accurate modeling of combustion 

processes involving real fuels, i.e., gasoline, diesel, and aviation fuels. The conclusions of this 

breakout group were presented to the full workshop. 

 

The goal of the combustion community is to develop computational models that can simulate the 

performance and emissions of engines and burners. Since state-of-the-art chemical kinetic 

models are constructed from reaction sets, elementary rate coefficients, and thermochemical 

data, the group recommended that effective service to the combustion community would be 

accomplished by a unified website containing the following databases: 

1. Thermochemical property data ( o ∆f H , o S , o Cp , etc.) for fuel components and reaction 

intermediates. 

a) Extensive compilation of all available data. 

b) Critically evaluated (recommended) data.

2. Elementary rate coefficients (k) of reactions relevant to combustion. 

a) Extensive compilation of all available data.

b) Critically evaluated (recommended) data.

3. Chemical Kinetic Models used within the community for combustion simulations. 
 28

a) Tools enabling comparisons among the chemical kinetic models. 

b) Translators that relate the acronym labels within each database record (which, 

itself, contains a chemical kinetic model) to the chemical structure of each 

species. 

In a computer simulation program the complete reaction set is the algebraic list of all stepwise 

chemical changes that may occur during a combustion process. The elementary rate coefficients 

are numbers describing the rates with which each reaction step proceeds. The thermochemical 

data are numbers associated with each species that are used to compute the energy release by 

reaction steps. Thermochemical data also assure thermodynamic consistency between forward 

and reverse reaction rate coefficients in thermalized systems and facilitate estimations of rate 

coefficients for which direct measurements are unavailable. 

Currently, NIST provides substantial service to the combustion community by publishing items 

1a and 2a through the NIST Chemical Kinetic Database25 and the NIST Chemistry WebBook.26

Within these databases each record provides the information needed by the user to trace the 

origin of the data and to evaluate the quality of each number and uncertainty. The breakout group 

emphatically agreed that NIST should continue to maintain these databases and add new data, as 

they become available. 

The group identified a strong need for "critically evaluated" databases of thermochemical 

properties and elementary rate coefficients. The existing evaluated databases addressing 

combustion needs are not continually updated and do not reflect current, accepted "best values." 

A critically evaluated database would span a group of important combustion species. For each 

species a critically evaluated database would list "recommended" numbers found by identifying 

the best data and re-adjusting numbers (within their uncertainties) to optimize agreement among 

the observed and calculated exothermicities and relative reaction rates. Ideally, the existence of 

critically evaluated databases would greatly reduce the extensive effort required of researchers 

when they need to trace and ascertain the quality and uncertainty of rate coefficients and 

thermochemical values. The widely-used NIST databases are compilations, not evaluations, nor 

recommendations. It was suggested that NIST could accelerate the creation of critically 

evaluated databases by organizing committees drawn from the academic and other experts and 

facilitating communication by hosting websites and workshops. This will require the 

development of standardized formats or templates for reporting kinetic and modeling data. 

The breakout group identified a strong need for a compilation of complete and reduced chemical 

kinetic models. No database devoted to chemical kinetic models is available, nor is any 

organization known to be assembling such a database. The need for a chemical kinetic model 

database is driven by the emergence of computational codes that more accurately simulate 

macroscopic flames by accounting for the effects of fluid dynamics and chemical reactions. 

Industry is increasingly adopting these codes to accelerate product development and optimization 

through accurate simulation of macroscopic flame behavior. 

 

25 Chemical Kinetics Database on the Web, NIST, 2000 (http://kinetics.nist.gov). 

26 H.Y. Afeefy, J.F. Liebman, and S.E. Stein, "Neutral Thermochemical Data" in NIST Chemistry WebBook, 

NIST Standard Reference Database Number 69, Eds. P.J. Linstrom and W.G. Mallard, March 2003, National 

Institute of Standards and Technology, Gaithersburg MD, 20899 (http://webbook.nist.gov). 
 29

The breakout group concluded that the creation of a chemical kinetic model database would 

benefit industry through rapid dissemination of improved models. The database would also 

accelerate research directed to model optimization by bringing about standards for nomenclature, 

notation, traceability, and communication. The present absence of such standards and the 

absence of a central data repository prevent facile comparison of models developed by different 

researchers. These absences hamper efforts to determine why two models may predict the same 

results under one set of conditions yet diverge as conditions change. Such comparisons are 

essential for identifying the absence of important elementary reactions and presence of 

inaccurate rate coefficients. It was suggested that NIST create this web-based database and host a 

workshop that will discuss and define 1) the database organization, 2) flexible reporting 

protocols that can accommodate the dissonant nomenclature in the community, 3) translation 

tools for relating acronyms to chemical structures, and 4) software tools that enable visualization 

of the differences among chemical kinetic models. 

