Recent work on gaseous detonations, CHEMIA I PIROTECHNIKA, Chemia i Pirotechnika

[ Pobierz całość w formacie PDF ]
Shock Waves (2002) 12: 3–12
Recent work on gaseous detonations
M.A. Nettleton
∗
Department of Mechanical Engineering, University of Queensland, Brisbane 4072, Australia
Received 9 September 1999 / Accepted 10 May 2001
Abstract.
The paper reviews recent progress in the field of gaseous detonations, with sections on shock
diffraction and reflection, the transition to detonation, hybrid, spherically-imploding, and galloping and
stuttering fronts, their structure, their transmission and quenching by additives, the critical energy for
initiation and detonation of more unusual fuels. The final section points out areas where our understanding
is still far from being complete and contains some suggestions of ways in which progress might be made.
Key words:
Review, Detonation, Unsteady waves, Gaseous explosion, Damage
1 Introduction
onation. However, bends are often made of more ductile
mildsteel to prevent fragmentation under the influence
of the higher pressure as the front reflects. It is common
practice with explosive dusts to buildplant andits con-
tainment as lightweight as possible, andrely on a combina-
tion of fittedvents andfailures of the structure to prevent
the formation of a detonation. Clearly, information on the
behavior of light andmassive components of both ductile
andbrittle materials are requiredboth to design plants
and to predict from any resultant damage, whether they
have been subjectedto a detonation.
In the past decade there have been a number of reviews
of detonations, but only two of these have concentrated
on safety aspects. For instance that by Clarke (1989) is
strongly biasedtowards a mathematical analysis of the
acceleration of flames fuelledby a single step reaction.
There must be questions about the inaccuracies involved
in treating the chain reactions of both gaseous oxidation
anddecomposition of self-combusting fuels in terms of
a single rate constant, probably more so for the former
than the latter, where there is a significant shortening in
the number of steps. In this context, explosions of dust-
oxidant systems are generally believed to be homogeneous.
Accepting the uncertainty in chemical kinetics, the paper
forms an ideal introduction to analytical techniques for
predicting the transition from deflagration to detonation
(DDT).
Lee (1991) gives a complete rehearsal of the reasons
compelling a belief in the multi-dimensional nature of det-
onation fronts. I have lookedat the nature of detonation
fronts in ram accelerators, where detonations are driven
between a projectile andits containment walls in mixtures
of unusual composition at pressures of up to 25 bar in at-
mospheres of unusual composition (Nettleton 2000). The
paper gives details of the interaction of shocks with walls
andreaction zones together with details of the interaction
of a planar detonation with a surrounding medium, which
can either be inert or of different composition.
Now seems to be an appropriate time to review progress on
my suggestions (Nettleton 1987) for further work in the
fieldof gaseous detonations. I make no apology for my
focus on safety aspects. Recall that Dixon (1893, 1903)
startedwork in this area, following a gaseous detona-
tion in a town gas main in London. My introduction was
through a series of explosions during start-up and shut-
down of turbulent flows of suspensions of coal dust in
air in pipelines, running between mills on the basement
floor andburner nozzles in the walls of modern (typi-
cally 500 MW) pulverized-fuel fired plant. During normal
operation, concentrations of dust in these are above the
upper flammability limit, so that unsafe conditions are
of very short duration. A wide variety of plant may be
threatenedby the possibility of a detonation either in the
gaseous phase, by a self-decomposing material, by a mix-
ture of fuel and oxidant or by a flammable dust suspen-
sion. It is often possible to design to contain the effects
of an unreflecteddetonation; for instance, straight runs of
pipelines can, without excessive cost penalties, be made
thick enough to cope with the results of an unreflected
detonation. Problems, however, will occur at any bends.
The German hydrocarbon-synthesis industry in the 1940s
adopted a different approach, seeking to prevent the det-
onation of acetylene, either pure or diluted by inert addi-
tives, by tightly packing all containment anddesigning to
cope with any resulting deflagration. This was a remark-
able feat, with packedpipes andvessels withstanding the
results of bombing attacks.
