Swaminathan N., Bray K.N.C. (eds.) Turbulent Premixed Flames

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Preface

Turbulent combustion is rich in physics and is also a socioeconomically important

topic. Much research has been carried out in the past half century, resulting in many

important advances. It is simply impractical to review and discuss all of these studies

and to explain their results in a single book. Many volumes published in the past

reviewed such material, and we draw attention in particular to the two volumes

edited by Paul Libby and Forman Williams, published in 1980 by Springer-Verlag

and in 1994 by Academic Press, covering both non-premixed and premixed turbulent

ﬂames and the book by Norbert Peters published by Cambridge University Press in

2000.

The recent outcry on environmental impacts of anthropogenic sources has re-

sulted in a strong emphasis on alternative means for power generation by use of

wind and solar energies. However, for high-energy density applications such as

transportation, combustion of fossil or alternative fuels will remain indispensable

for many decades to come. Thus more stringent emissions legislation will be intro-

duced and constantly revised in order to curtail the growing impact of combustion

equipment on the environment. Fuel-lean combustion in a premixed or partially

premixed mode is known to be a potential route to control emissions and to improve

efﬁciency in both automobile engines and gas turbines. These two modes of combus-

tion involve a strong coupling among various physical processes; to name a few of

these processes, turbulence, chemical reactions, molecular diffusion, and large- and

small-scale mixing are involved in turbulent lean combustion. Recognising these in-

terplays, Chapter 1 surveys the current modelling approaches for turbulent premixed

ﬂames from a physical perspective. Chapter 2 describes these modelling methods in

some detail. Lean premixed ﬂames are notoriously unstable, and thus any analy-

sis of them would be incomplete without addressing their instabilities. This topic

is covered in Chapter 3. Current practice and challenges of fuel-lean combustion

in practical devices such as internal combustion engines and gas turbines are de-

scribed in Chapter 4, and future technological and scientiﬁc directions are discussed

in Chapter 5.

We aim to provide a simple and clear discussion in terms of physical processes

that can be followed by a graduate student with a good background in ﬂuid mechanics,

and combustion and some knowledge of turbulence modelling, together with some

analytical skills. Many recent references are provided for further reading. We also

x Preface

attempted to make the discussion interesting for readers who are already familiar

with turbulent premixed combustion, to help them to appreciate the complexity of

this subject and the seriousness of the challenge involved in successfully introducing

fuel-lean combustion to practical systems.

We would like to thank all the contributors, without whose dedication and

cooperation it would not have been possible to meet our objectives in this volume.

N. Swaminathan

K. N. C. Bray

Cambridge, UK

March 2011

Contributors

D. Bradley, FRS, FREng, FIMechE, FInstP, is a Research

Professor in the School of Mechanical Engineering at the

University of Leeds, with interests in most aspects of com-

bustion and energy. He was Editor of Combustion and

Flame for 14 years and served as a consultant to sev-

eral energy and engine companies. He has been involved

in investigations of aircraft ﬁres and large explosions.

e-mail: d.Bradley@leeds.ac.uk.

K. N. C. Bray has degrees from Cambridge, Princeton, and

Southampton Universities. He was Professor of Gas Dy-

namics at Southampton and then Hopkinson and Imperial

Chemical Industries Professor of Applied Thermodynam-

ics at Cambridge, where he is now an Emeritus Professor.

His current research interests in combustion include the

various ways in which turbulence interacts with combus-

tion processes. He was Editor of Combustion and Flame

from 1981 to 1986 and was elected to a Fellowship of The

Royal Society in 1991, e-mail: knc.bray@btinternet.com.