D. Experimental Validation Data Sets 

Reporter: Nicholas Cernansky (Drexel U.).

Participants: Thomas Avedesian (Cornell U.); Kenneth Brezinsky (U. Illinois, Chicago); John 

Farrell (Exxon Mobil); David Leahy (Sandia); Balu Sekar (AFRL/PRTC); Mitchell D. Smooke 

(Yale U.). 

The group not only looked at the specific issues assigned to the group, but it also looked at the 

big picture, as seen in the overall context of the workshop. A few key points and positions 

emerged from the discussions. 

1. The underlying and driving force behind this workshop on Real Fuels and Simulation 

of Realistic Combustion Systems is the overarching need for energy independence and a 

cleaner environment. Members of the breakout group indicated that they would be 

willing to do their part in this pursuit and felt that this enthusiasm can be used to generate 

support for the activity. 

2. There is a critical need for reference fuels (gasoline, diesel, gas turbine) and for 

appropriate surrogates (which may be application specific) that can be used for 

development and validation purposes. Addressing this need will require the active 

involvement and support of government agencies—particularly from the Department of 

Defense (DOD) and the Department of Energy (DOE)—to develop such fuels and 

surrogates. 

3. DOD and DOE should begin a program to support development/creation of appropriate 

reference fuels and surrogates. NIST should spearhead this effort and serve as a central 

repository for the associated data and information, including kinetic rates, 

thermochemistry, transport phenomena, chemical kinetic models, and experimental 

validations. 
 30

4. The community knows how to evaluate fuel properties and to generate the data 

necessary for validation of surrogate mixtures with reference to these fuels. Depending 

on the specific questions/hypotheses being posed, a sequence of highly directed 

experiments can be conducted to provide the necessary validation data. 

5. There is a suite of canonical experiments (well developed and used for many years) 

that can be employed to address issues associated with the behavior of realistic 

combustion systems and their models. Experiments using shock tubes, flow reactors, 

premixed flames, counter flow flames, and droplet/spray systems (to name just a few) can 

be conducted over appropriate ranges of T, P, equivalence ratio, etc. (even approaching 

practical conditions) to generate data germane to the modeling and prediction of autoignition, flame behavior, ignition/extinction, emissions (e.g., NOx & soot), and other 

phenomena in realistic combustion systems. 

E. Creation of a Roadmap for Combustion Science

Reporter: Wing Tsang (NIST). 

Participants: Meredith B. Colket (United Technologies Res. Ctr.), William H. Green (MIT), 

William Kirchhoff (DOE); Thomas Sloane (GM Res. & Dev.), M. C. Lin (Emory U.) 

The goal of the breakout session was to help NIST devise a roadmap for building databases and 

chemical kinetic models for the combustion of real fuels, so that they may be used for CFD 

modeling of realistic systems. The target was transportation fuels. The elements for such an 

effort were outlined with general agreement that this was a desirable and achievable goal. There 

was general agreement that this must include the construction of detailed chemical kinetics 

models for transportation fuels that will permit the simulation of the combustion of gasoline, 

aircraft and transportation fuels. These models should be capable of reproducing chemical 

kinetics related issues bearing on operation, performance and emissions. It should be reducible 

for use in CFD codes and a target date of 2007 was suggested when the work will become 

available for general use. 

A listing of specific tasks was given. These include the selection of surrogate fuels and the range 

of composition to be used and the particular combustion kinetics features that models should 

seek to reproduce. The nature of the data to be generated in the context of surrogates and actual 

fuels (reference fuels) must be defined. The effort should include programs for fundamental 

measurements, theoretical modeling, validation, informatics, tool development and chemical 

kinetic model reduction. Although it was agreed the that a NIST derived database will be a 

valuable contribution to combustion technology, the full benefits of the technology can only be 

achieved in the context of a combustion kinetics information center to serve as a clearing house 

for all aspects of work tied to the use of fundamental physico-chemical data in combustion 

applications. 