Dust suspensions in power stations flow through cast-
iron pipelines, designed to be thick enough to withstand
erosive wear of particles of pure silica, andthus, in their
unworn state, are capable of containing an unreflecteddet-
Present address:
11GrendonClose,Horley,SurreyRH68JW,
UK (e-mail: MNettl5993@aol.com)
∗
4
M.A. Nettleton: Recent work on gaseous detonations
Of the two papers dealing more directly with safety
concerns, Gelfandet al. (1991) show that much valuable
information is still derivable from uni-dimensional treat-
ments. In particular, Russian work following on from that
of Zel’dovich for uni-dimensional waves with heat losses to
walls or to inert or reacting particles in the flow is compre-
hensively covered. Prior to this many of the reports had
only been available in Russian. The most recent by Moen
(1993) covers DDT in clouds of fuel in air. The costs and
problems in siting andchoosing suitable instrumentation
for studies of explosions of large, say greater than 50 m,
flattenedandnon-hemispherical clouds with fuels much
denser than the surrounding air are considerable, so that
much depends on the scaling laws chosen to extrapolate
from small-scale tests.
The present review assumes familiarity with the con-
tents of these earlier ones andgoes on to discuss safety as-
pects of confinedandunconfinedfronts. In particular, sec-
tions deal with progress in understanding processes such
as shock diffraction andreflection, DDTs, hybriddetona-
tions, spherically imploding fronts, galloping and stutter-
ing waves, front structure, transmission of the wave, the
use of additives to quench detonations, those in less com-
mon fuels andcritical energies for their initiation.
trajectory of the triple point. Edwards et al. (1984) show
these are of particular importance at low angles of the
wedge. A somewhat similar paper by Li et al. (1997) com-
pares theoretical andexperimental results for the angle of
the oblique reflection of detonation waves in dilutedand
undiluted mixtures of oxyhydrogen, assuming coupling of
leadfront andreaction zones. Again the theoretical results
are very sensitive to the assumed degree of overdrive.
The critical diameter problem for the transition from
planar to spherical detonation continues to excite atten-
tion andhas recently been reviewedby Lee (1996). Jones
et al. (1995) have produced a mathematical model to ac-
count for the effects of cell spacing in oxyhydrogen mix-
tures diluted by argon on transmission in two-dimensional
expansions. Again, Pantow et al. (1996) have examined
experimental andtheoretical results for the propagation
of detonations in oxyhydrogen mixtures through sudden
expansions. They obtainedclose agreement with exper-
iment using the random generation of numerical noise
to produce the transverse fronts. They do not comment
upon the mechanism whereby certain fronts grow whilst
others decay. Gamezo et al. (1998) in a study of planar
shocks also usednumerical noise to impose disturbances
andshow that the front is unstable to perturbations with
wavelengths greater than one to two reaction zone half-
widths. The noise was found to govern the initial process,
but not the final spacing of transverse fronts. An increase
in the energy of activation leads to the formation of a
more irregular structure. Jones et al. (1996) have taken
a somewhat different approach in their theoretical model-
ing of an expanding front, complimenting that of Pantow
et al. (1996), but lack an experimental validation of their
analysis.
2 Influence of containment
on detonation structure
The explosion in the nuclear plant at Three Mile Island
has resulted in a wide range of studies of the reactivities
of mixtures of oxygen, nitrogen, steam andhydrogen, see
for instance Tieszen (1993). Particularly notable is that
by Boyack et al. (1993) who start with the proviso that
the components are likely to be su
?
ciently massive for
their associatedtime constants to be very much longer
than the rise-time andprobably the duration of the pres-
sure pulse. It shouldbe notedthat is by no means gener-
ally true for other types of plant. They report on some of
the mechanisms leading to enhancement in pressure, such
as DDT or the presence of thin layers of inert materials.
