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1.
Large scale experiments on detonation initiation in gasoline-air by two different sources were carried out at stoichiometric
conditions. Unconfined clouds of volume generated by a special facility had a shape of semicylinder of 15–17 m in length and 6–8 m in radius. Both the charge
of condensed HE and the charge of stoichiometric propane-air were used to initiate detonation in the mixture. In case of initiation
by a propane-air charge the critical initiation energy was up to 7 times as large as that for HE initiation. The detonation
cell size for gasoline-air was determined as 0.04–0.05 m. It was shown, that the well-known correlation between the critical
energy of point blast initiation and the cell size failed for this system. The cell size obtained is close to one of propane-air,
but no direct transfer of detonation from one mixture to another was observed.
Received 10 March 1995 / Accepted 12 March 1995 相似文献
2.
A study on jet initiation of detonation using multiple tubes 总被引:1,自引:0,他引:1
A detonator consisting of a dense bundle of small-diameter tubes (4.4–19 mm) is tested experimentally using stoichiometric
mixtures of hydrogen–oxygen and hydrogen–air. Tests are conducted in a 5,200-mm long detonation tube fitted with a schlieren
photograph section and smoked foil to record the deflagration to detonation (DDT) transition. It is confirmed that the flame
jet emanating from the tube assembly causes detonation initiation immediately downstream of the detonator, with little dependence
on the size of the detonation tube. For the fuel–air mixture, the insertion of Shchelkin spirals into each of the smaller
tubes enhances the development of the turbulent flame jet, leading to a shorter DDT distance. Multi-point spark ignition is
also shown to provide a further reduction in the DDT distance compared to single-point ignition.
PACS 47.40.-x; 47.40.Nm; 47.70.Fw; 82.40.-g; 82.40.Fp 相似文献
3.
The propagation mechanism of high speed turbulent deflagrations 总被引:2,自引:0,他引:2
The propagation regimes of combustion waves in a 30 cm by 30 cm square cross–sectioned tube with an obstacle array of staggered
vertical cylindrical rods (with BR=0.41 and BR=0.19) are investigated. Mixtures of hydrogen, ethylene, propane, and methane with air at ambient conditions over a range
of equivalence ratios are used. In contrast to the previous results obtained in circular cross–sectioned tubes, it is found
that only the quasi–detonation regime and the slow turbulent deflagration regimes are observed for ethylene–air and for propane–air.
The transition from the quasi–detonation regime to the slow turbulent deflagration regime occurs at (where D is the tube “diameter” and is the detonation cell size). When , the quasi–detonation velocities that are observed are similar to those in unobstructed smooth tubes. For hydrogen–air mixtures,
it is found that there is a gradual transition from the quasi–detonation regime to the high speed turbulent deflagration regime.
The high speed turbulent deflagration regime is also observed for methane–air mixtures near stoichiometric composition. This
regime was previously interpreted as the “choking” regime in circular tubes with orifice plate obstacles. Presently, it is
proposed that the propagation mechanism of these high speed turbulent deflagrations is similar to that of Chapman–Jouguet
detonations and quasi-detonations. As well, it is observed that there exists unstable flame propagation at the lean limit
where . The local velocity fluctuates significantly about an averaged velocity for hydrogen–air, ethylene–air, and propane–air mixtures.
Unstable flame propagation is also observed for the entire range of high speed turbulent deflagrations in methane–air mixtures.
It is proposed that these fluctuations are due to quenching of the combustion front due to turbulent mixing. Quenched pockets
of unburned reactants are swept downstream, and the subsequent explosion serves to overdrive the combustion front. The present
study indicates that the dependence on the propagation mechanisms on obstacle geometry can be exploited to elucidate the different
complex mechanisms of supersonic combustion waves.
Received 5 November 2001 / Accepted 12 June 2002 / Published online 4 November 2002
Correspondence to: J. Chao (e-mail: jenny.chao@mail.mcgill.ca)
An abridged version of this paper was presented at the 18th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Seattle, USA, from July 29 to August 3, 2001. 相似文献
4.
Comparison of critical conditions for DDT in regular and irregular cellular detonation systems 总被引:1,自引:0,他引:1
Abstract. The results of an experimental study of DDT in mixtures with regular and irregular detonation cellular structures are presented.