N. Chakraborty is a Senior Lecturer in the Department of

Engineering, University of Liverpool. He obtained a Ph.D.

in 2004 from Cambridge University, Engineering Depart-

ment, supported by a Gates Cambridge Scholarship. His re-

search involves modelling of turbulent premixed ﬂames and

localised ignition of turbulent gaseous and droplet-laden

inhomogeneous mixtures by use of direct numerical simu-

lation. He also works on turbulent convective heat transfer

with phase change in applications such as casting, welding,

and laser melting. e-mail: n.chakraborty@liverpool.ac.uk.

xii Contributors

M. Champion is CNRS scientist and works at the Labora-

toire de Combustion et D

eetonique, Poitiers. He obtained

his Ph.D. in 1980. His research interests are all related

to the ﬁelds of ﬂuid mechanics, combustion and turbulent

ﬂows, with a special emphasis on the modelling of t urbu-

lent ﬂames. Since 1981 he has been regularly invited as

a Visiting Professor by the Department of Mechanical and

Aerospace Engineering of the University of California, San

Diego. e-mail: michel.champion@lcd.ensma.fr.

P. Domingo is CNRS scientist at CORIA. She obtained her

Ph.D. from the University of Rouen in 1991 and then joined

Stanford University Aerospace Department as a post-doc.

She has developed fully coupled solvers for plasma ﬂows

and ﬂames to analyze reacting ﬂow physics by using di-

rect numerical simulation and large-eddy simulation. She

also interacts with industry to help in the optimisation of

reliable, fuel-efﬁcient, and environmentally friendly com-

bustion systems. e-mail: domingo@coria.fr.

A. P. Dowling is the Head of Department of Engineering,

University of Cambridge, where she is Professor of Me-

chanical Engineering and Chairman of the University Gas

Turbine Partnership with Rolls-Royce. Her research is pri-

marily in the ﬁelds of combustion, acoustics, and vibration

and is aimed at low-emission combustion and quiet vehi-

cles. She is a Fellow of the Royal Society, Royal Academy of

Engineering, and is a Foreign Member of the U.S. National

Academy of Engineering and of the French Academy of

Sciences. e-mail: apd1@cam.ac.uk.

J. F. Driscoll is a Professor of Aerospace Engineering at the

University of Michigan, where he conducts fundamental

research in the area of premixed turbulent ﬂames as well as

applied research in lean premixed gas turbine combustors

and scramjet devices. He has developed specialised diag-

nostics to image the physics of ﬂame–eddy interactions. He

is a Fellow of the AIAA and is a former editor of Combus-

tion and Flame. e-mail: jamesfd@umich.edu.

Contributors xiii

L. Y. M. Gicquel received his Ph.D. from the State Uni-

versity of New York at Buffalo in 2001. He then joined the

CERFACS computational ﬂuid dynamics team at Toulouse,

France, to become a Senior Researcher, and he contributes

to the development of massively parallel large-eddy simu-

lations and acoustic solvers for industrial applications. His

areas of expertise cover turbulent reacting ﬂows, large-eddy

simulations, direct numerical simulations, two-phase ﬂows,

pollutant emissions, stochastic processes, and combustion

instabilities. e-mail: lgicquel@cerfacs.fr.

S. Hayashi is a Professor in the Science Engineering De-

partment, Hosei University, Japan. He obtained his Ph.D.

in engineering in 1971 from the University of Tokyo and

was involved in research and project management in The

National Aerospace Laboratory and Japan Aerospace Ex-

ploration Agency from 1972 to 2009. His research includes

low-emission gas turbine combustion and laser diagnostics

of sprays. e-mail: hayashi@hosei.ac.jp.

B. Jones is a consultant, specialising in gas turbine com-

bustion, and is a Fellow of the Institute of Mechanical En-

gineering. He worked in this ﬁeld from 1968 to 2003 for

Rolls-Royce plc. From 1990 he was responsible for man-

agement of the design of new aeroengine combustion sys-

tems and their demonstration, and was responsible for the

rapid expansion of participation by Rolls-Royce in collab-

orative combustion research within the EC and in the Far

East. e-mail: bryn.jones@kausis.adsl24.co.uk.

P. Lindstedt received his M. Eng. degree from Chalmers

University in 1981 and his Ph.D. from Imperial College

in 1984 where he was appointed Professor in 1999. He

served as Deputy Editor of Combustion and Flame (2000–

2010) and as Colloquium Co-Chair for the 30th Interna-

tional Combustion Symposium. His research interests are

focussed on the interactions of chemistry with ﬂow, and

he has received the Sugden Award and the Gaydon Prize.

e-mail: p.lindstedt@imperial.ac.uk.

xiv Contributors

Y. Mizobuchi is a Senior Researcher in Aerospace Re-

search and Development Directorate, Japan Aerospace

Exploration Agency. He obtained his Ph.D. in 1995 from

the University of Tokyo. His research interest includes nu-

merical elucidation of turbulent combustion using super-

computer systems. He also engages in research and devel-

opment activities on prediction and control of combustion

instability and environmental acceptability of aerospace

propulsion systems. e-mail: mizo@chofu.jaxa.jp.