Whilst detonation velocities can be reduced by their pres-
ence (Gelfand et al. 1991) the momentum, depending on
mass, may not. Their analysis shows that edges and cor-
ners can enhance pressures predicted from normal reflec-
tion andthat peak pressures are a function of equivalence
ratio andthe thickness of the layer of inert gas.
Extending earlier theoretical studies in the application
of the Chester-Chisnell-Whitham (CCW) relationship for
detonations in convergent channels, Bartlma (1990) and
Li andBen-Dor (1998) examineddetonative flows over
wedges, correcting the strong shock approximation to al-
low for a change in ratio of specific heats across the front.
The implicit assumption here appears to be that the re-
action zones assume a similar shape to that of the leading
front. A comparison of theory with experiment suggests
that the optimal agreement with experiment is obtained
by assuming a degree of overdrive of 10%. Furthermore,
there remain questions about the effects of cell size on the
3 The transition from deflagration
to detonation
This is an area which has receivedmuch attention over
the last decade. It is one that also creates some prob-
lems with a number of papers impinging on topics with
which I have chosen to deal separately. Possibly an ideal
starting point is the paper by Chue et al. (1993) giving a
numerical analysis of the structure of fronts travelling ap-
proximately at the speedof soundin the hot combustion
products. Interesting papers by Zhang et al. (1992, 1998)
return to the Craven andGreig (1968) postulate of max-
imum pressures being generatedby a transition process
which produces a precursor front with a reflected shock
travelling back through this zone. Their theoretical pre-
dictions are compared with measurements of pressure in
an endslug of aluminium dust in a mixture of acetylene
in air. Here peak pressures were up to twice those for the
homogeneous explosive mixture. It cannot be too strongly
emphasisedhow important inhomogeneities in the mix-
ture are in determining final pressures.
Ciccarelli et al. (1994) have extended previous work
on DDT in hydrogen-steam-air mixtures at ambient tem-
peratures up to 650 K, about that anticipatedto have
M.A. Nettleton: Recent work on gaseous detonations
5
occurredin the Three Mile Islandexplosion, using tubes
containing a number of orifice plates. These provedto be
successful for mixtures of composition such that cell spac-
ing was close to the diameter of the orifice.
Saurel et al. (1992) have shown that distances for DDT
are reduced when the initiation source is a hot plasma.
They give a numerical treatment for laser initiation in a
two phase medium, emphasising the care which must be
taken in the choice of an appropriate equation of state;
see also Fujiwara et al. (1994) for further details of com-
putational analysis of laser supporteddetonations in ho-
mogeneous mixtures.
Johnson et al. (1996) have examinedthe influence of
two flame inhibitors, both halogenatedhydrocarbons, on
transition distances in mixtures of methane, propane and
acetylene with air. In each case the velocity of the flames
in obstacle-filledtubes was reducedand, with a su
?
cient
amount of inhibitor, quenched.
A series of papers from Moscow State University on
theoretical andexperimental studies of DDT for homo-
geneous and droplet dispersions in air have recently ap-
peared, see Smirnov and Tyurnikov (1994, 1995), Smirnov
et al. (1995, 1997), Smirnov andPanfilov (1995). They ex-
tendthe range of fuels testedto, for example,
n
-methyle-
necyclopropane and
n
-decane (see section on less usual
fuels). Smirnov et al. (1997) give details of rates of wall
loads to be expected in the event of the reflection of the
detonation formed under different scenarios.
Following Teodorczyk’s (1995) work on the role of in-
stabilities in promoting turbulence andthus flame accel-
eration resulting in DDT, Khokhlov et al. (1997) postu-
late that transition occurs via the formation of gradients
producedby a combination of turbulent mixing andlocal
quenching of the flame. A further paper by Khokhlov et
al. (1999) gives a numerical approach to the role of shock-
reaction zone interactions in turbulent flows. Obara et al.
