Table Of ContentCombustion, Flames
and Explosions of Gases
Third Edition
Bernard Lewis
Ph.D., Sc.D. (Cantab.)
Guenther von Elbe
Ph.D. (Berlin)
Combustion and Explosives Research, Inc.
Pittsburgh, Pennsylvania
1987
ACADEMIC PRESS, INC.
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Library of Congress Cataloging in Publication Data
Lewis, Bernard, Date
Combustion, flames, and explosions of gases.
Includes index.
Ί. Combustion. 2. Flame. 3. Explosions. 4. Gases.
I. Von Elbe, Guenther, Date . II. Title.
QD516.L38 1987 665.7 86-20590
ISBN 0-12-446751-2 (alk. paper)
PRINTED IN THE UNITED STATES OF AMERICA
87 88 89 90 9 8 7 6 5 4 3 2 1
Preface to the Third Edition
This third edition of Combustion, Flames and Explosions of Gases adheres to the
basic purpose of this treatise as stated in the preface to the first edition, namely, to
provide the chemist, physicist, and engineer with the scientific basis for understanding
combustion phenomena.
The principal revision of the text concerns the oxidation kinetics of carbon mon
oxide and the much more ramified and complex oxidation kinetics of hydrocarbons.
The carbon monoxide-oxygen system is found to be so completely interlinked with
the well-understood hydrogen-oxygen system that in the total absence of hydrogenous
compounds no reaction path is discernible by which the latent enthalpy of the system
can be released in rapid reaction. This insight furnishes interpretations of phenomena
such as the steady and oscillatory glow described by Peter Gray and his colleagues.
The treatment of hydrocarbon oxidation kinetics has been completely revised pri
marily on the basis of re-examination of the excellent data that are found in earlier
literature. Newer investigations support and amplify the deductions drawn from this
earlier research. This confirms that careful and methodical investigations retain
validity, unaffected by the passage of time, even though the then available methods
of experimentation and data reduction were far removed from present techniques of
computerization and a plethora of modern sensing and recording devices.
In the past two decades computer programs have come into use to manage complex
problems of reaction kinetics. This is especially appropriate for high-temperature
reactions in hydrocarbon combustion such as occur in experimental flow systems and
in combustion waves. In such systems the overall reaction tends to go to completion
and in the course of this process virtually all imaginable reactions between the
reactants and the numerous intermediate products may take place. Whereas, we fully
agree that such problems are manageable only by means of computer techniques,
we have reservations with respect to other problems such as initiation of explosive
reactions in the stagnant gas of a reflected shock wave. Here, the initial concentration
of free radicals is virtually zero. Hence the initial reaction rate is very small or
imperceptible but builds up during an induction period to explosive proportions at a
self-accelerating rate. In the hydrocarbon chapter of this text, the treatments of such
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problems are given, which are based on the concept that the development of the
reaction rate from initially zero to explosive rates is governed by only a few chain-
branching and chain-breaking reactions and that reactions involving species that
appear only in the later stages of the overall reaction require no consideration.
Accordingly, no extensive catalogue of reactions is required, and the problem of the
induction period is approached by reaction-kinetic analysis rather than by computer
programs.
The reader will observe that a new concept has been developed in the interpretation
of the low-temperature oxidation of hydrocarbons, which is marked by the appearance
of the much-studied cool flames. We now discern two chain-branching reactions
referred to as chain branching by double peroxidation and by alkoxyperoxide dis
sociation. In conjunction with Benson's explanation of what was formerly referred
to as the "negative temperature" coefficient in hydrocarbon oxidation, it is now
possible to describe the whole range of phenomena occurring in this complex reaction
regime.
A vast number of investigations have been recorded in the literature that specializes
in combustion. Since 1962, 66 volumes of the Combustion Institute's Journal of
Combustion and Flame, 13 volumes of the International Combustion Symposia
published by the Institute, and numerous volumes of other journals, notably Com
bustion Science and Technology and Progress in Energy and Combustion Science
have made available an enormous number of generally excellent studies on details
of every aspect of combustion. It seems, however, that the conceptual basis of the
discipline had already been sufficiently established at the time of the appearance of
the previous edition of this book to make unnecessary a revision of the subject of
flame propagation in Part Π, except for some specific points meriting further attention.
For example, a new insight is offered on the relation between the experimental
minimum ignition energy of electric sparks and experimentally determined quenching
distances. Another example is the theoretical understanding of the observed increase
of the burning velocity with increasing pressure whenever the burning velocity
exceeds the order of 50-100 cm/sec and of the reversal of this effect when the
burning velocity is below this range. The explanation of this effect illustrates the
understanding that has been achieved concerning the role of chemistry in flame
propagation.