A. S. Morgans is a Lecturer in the Department of Aero-

nautics, Imperial College London. She obtained a Ph.D.

in Acoustics from Cambridge University Engineering De-

partment in 2003. She then held a Royal Academy of En-

gineering/EPSRC Fellowship for research into the active

control of combustion instabilities (2004 and 2009) at Cam-

bridge and then at Imperial College. Her research inter-

ests include acoustics, combustion instabilities, and active

control of ﬂows. She was awarded the SET for Britain’s

‘Top Younger Engineer’s Award’ and the Gold Medal in

2004 for her work on controlling combustion instabilities.

e-mail: a.morgans@imperial.ac.uk.

V. Moureau is a CNRS scientist at CORIA. He obtained a

Ph.D. in 2004 from Institut Franc¸ais du P

etrole and Ecole

Centrale Paris. After a two-year post-doctoral fellowship at

Stanford University in the Center for Turbulence Research,

he joined Turbomeca, SAFRAN group, as a combustion

engineer from 2006 to 2008. His research is focussed on

turbulent combustion and spray modelling and on the de-

velopment of YALES2 solver for large-eddy simulations

and direct numerical simulation of turbulent ﬂows in com-

plex geometries. e-mail: vincent.moureau@coria.fr.

A. Mura is a senior scientist working for CNRS, Poitiers,

France. After an academic cursus at the University

of Rouen (INSA), he obtained a Ph.D. from ESM2

(Ecole Centrale Marseille). His teaching activities include

postgraduate level courses and international short lec-

tures. His research is devoted to the analysis of multi-

phase and reactive media with a broad range of tech-

nical issues encountered in practical systems, spanning

from combustion in engines to rocket propulsion. e-mail:

arnaud.mura@lcd.ensma.fr.

Contributors xv

F. Nicoud has been a Professor in the Mathematics De-

partment at the University of Montpellier since 2001. He

teaches applied mathematics and scientiﬁc computing at

the School of Engineering. He gained his Ph.D. in 1993

from Institute National Polytechnique in Toulouse and then

was appointed a Senior Researcher at CERFACS in 1995.

He held a fellowship at Center for Turbulence Research,

Stanford University. His research interests span from ana-

lytical and numerical studies of thermoacoustic instabilities

and combustion noise and wall-modelling issues in complex

turbulent ﬂows to computation of blood ﬂow under physi-

ological conditions. e-mail: franck.nicoud@univ-montp2.fr.

T. J. Poinsot received a Ph.D. in heat transfer from Ecole

Centrale Paris in 1983 and his These d’Etat in combus-

tion in 1987. He is a Research Director at CNRS, Head of

the Computational Fluid Dynamics Group at CERFACS,

Senior Research Fellow at Stanford University, and consul-

tant at Institut Franc¸ais du P

etrole, Air Liquide, Daimler.

He teaches numerical methods and combustion in Ecole

Centrale Paris, ENSEEIHT, ENSICA, Supaero, UPS, Stan-

ford, and VKI. He has authored more than 120 papers in

journals and 200 communications. He has co-authored a

textbook Theoretical and Numerical Combustion with D.

Veynante. He is an associate editor of Combustion and

Flame. e-mail: Thierry.Poinsot@cerfacs.fr.

N. Swaminathan is a University Lecturer in the Cambridge

University Engineering Department and a Fellow and Di-

rector of Studies at Robinson College. He gained a Ph.D.

in 1994 from the University of Colorado, Boulder, and his

research interest includes modelling and simulations of tur-

bulent combustion. His professional experiences span from

academia to industries. He has served on the editorial board

of the Open Fuels and Energy Science journal since 2009

and he has been a member of EPSRC (Engineering and

Physical Sciences Research Council) College, UK, since

2006; e-mail: ns341@cam.ac.uk.