(1996) present the results of a high speedschlieren study
of DDT in oxyhydrogen mixtures with different degrees
of dilution by nitrogen in obstacle-filled channels. Local
overdriven fronts travelling at up to twice the C-J velocity
were observed. Chue et al. (1995) have conducted a theo-
retical andexperimental investigation of the transition in
oxyacetylene mixtures diluted by argon. In order to obtain
fast deflagrations, wire screens were used to suppress any
transverse structure. However, transverse pressure waves
rapidly reformed, eventually to produce transverse reac-
tion fronts, following their interaction with the leading
shock. Teodorczyk et al. (1988) have also photographed
the propagation of quasi-detonations in mixtures of hydro-
gen, ethylene andpropane with oxygen in obstacle-filled
rectangular tubes.
Carnasciali et al. (1991) have studied the initiation of
detonation in ethylene, acetylene, propane and hydrogen
in mixtures of oxygen andnitrogen by a turbulent jet of
hot gases (see also Achasov et al. (1995) in Sect.10). They
concluded that there is a critical ratio of size of jet orifice
to cell width that is comparable with that of 13, the ratio
of tube diameter to cell width, necessary for the initiation
of spherical fronts. It is unfortunate that Khokhlov et al.
(1999) do not appear to make any use of the data from
these experimental studies.
Brown andThomas (1999) have measuredignition de-
lays in the temperature range 1073 to 2211 K in both
ethylene andpropane dilutedby varying amounts of either
argon or nitrogen andcombinedthese with spark schlieren
photographs of shock reflection, ignition andtransition to
detonation. They show that only a complex, and inor-
dinately expensive to compute, kinetic scheme involving
some 600 reaction steps predicts accurately delays to ig-
nition.
Two relatedpapers (Frolov et al. 1994; Noscov et al.
1995) deal with numerical investigations of the effects of
auto-ignition in the wall boundary layer of homogeneous
mixtures. The resultant flame can propagate at close to
the local velocity of sound, leading to strong coupling be-
tween energy release andlocal pressure fronts.
Starikovskii (1996) has examinedthe ignition andtran-
sition process in nitrous oxide/carbon monoxide/hydrogen
mixtures diluted by helium. Undiluted mixtures have some
interesting characteristics, including the possibility of su-
per-equilibrium concentrations of carbon dioxide and the
potential existence behindreflectedshocks of gas-dynamic
perturbations leading to DDT. Both theory and experi-
ment reveal that single andtwo-phase modes occur and
are controlledby a combination of the total heat release
andthe ratio of induction andexothermic reaction times.
Recent papers on DDT in dust suspensions include
that by Klemens et al. (1994) who foundthat the presence
of inert particles of quartz hadlittle influence on transition
distances. However, they produced a linear decrease in
flame velocity andfinally extinction. Li et al. (1995a,b) in
two very similar papers deal with the transition of dust
layers deposited on walls of tubes. Their principal finding
is the importance of inhomogeneities in concentration in
determining DDTs.
Corn-starch is a frequent choice for the combustible
dust, see for instance Zhang and Gronig (1989, 1991) who
studiedtransition processes in both oxygen andair. They
give further results in a subsequent combinedexperimen-
tal paper (Zhang et al. 1992). They acknowledge the im-
portance of non-uniformities, andmake every attempt to
reduce these, as far as possible and succeeded in produc-
ing runs with a deviation of less than 0.5% in a series of
15 experiments in a 140 mm diameter tube with a ratio of
L/d
of 124. A numerical analysis by Hayashi et al. (1994)
of two-phase detonation processes in suspensions of starch
in air suggests that a one-step reaction mechanism su
?
ces
to produce satisfactory predictions of C-J velocities and
distances for ignition and transition to detonation. How-
ever, they appear only to validate their velocities with
results from some unspecifiedsource (a referee graciously
informs me that they usedthe data of Zhang andGronig
1989, 1991).