It is proposed that the various components for the information center have designated team 
 31

leaders and that individual research plans and schedules should be identified and formulated. 

NIST, drawing upon the expertise of the community should articulate and communicate a high 

level plan. There is a need to sort out the mechanisms and interactions for the central clearing 

house and NIST/CMCS/PrIMe. 

It also became apparent that the combustion community was badly in need of a roadmap in a 

more general sense. In particular there is the need to identify and agree on longer-term objectives 

and the strategies to focus the community activities in this direction. It was agreed that this was a 

remarkable deficiency of the combustion community since practically all successful larger scale 

projects have well defined goals and roadmaps on how to get there. Examples cited include the 

human genome project, the astrophysics community, the stratospheric ozone program and the 

high-energy physics community. These plans should be carried out in the context of no extra 

funding. It is an activity that should draw upon the expertise of the entire combustion 

community. As with the case for the NIST database efforts, a key motivation is the development 

of CFD codes that have the potential of projecting laboratory results directly into the real world. 

The HCCI engine was cited as an example where a combination of laboratory experiments and 

CFD simulations may lead to large savings in energy without offsetting increases in undesirable 

emissions. 
 32

GLOSSARY 

The following glossary contains definitions of terms as used in this document. Where possible, 

the International Union of Pure and Applied Chemistry (IUPAC) definition is used.27

Emissions: 

• NOx – A short-hand term used to denote collectively all oxides of nitrogen. 

• Polycyclic aromatic hydrocarbon or PAH – Large molecular weight hydrocarbon molecules, 

composed mainly of carbon and hydrogen, which have chemical structures containing many 

aromatic and non-aromatic carbon ring groups. 

• Particulate Matter or PM (both terms are used in atmospheric chemistry) – A general term used 

to describe airborne solid or liquid particles of all sizes. 

• PM10 – An acronym for particles ≤ 10 μm (10 microns) diameter. The National Ambient Air 

Quality Standards (NAAQS) for Particulate Matter (PM) regulation14 sets the ambient air PM10

concentration to less than 150 μg/m3

 over a 24 hour period and an annual average of 50 μg/m3

annual average. 

• PM2.5 – An acronym for particles ≤ 2.5 μm (2.5 microns) diameter. The National Ambient Air 

Quality Standards (NAAQS) for Particulate Matter (PM) regulation14 sets the ambient air PM10

concentration to less than 65 μg/m3

 over a 24 hour period and an annual average of 15 μg/m3

annual average. 

• Soot – A generic term for particulate matter composed mainly of carbon. Current data indicate 

that soot is formed from reactions involving PAH species. 

• SOx – A short-hand term used to denote collectively all oxides of sulfur including SO2. 

Fuels: 

• Cetane Number – A value derived from the measured ignition delay observed for a diesel fuel. 

This is the time period between the start of injection and start of combustion (ignition) of the fuel. 

In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than 

lower cetane fuels. (Cetane number is often mistaken as a measure of fuel quality.) 

• Octane Number – A value used to indicate the resistance of a motor fuel to knock. Octane 

numbers are based on a scale on which isooctane is 100 (minimal knock) and heptane is 0 (bad 

knock). 

Model:

• Simulation Model – A collection of algebraic equations and associated coefficients that 

describes the transport properties of the chemical species, the fluid dynamic boundary conditions, 

the system geometry, and the chemical kinetic model. 

• Chemical Kinetic Model – A collection of symbolic equations and numbers comprising the 

reaction set, the associated rate coefficients, and the thermochemical properties of species. 

• Reduced Chemical Kinetic Model – A collection of symbolic equations and numbers 

comprising the reduced reaction set, the associated rate coefficients, and the thermochemical 

properties of species. The reduced chemical kinetic model may contain lumped reactions and 

lumped rate coefficients. 

 

27 International Union of Pure and Applied Chemistry, IUPAC Compendium of Chemical Terminology, Oct 2003 

(http://www.iupac.org/publications/compendium/index.html). 
 33

Organizations: 

• CMCS – Collaboratory for Multi-Scale Chemical Science. 

• DOD – Department of Defense. 

• DOE – Department of Energy. 