A. M. K. P. Taylor graduated in 1975 and obtained his Ph.D.

in 1981 from Imperial College. After brief visits to the Uni-

versity of Karlsruhe (as a DAAD scholar) and the NASA

Lewis Research Center, he was a Royal Society Univer-

sity Research Fellow from 1985 to 1990, subsequently be-

ing appointed Lecturer in the Department of Mechanical

Engineering. He was promoted to a Professor of Fluid Me-

chanics in the same department in 1999. His interest in basic

research is in the ﬁelds of two-phase ﬂow and combustion,

xvi Contributors

combined with the development of optical instruments for

these two areas. His applied research includes spray drying

and combustion in gas turbines and, of course, internal

combustion engines. e-mail: a.m.taylor@imperial.ac.uk.

Y. Urata graduated in 1984 from the Department of

Mechanical Engineering, Tohoku University, Japan. Cur-

rently, he is a Chief Engineer at the Automobile R&D

Center of Honda Research and Development Co., Ltd.

His research interests include internal combustion en-

gines (gasoline), combustion analysis with visualization

technique, and variable valve trains. e-mail: Yasuhiro

Urata@n.t.rd.honda.co.jp.

L. Vervisch is a Professor at the National Institute of Ap-

plied Science of Normandy and Researcher at the CNRS

laboratory CORIA. He completed a Ph.D. in 1991 at Lab-

oratoire National d’Hydraulique in Chatou, followed by a

post-doc at the Center for Turbulence Research, Stanford

University, and then became a Junior Member of Institute

Universitaire de France in 2003. He uses direct numerical

simulations to understand laminar and turbulent ﬂames. He

also contributes to the development of subgrid-scale clo-

sures for large-eddy simulations and Reynolds-averaged

Navier–Stokes computations. Burners and aeronautical

and internal combustion engines are the main targets of

those studies. Vervisch is a co-editor of the journal Flow

Turbulence and Combustion. e-mail: vervisch@coria.fr.

D. Veynante got his Ph.D. from Ecole Centrale Paris in 1985

and joined the CNRS. His research is devoted to turbulent

combustion covering theoretical analysis, modelling, nu-

merical simulations, experiments, and corresponding data

processing. He has published more than 50 papers in inter-

national journals. He teaches combustion at Ecole Centrale

de Paris, Ecole Centrale de Nantes, and in various spring

or summer schools. He has co-authored a book titled The-

oretical and Numerical Combustion (Edwards, 2001, sec-

ond edition in 2005) with T. Poinsot and got the Grand

Prix Institut Franc¸ais du P

etrole from the French Sciences

Academy in 2003. Since 2007, he has also been Deputy Sci-

entiﬁc Director of CNRS Institute for Engineering and Sys-

tems Sciences (INSIS), in charge of about 50 labs working

on ﬂuid mechanics, combustion, heat transfer, plasma, and

chemical engineering. e-mail: denis.veynante@em2c.ecp.fr.

1 Fundamentals and Challenges

By N. Swaminathan and K. N. C. Bray

1.1 Aims and Coverage

Currently the energy required for domestic and industrial use and for transporta-

tion is predominantly met by burning fossil fuels. Although alternative sources are

evolving, for example, by harvesting wind and solar energies, energy production by

means of combustion is expected to remain dominant for many decades to come,

especially for high-power density applications. Thus pollutant emission regulations

for power-producing devices are set with the aim of reducing the impact of combus-

tion on the environment, both by curtailing pollutant emissions and by increasing

the efﬁciency of combustion equipment. Conventional combustion technologies are

unable to achieve these two demands simultaneously but fuel-lean combustion, in

which the fuel–air mixture contains a controlled excess of air, has the potential to

fulﬁl both requirements.

The aim of this book is to bring together a review of the physics of lean com-

bustion and its current modelling practices, together with a description of scientiﬁc

challenges to be faced and ways to achieve stable lean combustion in practical de-

vices. Additional material on non-reacting turbulent ﬂows may be found in [1–5],

and basic theories of combustion and turbulent reacting ﬂows and their governing

equations are presented in [6–9].