A further paper on dust deposits by Fan and Li (1996)
deals with wall deposits of 15
rmµ
m particles of alu-
minium andtwo condensedexplosives, RDX andHMX,
andis mainly concernedwith differences between theoret-
ical andexperimental C-J velocities. In a combinedtheo-
6
M.A. Nettleton: Recent work on gaseous detonations
retical and experimental study Fedorov et al. (1996) also
chose suspensions of aluminium dust, this time in oxygen.
Alexander et al. (1993) describe experiments on various
dusts, both in suspensions and in wall layers, using both
mildandsevere forms of ignition. For suspendeddusts
both sources result in the formation of a detonation. How-
ever, with layers of dust mild sources are more successful
than are blast waves. The experiments took place in three
forms of confinement, a vertical tube of moderate length,
a larger diameter horizontal tube and an explosion gallery
with ignition via a flame in a methane/air mixture. Da-
hab et al. (1989) obtainedtransition in coal dust-oxygen
mixtures in a vertical tube when the ignition source was
of low energy. Finally, Korobeinikov (1993) has produced
a theoretical analysis of the important parameters govern-
ing the onset of detonations in suspensions of dusts and
pointedout the problems in formulating laws governing
scaling from small to large scale detonations, particularly
unconfinedones.
ing imploding fronts with temperatures between 10
7
and
10
8
K at the focus. The extreme precautions in construc-
tion of the apparatus requiredto ensure symmetry means
that such events are not likely to occur in normal plant.
6 Galloping and stuttering fronts
These terms imply the continuous cycling of fronts from
velocities well in excess of the C-J value to one consid-
erably below it. Experiments examining such phenomena
must be carriedout in straight tubes of at least tens of me-
ters in length to ensure the existence of their cyclic nature.
When numbers of sharp bends are present, for instance in
polymerizing plant for the production of polyethylene, dis-
tances may be sharply reduced. However, it is di
?
cult to
visualize such conditions occurring frequently in plant.
Dupre et al. (1986, 1990, 1991) andLee et al. (1995a,
1995b) in a series of experiments, using different moni-
toring techniques, demonstrate that the phenomena can
occur for a wide range of hydrocarbons in stoichiomet-
ric mixtures with both oxygen andnitrous oxide. Ishii
andGronig (1998) showedthat the phenomenon is not
confinedto hydrocarbons, but can also occur with low
pressure mixtures of oxyhydrogen, so that the phenomena
cannot be accountedfor by the more complex reaction
schemes of the hydrocarbons.
4 Hybrid detonations
The hybridterm refers to a combination of fuels, gener-
ally particles with a more detonable gas. However, I am
presently extending its use to cover dust cloud containing
other forms of sensitisers. In a pair of papers Veyssiere and
Khasainov (1995) andKhasainov andVeyssiere (1996) set
out to examine the nature of fronts in suspensions of alu-
minium powder in oxyhydrogen mixtures. The first uses
a ZND model of the front with heat losses to predict the
existence of three regimes, pseudo-gas, single and dou-
ble detonation fronts. The second, an experimental paper
searches for these and concludes that the first decays to
a single front while the latter two appear to be stable. A
more recent paper by Veyssiere et al. (1999) deals again
with clouds of starch in oxyhydrogen mixtures. The the-
oretical analysis involves the particles heating to an igni-
tion temperature of 700 K in oxygen, close to the value
foundby Nettleton andStirling (1967) for coal particles
in shockedoxygen, followedby the production of a homo-
geneous flame. Discrepancies in velocities in the various
studies of clouds of starch outlined in the previous section
are attributedto changes in particle size, dimensions and
layout of the tubes.
Wolinski et al. (1996) demonstratedthat hybriddeto-
nations of oats dust are achieved in methane/air mixtures
for methane concentrations of 8.5 to 14.5% anddust con-
centrations not greater than 0.1 kg/m
3
. Higher loadings of
dust act as a suppressant. Finally, Tulis (1989) describes
how unconfined detonations of aluminium powder in air
can be generatedin the presence of 5% nitroguanidine act-
ing as a sensitiser. As far as I am aware, this is the first
report of unconfined detonations of dusts in air.