• NIST – National Institute of Standards and Technology. 

Rate Coefficient:

• Elementary Rate Coefficient – A number describing the rate at which an elementary reaction 

step proceeds. 

• Lumped Rate Coefficient – A number describing the rate at which a lumped reaction proceeds. 

Reaction: 

• Chemical Reaction – A chemical reaction is a process that results in the interconversion of 

chemical species. Chemical reactions may be elementary reactions or stepwise reactions. 

• Elementary Reaction – An algebraic representation of a chemical transformation for which no 

reaction intermediates have been detected or need to be postulated in order to describe the 

chemical reaction on a molecular scale. An elementary reaction is assumed to occur in a single 

step and to pass through (at most) a single transition state. 

• Isomerization Reaction – A chemical reaction, the principal product of which is isomeric with 

the principal reactant. Isomeric species are molecular entities that have the same stoichiometric 

molecular formula, but differ with respect to the connectivities of the atoms, their respective bond 

orders, or the spatial arrangement of the atoms. 

• Lumped Reaction – A collection of elementary reactions expressed as an “equivalent” apparent 

single-step reaction. A lumped reaction may be a stepwise reaction, involving a consecutive set 

of elementary reactions, the simplest example being A → I → B, where I is a steady state 

intermediate. A lumped reaction may also be a set of related, but dissimilar reactions, operating 

as alternative or parallel pathways, or A → {In} → B, where {In} represents the set of parallel 

pathways. A lumped reaction may also be a set of similar reactions, operating collectively, on 

similar molecular species, or {A} → {I} → {B} where {A}, {I}, and {B} are sets of similar 

reactants, intermediates, and products, respectively. 

• Reaction Intermediate – A reaction intermediate is a molecular entity with a lifetime 

appreciably longer than a molecular vibration (corresponding to a local potential energy 

minimum of depth greater than RT) that is formed from the reactants and reacts further to give 

the products of a chemical reaction. 

• Transition State – A transition state is a state of more positive molar Gibbs energy between the 

reactants and the products through which an assembly of atoms must pass on going from 

reactants to products in either direction. 

Reaction Set: 

• Complete Reaction Set (or Reaction Sequence) – A list of elementary reactions comprising all 

conceivable combinations of reactants and products with no judgment of their importance. This is 

a theoretical construct that is probably never known for any complex system. 

• Initial Reaction Set – An algebraic list of stepwise chemical changes believed important to a 

combustion process in the absence validation or testing. 

• Reduced Reaction Set – An abridged algebraic list of stepwise chemical changes abstracted 

from the initial or complete reaction set that attempts to contain the minimal list of reactions 

required to capture the relevant chemistry for a particular problem and set of conditions. A 

reduced reaction set may contain lumped reactions; hence, the list of rate coefficients may include 

lumped rate coefficients. 
 34

SPONSORSHIP 

The Workshop on Combustion Simulation Databases for Real Transportation Fuels was 

sponsored by the National Institute of Standards and Technology and convened at its 

Gaithersburg, MD campus on September 4-5, 2003. The workshop was organized in response to 

the recognized overwhelming importance of energy production to United States commerce. 

NIST resides within the U.S. Department of Commerce and has non-regulatory roles to provide 

fundamental technical measurements, standards, and expertise in support of the U.S. economy. 

Services include the provision of definitive measurement traceability mechanisms (standard 

reference materials, standard reference data, and calibrations), fundamental chemical kinetic 

data, and thermodynamic measurement data. The services performed by NIST are integral to the 

sound science needed by the Nation to effectively engage in combustion and atmospheric quality 

issues in a way that assures that domestic industry remains competitive in the international 

market. 