Experiments were carried out in a tube 174 mm i. d. with obstacles (blockage ratios were 0.1, 0.3, and 0.6). Mixtures used
were hydrogen–air and stoichiometric hydrogen–oxygen diluted with , Ar, and He. The critical conditions for DDT are shown to depend on the regularity of the cellular structure of test mixtures.
The critical values of the cell sizes in Ar- and He-diluted mixtures are shown to be significantly smaller than those in -diluted mixtures. This means that systems with a highly regular detonation cellular structure have far less capacity for
undergoing DDT compared to irregular ones with the same values of detonation cell sizes.
Received 18 November 1999 / Accepted 15 May 2000 相似文献
5.
Detonation initiation is investigated in aluminium/oxygen and aluminium/air mixtures. Critical conditions for initiation of
spherical detonations are examined in analogy with the criteria defined for gaseous mixtures, which correlate critical parameters
of detonation initiation to the characteristic size of the cellular structure. However, experimental data on the detonation
cell size in these two-phase mixtures are very scarce, on account of the difficulty to perform large-scale experiments. Therefore,
2D numerical simulations of the detonation cellular structure have been undertaken, with the same combustion model for Al/air
and Al/O2 mixtures. The cell size is found to be λ = 37.5 cm for a rich (r = 1.61) aluminium–air mixture, and λ = 7.5 cm for a stoichiometric aluminium-oxygen mixture, which is in reasonable agreement with available experimental data.
Calculations performed in large-scale configurations (up to 25 m in length and 1.5 m in lateral direction) suggest that the
critical initiation energy and predetonation radius for direct initiation of the unconfined detonation in the aluminium–air
mixture are, respectively, 10 kg of TNT and 8 m. Moreover, numerical simulations reveal that the structure of the detonation
wave behind the leading front is even more complicated than in pure gaseous mixtures, due to two-phase flow effects.
This paper is based on work that was presented at the 21st International Colloquium on the Dynamics of Explosions and Reactive
Systems, Poitiers, France, July 23–27, 2007. 相似文献
6.
S. P. Medvedev S. V. Khomik H. Olivier A. N. Polenov A. M. Bartenev B. E. Gelfand 《Shock Waves》2005,14(3):193-203
Initiation of detonation by a turbulent jet of combustion products has been studied in a detonation tube of 141 mm inner diameter.
Jet formation techniques based on either a perforated plate or bursting membrane subjected to the impact of a stable detonation
wave were utilized. Critical conditions of detonation initiation in hydrogen–air and hydrogen–oxygen–nitrogen mixtures have
been found to depend on both the mixture sensitivity and the geometrical parameters of the arrangement.
PACS 47.70.Fw; 82.33.Vx; 82.40.Fp
This paper was based on work that was presented at the 19th Inter-national Colloquium on the Dynamics of Explosions and Reactive
Systems, Hakone, Japan, July 27 - August 1, 2003 相似文献
7.
Effect of scale on the onset of detonations 总被引:6,自引:0,他引:6
S.B. Dorofeev V.P. Sidorov M.S. Kuznetsov I.D. Matsukov V.I. Alekseev 《Shock Waves》2000,10(2):137-149
Critical conditions for onset of detonations are compared at (1) two significantly different scales, (2) for a range of -air mixtures diluted with C, O, and (3) for two types of geometry – one a long obstructed channel and the other a room with a relatively small aspect ratios.
For the range of scales, mixtures, and initial conditions tested, the detonation cell size was shown to be a reliable scaling parameter for characterization of detonation onset conditions. An experimental correlation
is suggested for the critical detonation onset conditions. This correlation is based on a wide variety of available experimental
data on DDT in mixtures of hydrogen and hydrocarbon fuels with air and on the use of detonation cell size as a scaling parameter characterizing the mixture.
Received 14 November 1999 / Accepted 16 February 2000 相似文献
8.
