Gaseous Detonations: Their nature, effects and control

265 Pages·1987·16.93 MB·English

by  Michael A. Nettleton (auth.)

Gaseous Detonations:
their nature, effects and control
Gaseous Detonations:
their nature, effects and control
MICHAEL A. NETILETON
LONDON NEW YORK
CHAPMAN AND HALL
First published in 1987 by
Chapman and Hall Ltd
11 New Fetter Lane, London EC4P 4EE
Published in the USA by
Chapman and Hall
29 West 35th Street, New York NY 10001
© 1987 Michael A. Nettleton
Softcover reprint of the hardcover 1st edition 1987
J. W. Arrowsmith Ltd, Bristol
ISBN -13: 978-94-010-7915-0
All rights reserved. No part of this book may be reprinted, or
reproduced or utilized in any form or by any electronic,
mechanical or other means, now known or hereafter invented,
including photocopying and recording, or in any information
storage and retrieval system, without permission in writing
from the publisher.
British Library Cataloguing in Publication Data
Nettleton, M. A.
Gaseous detonations: their nature and control
1. Gas dynamics 2. Explosions
3. Shock waves
1. Title
533' .293 QCl68.85.S45
ISBN -13:978-94-010-7915-0 e-ISBN-13 :978-94-009-3149-7
DOl: 10.1007/978-94-009-3149-7
Library of Congress Cataloging in Publication Data
Nettleton, Michael A. (Michael Arthur), 1932-
Gaseous detonations.
Bibliography: p.
Includes indexes.
1. Explosions. 2. Shock waves. 1. Title.
QD516.N4881986 620.8'6 86-13648
ISBN -13: 978-94-010-7915-0
Contents
Page
Preface ix
Foreword by Ya. B. Zel'dovich Xl
1 Introduction
1.1 General remarks 1
1.2 Definitions of commonly-used terms 2
1.3 Unidimensional models of detonations 5
1.4 Structure of a detonation wave 6
1.5 Philosophy of presentation 12
2 Unidimensional models 18
2.1 Introductory remarks 18
2.2 Properties of unidimensional shock waves 19
2.3 Properties of unidimensional shock waves with energy addition 22
2.4 Properties of the Chapman-Jouguet state 25
2.5 Comparison of C-J predictions and experiment 28
2.6 The Zel'dovich, von Neumann, Doring model 31
2.7 Comparison of the ZND model and experiment 34
2.8 The Taylor expansion wave 37
2.9 Concluding remarks 40
3 Structure of detonation fronts 42
3.1 General remarks 42
3.2 'Spinning' detonatipn fronts 44
3.3 'Galloping' fronts 51
3.4 Experimental studies of multi-headed fronts 53
3.5 Theoretical treatments of multi-headed fronts 61
3.6 Concluding remarks 66
4 Detonable media 69
4.1 General remarks 69
4.2 Confined and unconfined detonations 70
4.3 Gases and vapours which are detonable in the absence of an oxidant 73
vi Contents
4.4 Comparison of detonation limits for confined and unconfined
detonations with flammability limits for mixtures of hydrocarbons
with oxygen and air 75
4.5 Homology hypothesis for predicting detonation limits 80
4.6 Detonations with oxidants other than oxygen 82
4.7 Influence of initial pressure and temperature on detonability 83
4.8 Influence of additives on detonability 86
4.9 Detonations in suspensions of dusts and droplet mists in oxidizing
atmospheres 89
5 Initiation of a detonation wave 94
5.1 Cieneralremarks 94
5.2 Initiation of confined detonations by shock waves 95
5.3 Initiation by blast waves from electrical and laser sparks and
charges of conventional explosives 98
5.4 Detonations in large unconfined clouds of vapour 106
5.5 Minimum ignition energies 109
5.6 Laminar burning velocities 113
5.7 Expansion ratios 117
5.8 Detonations arising from accelerating flames 118
5.9 Influence of initial temperature and pressure of the medium on
run-up distances 125
5.10 Influence of diameter of pipeline on run-up distances 126
5.11 Effect of additives on pre-detonation distances 129
5.12 Effects of surface roughness and obstacles on the acceleration of
confined flames 131
5.13 Pressure piling (cascading) l32
5.14 Concluding remarks 133
6 Interaction of a detonation with confinement l36
6.1 Introductory remarks 136
6.2 Diffraction at an isolated wall, (Jw < 0° l38
6.3 Diffraction at an isolated wall, 0° < (Jw < (Jeri! 143