The state of the burned gas in Part ΙΠ had already been adequately treated in the
first edition. This also applies to the subject of internal combustion engines in
Part IV.
The authors acknowledge their indebtedness to Leland A. Watermeier, of the
Ballistic Research Laboratory, Aberdeen Proving Grounds, and to Robert S. Levine
of the National Bureau of Standards for a grant that enabled them to undertake a
study of the kinetics of oxidation of carbon monoxide on which Chapter HI is based.
In the preparation of Chapter VI the authors acknowledge with appreciation the
PREFACE TO THE THIRD EDITION xiii
advice and contributions of Béla Karlovitz. The Atlantic Research Corporation,
through the good offices of Edward Τ McHale, was most helpful in making available
graphic and computer facilities. Thanks are due to Hartwell F. Calcote of AeroChem
Research Laboratories, Inc., for fruitful discussion of the subject of ions in flames.
BERNARD LEWIS
Pittsburgh, Pennsylvania
GUENTHER VON ELBE
Alexandria, Virginia
May 1986
Preface to the Second Edition
The tempo of combustion research has continued unabated during the past decade.
Substantial progress has been made in establishing a common understanding of
combustion phenomena. However, this process of consolidation of the scientific
approach to the subject is not yet complete. Much remains to be done to advance
the phenomenological understanding of flame processes so that theoretical correla
tions and predictions can be made on the basis of secure and realistic models.
In this new edition particular emphasis has been placed on the modification of
combustion wave propagation due to heat loss to the unburned medium and to
localized changes of mixture composition by diffusion processes. Both influences
occur as a result of divergent propagation which takes place in a flow field with steep
velocity gradients or under conditions of flame initiation from a point source. The
heat loss effect imposes stability limits of flames in flow fields and minimal values
of flame diameter and ignition energy in flame initiation. Employing a new concept
of flame stretch, which refers to the growth of flame surface in divergent propagation,
it has been possible by similarity procedure to obtain good correlations of the
fundamental, measurable flame parameters of burning velocity and wave width with
flame stability limits and with spark ignition data. In this way, for example, the flame
stability limits on flame holders in high velocity streams have been deduced. Fur
thermore, it is shown that in all instances of divergent propagation diffusional
stratification of mixture composition occurs to a degree depending upon the relative
diffusivities of the fuel and oxidant components of the mixture. This stratification
produces effects that are predictable, at least qualitatively. Thus, in an over-rich
mixture of a heavy hydrocarbon and oxygen, the minimal flame diameter and minimal
ignition energy are smaller than predicted from the flame stretch equation for the
original mixture because oxygen diffuses into the flame zone more rapidly than fuel.
Similar considerations apply to flame stabilization. The concept of flame stretch and
diffusional stratification permits an understanding of limits of inflammability.
Other parts of this edition have not required the substantial revision given the
subject of combustion waves. However, some revisions have been made particularly
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in the discussion of detonation processes, and much new material has been included
where it appears to promote a better understanding of the subject.
BERNARD LEWIS
GUENTHER VON ELBE
Pittsburgh, Pennsylvania
February, 1961
Preface to the First Edition
During the past decade the scope and tempo of combustion research have increased
to such extent, and so many new facts and concepts have developed, that preceding
treatises appear to be wholly inadequate to meet the present day demands of student
and research worker for a modern exposition of the subject. Although the authors
have borrowed the title of their former book published in 1938, the present book
cannot properly be labeled a second edition inasmuch as the text is entirely new with
the exception of a few brief sections dealing with subjects that had already been well
explored at that time. The purpose of the new volume remains the same however,
namely to provide the chemist, physicist, and engineer with the scientific basis for
understanding combustion phenomena.
The terms combustion, flame, and explosion became part of the common
language long before clear scientific concepts existed, and therefore their usage has
remained somewhat arbitrary and flexible. In this book the treatment of the subject
matter comprises the theory of reaction chains and the chemical kinetics of reactions
between fuel gases and oxygen, the hydrodynamics of combustion waves, detonation
waves and jet flames, and the thermodynamics of combustion gases. In this respect
we have followed a plan used in the former book, which we believe has proven
valuable for delineating the field. Comparison of the state of knowledge 13 years
ago with that of today shows a considerable advance in the field of chemical kinetics,
a very large number of new facts and concepts in the field of ignition and combustion
wave propagation, and substantial progress in the understanding of diffusion flames
and detonation waves. On the other hand, the thermodynamic aspects of combustion
had already attained a degree of finality many years ago and therefore no significant
conceptual advances are to be noted, though the volume of reliable data has increased
markedly.