An experimental study was carried out to investigate flame acceleration and deflagration-to-detonation transition (DDT) in
fuel–air mixtures at initial temperatures up to 573 K and pressures up to 2 atm. The fuels investigated include hydrogen,
ethylene, acetylene and JP-10 aviation fuel. The experiments were performed in a 3.1-m long, 10-cm inner-diameter heated detonation
tube equipped with equally spaced orifice plates. Ionization probes were used to measure the flame time-of-arrival from which
the average flame velocity versus propagation distance could be obtained. The DDT composition limits and the distance required
for the flame to transition to detonation were obtained from this flame velocity data. The correlation developed by Veser
et al. (run-up distance to supersonic flames in obstacle-laden tubes. In the proceedings of the 4th International Symposium
on Hazards, Prevention and Mitigation of Industrial Explosions, France (2002)) for the flame choking distance proved to work
very well for correlating the detonation run-up distance measured in the present study. The only exception was for the hydrogen–air
data at elevated initial temperatures which tended to fall outside the scatter of the hydrocarbon mixture data. The DDT limits
obtained at room temperature were found to follow the classical d/λ = 1 correlation, where d is the orifice plate diameter and λ is the detonation cell size. Deviations found for the high-temperature data could be
attributed to the one-dimensional ZND detonation structure model used to predict the detonation cell size for the DDT limit
mixtures. This simple model was used in place of actual experimental data not currently available.
PACS 47.40.-x; 47.70.Fw
This paper was based on work that was presented at the 19th Interna-tional Colloquium on the Dynamics of Explosions and Reactive
Sys-tems, Hakone, Japan, July 27 - August 1, 2003 相似文献
9.
The cellular detonation structure has been recorded for hybrid hydrogen/air/aluminium mixtures on 1.0 m 0.110 m soot plates. Addition of aluminium particles to the gaseous mixture changes its detonation velocity. For very fine
particles and flakes, the detonation velocity is augmented and, in the same time, the cell width diminishes as compared with the characteristic cell size of the mixture without particles. On the contrary, for large particles, the detonation velocity decreases and the cell size
becomes larger than . It appears that the correlation law between the cell size and the detonation velocity in the hybrid mixture is similar to
the correlation between the cell size and the rate of detonation overdrive displayed for homogeneous gaseous mixtures. Moreover,
this correlation law remains valid in hybrid mixtures for detonation velocities smaller than the value D of the mixture without particles.
Received 10 May 2001 / Accepted 12 August 2002 Published online 19 December 2002
Correspondence to: B. Veyssiere (e-mail: veyssiere@lcd.ensma.fr) 相似文献
10.
Yu. V. Tunik 《Journal of Applied Mechanics and Technical Physics》2016,57(6):963-970
The problem of initiation and stabilization of detonation combustion of a hydrogen–air mixture injected into an axisymmetric channel with a finite-length central body in a flow with a Mach number M0 = 5–9 is solved. It is numerically demonstrated that the presence of the central body both in a convergent–divergent nozzle and in an expanding channel leads to stabilization of detonation combustion of a stoichiometric hydrogen–air mixture at free-stream Mach numbers M0 > 7. Various channel configurations that ensure different values of thrust generated by detonation combustion of a stoichiometric hydrogen–air mixture are compared. 相似文献
11.
Behavior of detonation waves in mixtures with concentration gradients normal to the propagation direction was studied experimentally.
Mixtures with various concentration gradients were formed by sliding the separation plate which divides a detonation chamber
from a diffusion chamber in which a diffusion gas was initially introduced. A stoichiometric hydrogen–oxygen mixture was charged
in the detonation chamber, while oxygen or nitrogen was filled in the diffusion gas chamber. Temporal concentration measurement
was conducted by the infrared absorption method using ethane as alternate of oxygen. Smoked foil records show a deformation
of regular diamond cells to parallelogram ones, which well corresponds to local mixture concentration. Schlieren photographs
reveal the tilted wave front whose angle is consistent with the deflection angle of the detonation front obtained from trajectories
of the triple point. The local deflection angle increases with increase in local concentration gradient. Calculation of wave
trajectory based on the ray tracing theory predicts formation of the tilted wave front from an initial planar front.
相似文献
12.