6.4 Diffraction at an isolated wall, (Jeri! < (Jw < 90°; standard two- and
three-shock theory for non-reactive \ media and \ the effects of
reaction 152
6.5 Normal reflection of a detonation wave 158
6.6 Transmission of a planar detonation wave through an abrupt
expansion in area 161
6.7 Propagation of detonations through bends and junctions 168
6.8 Interaction of a detonation with an inert surrounding gas 169
6.9 Refraction of detonations in mixtures of different composition 170
6.10 Concluding remarks 172
7 Damage caused by detonations 173
7.1 Introduction 173
7.2 Early experiments on effective pressures generated by detonations 176
7.3 Damage produced by detonations in chemical plant 179
7.4 Experimental studies of failure resulting from detonations 179
Contents vii
7.5 Concluding remarks 190
8 Prevention and mitigation of detonations 191
8.1 Introductory remarks 191
8.2 Inhibition of flames of normal burning velocity 193
8.3 Venting in the early stages of an explosion 195
8.4 Quenching offlame-shock complexes 197
8.5 Suppression of detonations 199
8.6 Mitigating the effects of detonations 204
8.7 Concluding remarks 207
9 Concluding recommendations 208
9.1 Introductory remarks 208
9.2 Stress waves in confining walls 211
9.3 Planned deformations as safety measures 212
9.4 Designing to minimize the effects of local peaks in pressure 213
9.5 Suggestions for further studies of detonations 215
References 219
Author index 241
Subject index 247
Preface
My introduction to the fascinating phenomena associated with detonation
waves came through appointments as an external fellow at the Department of
Physics, University College of Wales, and at the Department of Mechanical
Engineering, University of Leeds. Very special thanks for his accurate
guidance through the large body of information on gaseous detonations are
due to Professor D. H. Edwards of University College of Wales. Indeed, the
onerous task of concisely enumerating the key features of unidimensional
theories of detonations was undertaken by him, and Chapter 2 is based on his
initial draft. When the text strays to the use of we, it is a deserved acknow
ledgement of his contribution. Again, I should like to thank Professor D.
Bradley of Leeds University for his enthusiastic encouragement of my efforts
at developing a model of the composition limits of detonability through a
relationship between run-up distance and composition of the mixture. The
text has been prepared in the context of these fellowships, and I am grateful to
the Central Electricity Generating Board for its permission to accept these
appointments.
I am most grateful to Academician Ya. B. Zel'dovich for his agreeing to
spare some of his valuable time in commenting on the original draft and for
writing a foreword. Since he always keeps me on my toes with his appropriate
quotations from his encyclopaedic knowledge of the world's literature, it
behoves me to reply 1Tlill7'lX PEL, ov8ev /-LEVEi (Heraclitus, 513 Be). *
It is also appropriate to acknowledge with sincere thanks the efforts of
various illustrators who transformed my rough sketches into clear diagrams
and those of a number of typists who patiently resigned themselves to dealing
with numerous drafts of each chapter. Again, Dr G. O. Thomas, University
College of Wales, kindly performed the C-J calculations given in Chapter 2.
A special vote of thanks is due to Mrs J. Finnigan, a colleague at Central
* All is flux, nothing is stationary.
x Preface
Electricity Research Laboratories, who has painstakingly read both text
and references. The contributions to the text from many discussions with
co-workers in the field of detonations, too numerous to list individually, have
been of inestimable value and are gratefully remembered; hopefully with
complete accuracy.
Finally, an apology is owed to my daughters Naomi and Rebecca, for the
times at which progress on the book was painfully slow, and my patience with
them was not all that it should have been.