7 Structure of fronts
Before discussing recent papers in this field, I should draw
attention to the availability of much experimental data
on spacing of fronts on the internet. Valuable addresses
∼
mikek/detn
−
db and
−
db/html/, see Kane-
shige andShepherd(1997).
Of late there has been much work on numerical mod-
elling of confineddetonations in both homogeneous and
dusty gases. For example, Lefebvre and Oran (1995) have
examinedshock structures in oxyhydrogen mixtures heav-
ily diluted by argon. They suggest that the degree of re-
lease of energy is concentratedclose to the triple point and
its level increases as a triple point approaches another or
the wall. From the same school, Williams et al. (1996)
numerically model how, in the absence of wall losses, the
complexity of structure of transverse waves increases with
a change from 2 to 3 dimensions, with two perpendic-
ular modes accounting for the slapping wave frequently
observedin experiments. Further, the interaction of these
waves produces the vortex fieldwhich entrains unburnt
mixture behindthe Mach stem. Another theoretical pa-
per by Oran et al. (1998) uses a detailed kinetic scheme
to demonstrate that two-dimensional models indicate the
possibility of a secondrelease of energy two thirds along
the cell length of detonations in oxyhydrogen mixtures di-
lutedby argon.
Fujiwara andWashiku (1994) have also studiedthe
structure of fronts in oxyhydrogen mixtures using a sim-
plifiedkinetic scheme. For spinning waves, they propose
5 Spherically-imploding fronts
Two papers by Terao andWagner (1991), Terao et al.
(1995) describe the construction of an apparatus produc-
M.A. Nettleton: Recent work on gaseous detonations
7
that the diameter of the tube should lie between 1.8 and
3.4 cell widths. Bauer et al. (1986) examined the influence
of initial pressure using an optical technique to measure
cell lengths in three fuels, propane, ethylene andmethane,
mixedwith oxygen andnitrogen. The most reliable results
were for pressures between 3 and50 bar in propane air
mixtures, from 1 to 10 bar in mixtures of ethylene, with
oxygen andnitrogen andfrom 0.5 to 15 bar for diluted
oxymethane mixtures. They also show that a constant of
29 relates ignition distances with cell lengths throughout
the pressure range.
Uphoff et al. (1996) tackle numerically the di
?
cult
problem of the structure of detonations in the oxidation
of carbonaceous materials in oxygen. Together with the
combination of di
?
culties imposed by the choice of ap-
propriate heat andmass transfer relationships, the exis-
tence of complex chemical kinetics might be anticipated.
Experimental verification also poses problems, both from
the viewpoints of constant shape, size distribution and
uniformity in dispersion.
Stewart et al. (1996) in a somewhat contentious paper,
see questioners’ comments, derive explicit criteria for cell
spacing andaspect ratios for weakly curvedwaves in me-
dia with high activation energies. Their theory is based on
the formation of pulsating waves leading to cellular insta-
bilities. It seems doubtful that chain reactions, involved in
most oxidation processes, correspond with their proviso.
Beeson et al. (1991) have given experimental results
for cell sizes of fronts in
n
-hexane andcommercial jet fuel
in a nitrogen-oxygen mixture over the range 0
<x<
3
.
8,
where
x
is the ratio of nitrogen to oxygen at 300 K. Tieszen
et al. (1991) give experimental andtheoretical results for
cell sizes in some 20 hydrocarbons with significantly differ-
ent chemical characteristics. Surprisingly, for a standard
composition they vary only from 40 to 50 mm, within the
experimental error between two competent observers of
soot tracks.