In the frame of industrial risk and propulsive application, the detonability study of JP10–air mixtures was performed. The
simulation and measurements of detonation parameters were performed for THDCPD-exo/air mixtures at various initial pressure
(1 bar < P
0 < 3 bar) and equivalence ratio (0.8 < Φ < 1.6) in a heated tube (T
0 ~ 375 K). Numerical simulations of the detonation were performed with the STANJAN code and a detailed kinetic scheme of the
combustion of THDCPD. The experimental study deals with the measurements of detonation velocity and cell size λ. The measured
velocity is in a good agreement with the calculated theoretical values. The cell size measurements show a minimum value for
Φ ~ 1.2 at every level of initial pressure studied and the calculated induction length L
i corresponds to cell size value with a coefficient k = λ/L
i = 24 at P
0 = 1 bar. Based on the comparison between the results obtained during this study and those available in the literature on
the critical initiation energy E
c, critical tube diameter d
c and deflagration to detonation transition length L
DDT, we can conclude that the detonability of THDCPD–air mixtures corresponds to that of hydrocarbon–air mixtures.
This paper is based on the work presented at the 33rd International Pyrotechnics Seminar, IPS 2006, Fort Collins, July 16–21, 2006. 相似文献
This paper is based on the work presented at the 33rd International Pyrotechnics Seminar, IPS 2006, Fort Collins, July 16–21, 2006. 相似文献
13.
S. B. Dorofeev A. V. Bezmelnitsin V. P. Sidorov J. G. Yankin I. D. Matsukov 《Shock Waves》1996,6(2):73-78
Large scale experiments (50 m3) have been carried out on the initiation of detonation by means of a jet of hot combustion products. The effects of hydrogen
concentration (18–30% vol.), jet orifice diameter (100–400 mm), and the mixture composition in constant volume explosion chamber
(25–50%) were investigated. Both high enough hydrogen concentration and large enough jet size are necessary for detonation
initiation. The minimum values are within the ranges of 20 to 25% vol. H2, and of 100 to 200 mm correspondingly. A minimum ratio of jet size and mixture cell width 12–13 is required for detonation
initiation. 相似文献
14.
The effect of initial pressure on aluminum particles–air detonation was experimentally investigated in a 13 m long, 80 mm diameter tube for 100 nm and 2 μm spherical particles. While the 100 nm Al–air detonation propagates at 1 atm initial pressure in the tube, transition to the 2 μm aluminum–air detonation occurs only when the initial pressure is increased to 2.5 atm. The detonation wave manifests itself in a spinning wave structure. An increase in initial pressure increases the detonation sensitivity and reduces the detonation transition distance. Global analysis suggests that the tube diameter for single-head spinning detonation or characteristic detonation cell size would be proportional to (d
0: aluminum particle size, p
0: initial pressure). Its application to the experimental data results in m ~ O(1) and n ~ O(1) for 1 to 2 μm aluminum–air detonation, thus indicating a strong dependence on initial pressure and gas-phase kinetics for the aluminum reaction mechanism in detonation. Hence, combustion models based on the fuel droplet diffusion theory may not be adequate in describing micrometric aluminum–air detonation initiation, transition and propagation. For 2 μm aluminum–air mixtures at 2 atm initial pressure and below, experiments show a transition to a “dust quasi-detonation” that propagates quasi-steadily with a shock velocity deficit nearly 40% with respect to the theoretical C–J detonation value. The dust quasi- detonation wave can propagate in a tube with a diameter less than 0.4–0.5 times the diameter required for a spinning detonation wave. 相似文献
15.
16.
The current ram accelerator operations have shown that data on the ability of the propellants to detonate are required. Previous
studies examined the efficacy of initiation techniques based on piston impact. The purpose of the present work is to analyze
the effects of detonation wave transmission from a detonating mixture into a low sensitivity mixture. One-dimensional modeling
based on the analysis of pressure vs particle velocity for the mixtures is used to interpret experimental data. Furthermore,
calculations based on chemical kinetics (CHEMKIN code) are provided. Experimental data together with the modeling of the detonation
transmission provide some new insight into the limiting conditions necessary to establish a Chapman-Jouguet (CJ) wave in a
detonable mixture.
Received 11 January 2000 / Accepted 15 September 2000 相似文献
17.