1985 Brockham
Betchworth
Surrey*
*A s from 1988 Department of Mechanical Engineering
University of Queensland
St Lucia
Queensland
Australia 4067
Foreword
The idea of detonation came into being after disastrous explosions in coal
mines more than a hundred years ago. The previous study of combustion
concerned the slow process. The safety-grid-protected lamp of Davy and 'The
story of a candle' by Faraday were the milestones of this line of investigation.
At first glance it was quite puzzling, how the slow subsonic combustion
could produce strong mechanical effects. The understanding came after the
laboratory experiments by the French investigators discovering the
detonation of combustible mixtures in glass tubes.
Another source of our knowledge and interest in detonation came from
pure theory. It is well known that the famous mathematician, Riemann,
obtained the shock waves in inert media literally on the tip of his pen. He has
shown that the movement of compressible gas leads to the formation of
breaks with abrupt rise of pressure, density and temperature - even if the
initial conditions were absolutely smooth. The contemporary reader would
point to the nonlinearity of gasdynamic equations; he would call Riemann the
ancestor of the modern catastrophe theory. The exact thermodynamics of the
shock waves were found by Hugoniot. The generalization to chemically active
media was not difficult and so the detonation theory of Chapman and Jouguet
was born with the birth of the 20th century.
A puzzling point remained. The shock wave amplitude was dependent on
the external causes of the shock. The detonation is a self-sustained process. Its
properties must depend solely on the energy, density and other characteristics
of the initial mixture. But formally the equations of Chapman and Jouguet
were consistent with a set of final states. The authors had to put forward a new
principle (minimal velocity or minimal entropy) in order to choose one point
of the set. The principle worked well and in good agreement with the
experiment. Still it had no firm theoretical foundation for forty years. It was
Zeldovich (1940), Doring (1942) and von Neumann (1943) who indepen
dently found the underlying idea of combustion initiated by the shock wave
xii Foreword
going ahead of the chemical reaction zone.
But even these works were not the end of the story. The mining industry
used high explosives. The detonation products with density more than twice
that of water are not ideal gases. The eminent theoretician, Landau, together
with Stanyukovich, has given an adequate description of the thermodynamics
for this case. It opened the experimental study of dynamical megabar
pressures. The money spent on Nobel prizes comes mainly from the solid
explosives industry.
The further development of gas detonation has shown a complicated
structure. The idealized Zeldovich-Doring-Neumann picture turned out to be
unstable in the realistic case of chemical reactions which are strongly
temperature dependent. An exact theory of detonation still does not exist!
A very important topic is the formation of detonation waves out of slow
combustion. The landmark here was Shchelkin's experiment - the magic
influence of a spiral turbilizing the gas motion before the flame. The role of
the internal instability of the plane slow flame (Landau, Darrieux) is still not
clear.
The purpose of the preceding short historical sketch ('all detonation in a
nutshell') is to give the reader the impression of how complicated and many
faced is the subject of detonation. It shows also the very difficult task
approached by the author - M. Nettleton. I do not think it is possible to make
a uniform coverage of all the field, but the author has chosen a very important
side of the problem. The main theme is the safety problems in handling
combustible gas or dust mixtures with air or oxygen. Important exceptions are
acetylene and ozone, which c~m detonate even in pure gas form, without air or
combustibles mixed in.
The importance of the subject is obvious. Explosions and especially
detonation in chemical industry lead to great life and economic losses. But the
complexity of the problem is immense simply because catastrophes are treated
by dealing with the unpredicted, situations not expected by the constructors.
In these ill-defined situations general knowledge plus common sense are more
useful than complicated mathematical theories and calculations.
I find the presentation by the author to be in accord with the goal. The book
consists of nine chapters. After the introductory one Chapters 2 and 3 deal
with the idealized and the real structure of the detonation wave.
The exposition is clear. An engineer or a student in technical sciences will
use it without trouble and without the necessity of using other literature.
As a wish for the second edition, I would mention the question of losses.
The losses of energy and impulse, as well as losses due to incomplete chemical
reaction, are important. They lead to a decrease of detonation velocity and
shock pressure as compared with the ideal thermodynamic calculation.
Finally if the losses are greater than some definite value, they lead to the
quenching of detonation. The theory of losses is made for a one-dimensional