Stamps andTieszen (1991) andCiccarelli et al. (1994)
in response to the explosion at Three Mile Islandhave de-
terminedcell sizes in mixtures of hydrogen, air anddilu-
ents. Both deal with the effects of both initial pressure
andtemperature on spacing. Terao andMotoyama (1992)
extendmeasurements in the influence of temperature on
detonation velocities in oxypropane over the range from
400 to 700 K.
Tulis et al. (1993) working with aluminium powder sus-
pensions in air sensitised by the addition of RDX demon-
strate that it is possible to obtain both single headed
andmultiple fronts. As with their paper on unconfined
fronts (Sect.4), this is the first paper to report upon multi-
headed fronts in clouds of dust in air. Their experiments
also revealedsignificant differences in the performance
of atomizedaluminium, less than 5
µ
m, andflakedalu-
minium, equivalent to spherical particles less than 1
µ
m
in diameter.
Nettleton and Teodorczyk (1992) endeavor to estimate
the characteristic size of a model scramjet which, were
mixing of air andhydrogen su
?
ciently fast, wouldbe
capable of supporting a standing detonation. Again on
oxyhydrogen mixtures Ohyagi et al. (1992) used pressure
measurements, relating falls in pressure andMach num-
ber with the development of size of cells. Lastly, Lee et al.
(1995b), in an attempt to remove the uncertainties associ-
ated with individual interpretations of widths of cells, have
investigatedthe use of digital analysis of smokedfoils.
8 Transmission of fronts
For convenience this section is divided into transmission
through concentration gradients and through roughened
or obstacle-filledcontainment. Recent theoretical papers
include that of Voronin and Mitranov (1991). An early
paper paying great attention to any mixing occurring be-
tween filling andfiring a shock tube was that by Thomas
et al. (1991). It demonstrated that improvements can be
made to the Paterson (1953) model of refraction of the
shock by taking into account the Taylor expansion and
losses to the walls. Kuznetsov et al. (1997) examinedthe
fate of waves travelling from stoichiometric oxyhydrogen
into an inert medium; in this case, either argon, helium,
nitrogen or carbon dioxide. The effectiveness of quenching
was foundto be proportional to the molecular weight and
inversely proportional to the specific heat ratio of the inert
material. Kryuchkov et al. (1996) in a theoretical paper
examine the propagation of a detonation of a width which
increases linearly under the influence of a decreasing re-
action rate. The critical conditions for the gradient in re-
activity is deduced by solving the continuity equations for
a one-step Arrhenius kinetic model. Their prediction for
moderate values of the effective activation energy suggest
the distance for failure is of the order of 10 cell lengths.
Teodorczyk and Lee (1995) extended by Teodorczyk
andBenoan (1996) describe experiments on the role of
wall layers in attenuating transverse waves and quench-
ing fronts. A further paper from Lee’s group, Makris et
al. (1995) shows that results for the influence of a porous
structure in attenuating fronts can be correlatedby the
empirical relationship
V/V
∗
=1
−
0
.
35log(
d
#
/d
), where
d
# and
d
are the critical tube diameter, representing mix-
ture sensitivity andthe pore size.
Teodorczyk and Thomas (1995) in an experimental
study explain how acoustically absorbing walls and air
gaps quench andre-initiate detonations. Lyamin et al.
(1991) review andextendRussian work on hydrogen,
acetylene andpropane mixtures with air andoxygen in
porous media. For the latter, only C-J fronts were found
to be stable in all media, when the mixtures are at or
close to stoichiometric. The different regimes experienced
with mixtures that are far from being stoichiometric and
at pressures well below the critical value are described.
9 Quenching by additives
Two papers deal with experiments on the effectiveness of
halogenatedhydrocarbons in quenching establisheddet-
onations (Lefebvre et al. 1995; Evariste et al. 1996). Of
[ Pobierz całość w formacie PDF ]

  • zanotowane.pl
  • doc.pisz.pl
  • pdf.pisz.pl
  • tejsza.htw.pl

    •