The present chapter sets the scene for the remainder of this volume. It has three

main aims: (1) to provide a brief review of the governing equations and auxiliary

relations that are required for the description of turbulent premixed combustion,

(2) to review the present status of the analysis of turbulent premixed combustion,

and (3) to identify ﬂame data that can be employed to verify modelling assumptions

and to propose experiments that could usefully add to such data. Different levels

of detail in numerical simulations are identiﬁed, and various regimes of combustion

are deﬁned. The important concept of a turbulent ﬂame speed is also introduced.

Although this quantity is central to some modelling methods, it can be deﬁned in

several different ways, and consequently comparisons between measurements and

theoretical predictions are often a difﬁcult task. The review provided here is not

intended to be exhaustive but to be sufﬁciently detailed in providing background for

later chapters. Earlier comprehensive treatments of turbulent premixed ﬂames are

provided in a number of references [e.g., 9–11].

2 Fundamentals and Challenges

Various modelling approaches are described in Chapter 2. As a consequence

of averaging, these models are required to provide statistical information related to

the unresolved small-scale structure of a turbulent ﬂame and the two-way interac-

tion between heat release and turbulence. It is intended that this presentation will

help the reader to appreciate the physics of lean premixed and partially premixed

ﬂames, its links to modelling, and the inter-relationship among the various modelling

approaches.

As we shall see, lean premixed ﬂames are inherently unstable, and thus the dis-

cussion would be incomplete without the description of various instability processes,

presented in Chapter 3. As explained there, the instabilities can be broadly classi-

ﬁed as thermodiffusive, hydrodynamic, and thermoacoustic, based on the physical

processes involved. Thermodiffusive instabilities are related to differences in the

diffusion rates of mass and heat to and from the ﬂame front, respectively. If the mass

diffusion rate of reactant to the ﬂame front is larger than the rate of heat diffusion

away from the front, t hen the ﬂame becomes unstable. The strong density jump

across a perturbed ﬂame front and the corresponding induced velocity changes lead

to an inherent thermal instability, called the Darrieus–Landau instability. When this

is coupled with buoyancy or an imposed pressure gradient, another hydrodynamic

instability, called Rayleigh–Taylor instability, results. Thermoacoustic oscillations re-

sult when heat release ﬂuctuations are in phase with ﬂuctuations in pressure. The

thermodiffusive and Darrieus–Landau instabilities are important in premixed lami-

nar ﬂames but are usually overwhelmed by sufﬁciently intense turbulence. However,

the Rayleigh–Taylor and thermoacoustic instabilities can play signiﬁcant roles in tur-

bulent ﬂames. The physics of these instabilities and methods to capture their effects

on turbulent premixed ﬂames are described in Chapter 3. The effects of thermoa-

coustic instabilities are of vital importance in gas turbine engines, so the science

behind them and various strategies adopted to control them are also fully discussed

in Chapter 3.

In appropriate circumstances, lean ﬂames emit a very low level of pollutants and

thus provide an ideal candidate for environmentally friendly engines and power-

generation devices. However, premixing of fuel and oxidiser must occur inside the

combustion chamber for safety reasons, creating only partially premixed reactants

because of the limited space and time available for mixing. Nevertheless, depending

on the level of partial premixing, it is still possible for a signiﬁcant proportion of the

combustion to occur in the premixed mode [12]. The scientiﬁc challenges involved in

achieving stable lean combustion in practical devices, the physical processes involved,

their interactions, and their modelling are all discussed in Chapter 4, in three different

perspectives. The ﬁrst section of Chapter 4 deals with the internal combustion (IC)

engines employing intermittent combustion along with a detailed review of emissions

legislation for automotive engines; the second and third sections consider continuous

combustion systems, but differentiate the requirements for and challenges in aero

gas turbines and their counterparts for power generation. This chapter also identiﬁes

some major challenges to be faced in future developments together with the factors

driving them.

Chapter 5 discusses possible methods and technologies to meet the demands of

the next and future generations of combustion devices. Scientiﬁc and technological

challenges are also identiﬁed, and these challenges are discussed in three different