This report was assembled by the workshop Chairman, Dr. Wing Tsang, and by members of the 

Real Fuel Project Team; Drs. Thomas C. Allison; Donald R. Burgess, Jr.; Jeffrey W. Hudgens; 

Jeffrey A. Manion; and David M. Matheu from their conference notes, from the speakers’ 

presentation materials, and from the breakout session summaries written by the indicated 

reporters. References to this document should cite its publication number, NISTIR 7155.
 35

ATTENDEES 

Thomas C. Allison, NIST 

thomas.allison@nist.gov 

C. T. Avedisian, Cornell U. 

ctaz@cornell.edu 

Timothy A. Barckholtz, Exxon Mobil 

tim.barckholtz@Exxon Mobil Corp..com 

Anuj Bhargava, Pratt & Whitney 

anuj.bhargava@pw.utc.com 

Kenneth Brezinsky, U. Ill., Chicago 

kenbrez@uic.edu 

William L. Brown, Caterpillar 

Brown_William_L@cat.com 

Donald Burgess, NIST 

dburgess@nist.gov 

Nicholas Cernansky, Drexel U. 

cernansk@coe.drexel.edu 

Meredith B. Colket, United Technologies 

Res. Ctr. 

colketmb@utrc.utc.com 

Anthony M. Dean, Colorado School 

 of Mines 

amdean@mines.edu 

Frederick L. Dryer, Princeton U. 

fldryer@princeton.edu 

Tim Edwards, AFRL 

james.edwards@wpafb.af.mil 

Kenneth Erdman, Caterpillar 

Erdman_Kenneth_D@cat.com 

John Farrell, Exxon Mobil 

john.t.farrell@ExxonMobilCorp.com 

Michael Frenklach, U. California, Berkeley 

myf@me.berkeley.edu 

Daniel Friend, NIST 

daniel.friend@nist.gov 

David M. Golden, Stanford U. 

david.golden@stanford.edu 

Graham Goldin, Fluent Inc. 

gmg@fluent.com 

William H. Green, MIT 

whgreen@mit.edu 

John Hewson, Sandia 

jchewso@sandia.gov 

Jeffrey W. Hudgens, NIST 

hudgens@nist.gov 

Robert E. Huie, NIST 

robert.huie@nist.gov 

Karl Irikura, NIST 

karl.irikura@nist.gov 

Viswanath Katta, Innovative Scientific 

Solutions, Inc. 

vrkatta@erinet.com 

William Kirchhoff, Dept. of Energy 

william.kirchoff@science.doe.gov 

Vadim Knyazev, NIST/CUA 

knyazev@cua.edu 

Chung K. Law, Princeton U. 

cklaw@princeton.edu 

David Leahy, Sandia 

djleahy@sandia.gov 
 36

ATTENDEES -- continued 

David Lenhert, Drexel U. 

dblenhert@drexel.edu 

M. C. Lin, Emory U. 

chemmcl@emory.edu 

Gregory T. Linteris, NIST 

linteris@nist.gov 

Gregory J. McRae, MIT 

McRae@mit.edu 

Jeffrey Manion, NIST 

jeffrey.manion@nist.gov 

David Mann, Army Research Office 

dmann@aro.arl.army.mil 

David Matheu, NIST 

david.matheu@nist.gov 

Christopher Montgomery, REI 

montgomery@reaction-eng.com 

Robert Pawlik, AFRL 

robert.pawlik@wpafb.af.mil 

William J. Pitz, LLNL 

Pitz1@llnl.gov 

Larry Rahn, Sandia National Laboratory 

Combustion Research Facility 

rahn@sandia.gov 

Richard Reich, AFRL 

Richard.Reich@wpafb.af.mil 

Gregory Rosasco, NIST 

gregory.rosasco@nist.gov 

Adel Sarofim, REI/U. Utah 

sarofim@aros.net 

Mary Anne Scott, Department of Energy 

scott@er.doe.gov 

Balu Sekar, AFRL/PRTC 

balu.sekar@wpafb.af.mil 

Robert Shaw, ARO 

shaw@aro.arl.army.mil 

Thomas Sloane, General Motors Research & 

Development 

thompson.m.sloane@gm.com 

Richard N. Smith, NSF 

rnsmith@nsf.gov 

Mitchell D. Smooke, Yale U. 

mitchell.smooke@yale.edu 

Julian Tishkoff, AFOSR 

Julian.Tishkoff@afosr.af.mil 

Wing Tsang, NIST 

wing.tsang@nist.gov 

Frank Tully, Dept. of Energy 

frank.tully@science.doe.gov 

Hai Wang, U. Delaware 

hwang@me.udel.edu 

Charles K. Westbrook, LLNL 

westbrook1@llnl.gov 

Graham Westmacott, Reaction Design, Inc. 

gwestmacott@reactiondesign.com 

Michael R. Zachariah, U. Maryland 

mrz@umd.edu