The reader will find new chemical mechanisms which have been deduced from
the latest available evidence and which should be regarded as the present best
judgment of the authors. These mechanisms are recommended as a basis for further
experimental work and discussion. There already exists a considerable area of
agreement among workers and it is hoped that the new analyses will contribute to its
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enlargement. The systems that have been treated are hydrogen and oxygen, carbon
monoxide and oxygen, and hydrocarbons and oxygen. The system best understood
is that of hydrogen and oxygen. In the carbon monoxide-oxygen system the reactive
mechanism appears to be approaching some degree of clarification although quan
titative data are still lacking. Considerable progress has been made in the understand
ing of the hydrocarbon-oxygen system and an early clarification of the oxidation
mechanism, at least for the lower members, appears to be distinctly possible. There
is also discernible a skeleton of consistent facts and theories of the oxidation of higher
hydrocarbons. Some interlinking and interdependence of the reaction mechanisms of
these systems are noted, and as further studies of selected mixtures are made the
requirement of interconsistency of reaction mechanisms will become a powerful
factor in the final elucidation of elementary chemical reactions.
In the second part of the book dealing with flame propagation, emphasis shifts
from reaction kinetics to hydrodynamics as the branch of science applicable to
combustion and detonation waves and the combustion of fuel jets. It is on the subject
of ignition and propagation of combustion waves that the greatest progress has been
made in recent years. For the first time one understands the relationship between
stabilization of combustion waves in burner flames and quenching in channels of
critical diameters. An understanding is also provided of the various phenomena of
flame propagation in tubes. A particularly significant advance is the integration of
the data on spark ignition with the concept of minimum ignition energy which is
derived from theoretical considerations of the development of combustion waves
from an ignition source. It is shown that the hydrodynamic equations can be simplified
to permit solutions which lead to correlation of the quenching distance with burning
velocity and other measurable quantities.
Important advances have been made by the recent theoretical and experimental
investigations of Karlovitz on the interaction between combustion waves and turbulent
motion in explosive gas mixtures. Very considerable progress is noted in the field of
combustion of laminar and turbulent fuel jets since the early work of Burke and
Schumann on laminar diffusion flames.
A theory of burner performance is made possible by combining the theory of air
entrainment of gas jets with the theory of flame stabilization. It is expected that this
development will find useful application to the problem of fuel interchangeability in
the gas industry. A discussion of this subject is included.
The theory of detonation waves, while already far advanced by the early work of
Chapman, Jouguet, and Becker, has been developed further by von Neumann and
by Brinkley and Kirkwood. New explanations are suggested for the frequently
observed discontinuous and spiral propagation of detonation waves. An insight is
gained into the wave structure and to the interaction between shock front and reaction
zone.
Fundamental research should ultimately contribute toward improved understanding
and control of technical combustion processes, particularly in engines. To accomplish
PREFACE TO THE FIRST EDITION xix
this it is necessary to analyze the engine process in terms of the fundamental physical
and chemical processes that occur in the various phases of starting and operation.
At present this has been pursued only to a very small extent. Too often engine studies
are confined to observations of the effect of fuel and engineering variables on over
all performance in a manner that excludes the possibility of recognizing the control
ling physical and chemical processes. While development of modern engines has
been erninently successful, this success has only been made possible by the accu
mulation of a very large volume of empirical information and by the continual
maintenance of large and costly testing facilities. The question may be asked whether
timely fundamental research could not have eliminated a large portion of this testing
that has been carried on and is still continuing on a worldwide scale, and whether
practical developments could not have been materially facilitated by scientific knowl
edge. In this text some attempt has been made to collect the meager information of
fundamental character, first, to show that in principle it appears to be quite feasible
to estimate the knock-limited performance of an Otto engine in a rather simple
manner, and second, to illustrate that in jet engines a close scrutiny of the flame
structure might lead to useful information on performance limits.
The authors are grateful to their colleagues in the Explosives and Physical Sciences
Division of the Bureau of Mines whose interest in and devotion to their researches
have materially assisted in providing the experimental basis of the newer concepts
of combustion wave propagation.
BERNARD LEWIS
GUENTHER VON ELBE
Pittsburgh, Pennsylvania
May 1951