An experimental investigation was performed to establish the dependence of concentration limits of detonation re-initiation
behind a multi-orifice plate on mixture composition and initial pressure for hydrogen–air mixtures. The experiments were carried
out in detonation tubes of diameter 106 and 141 mm, separated by a multi-orifice plate into two sections. The tubes were equipped
with pressure gauges and a semi-cylindrical smoked plate. It is shown that initial pressure has strong influence on the value
of concentration limit, especially for lean hydrogen–air mixtures. On the basis of soot records it can be inferred that re-initiation
occurs due to two different mechanisms that depend on the mixture sensitivity and properties of the multi-orifice plate. 相似文献
18.
Boris Khasainov Henri-Noel Presles Daniel Desbordes Pietro Demontis Pierre Vidal 《Shock Waves》2005,14(3):187-192
An experimental study of the detonation diffraction from 26- and 52-mm inner diameter tubes to cones of various angles α in
stoichiometric acetylene/oxygen mixture allowed us to determine critical conditions for diffraction and to detail the mechanisms
involved. All soot-foil records show that critical transmission is due to super-detonation propagating transversally in shocked
gas before the decoupled flame front. However, at large cone angles (α > 40∘), super-detonation originates at the axis of the flow and propagates tangentially to the cone wall (this situation is close
to detonation transmission to a space and a half-space). At smaller angles (i.e. α < 40∘), on the opposite, super-detonation originates at the cone wall and propagates toward the axis. In addition the soot plates
often give some evidence that, during escape of detonation products from the tube, a Mach disk is formed at a distance of
about one tube diameter from the tube exit. Numerical two-dimensional simulations of detonation diffraction favorably agree
with the observations.
PACS 47.40.-x
This paper was based on work that was presented at the 19th Inter-national Colloquium on the Dynamics of Explosions and Reactive
Systems, Hakone, Japan, July 27 - August 1, 2003 相似文献
19.
Using a 90mm-bore, 3.15 m long detonation tube, experimental detonation characteristics (detonability limits, detonation
velocities and peak pressures) of stoichiometric methane-oxygen-diluent mixtures at an initial pressure up to 3.5 MPa have
been experimentally investigated. A parametric study has been carried out as a function of both amount and nature of diluent,
namely carbon dioxide, nitrogen and helium. The experimental results allowed the adjustment and validation of computations
of the Chapman-Jouguet characteristics by means of a thermochemical code. These experimental data associated with validated
computations provide a valuable tool, among others, for the choice of the most appropriate mixture composition in the superdetonative
combustion mode for ram accelerator (ramac) experiments. The investigations were organized to determine the upper detonable
areas of dense ternary mixtures, and to provide detonation velocity data in order to adjust a series of intermolecular parameters
involved in the thermochemical code.
Received 8 May 1997 / Accepted 15 December 1997 相似文献
20.
We analyse the processes which occur when a planar detonation propagating from the fixed end of a donor explosive charge
impacts on an acceptor homogeneous explosive. We propose a model for estimating the minimal length of the donor charge for
which an explosion can be generated in the acceptor. We show that the self-similarity of the donor flow imposes a minimal
length on the donor charge so its piston effect be capable of keeping the volumetric-expansion rate of the shocked acceptor
to small-enough values and, thereby, of triggering explosion in a finite time. The donor detonation is represented as a Chapman-Jouguet
discontinuity; the chemical decomposition in the acceptor is described by the Arrhenius global rate law. The model reproduces
the experimental trend according to which the smaller minimal lengths are obtained with donor explosives that have larger
heats of reaction and initial pressures. The minimal lengths predicted by the model agree well with those obtained by means
of one-dimensional numerical simulations. Additional simulations show that the minimal length for generating an explosion
is smaller than, but perhaps of the same order as, the minimal length for generating a transition to detonation. Further work
is necessary to (i) analyse the case of donor explosives with finite reaction rates, and to (ii) account for the detonation
cellular structure in the simulations of shock-to-detonation transitions.
Received 21 December 2001 / Accepted 15 July 2002 Published online 4 November 2002
Correspondence to: Pierre Vidal
An abridged version of this paper was presented at the 18th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Seattle, USA, from July 29 to August 3, 2001 相似文献