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1.
Recent work on gaseous detonations 总被引:1,自引:0,他引:1
M.A. Nettleton 《Shock Waves》2002,12(1):3-12
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.
Received 9 September 1999 / Accepted 10 May 2001 相似文献
2.
Non-equilibrium model of steady detonations in aluminum particles - oxygen suspensions 总被引:3,自引:0,他引:3
Steady-state detonation regimes are studied on the basis of the mathematical model of detonation of aluminum particles in
oxygen taking into account differences in velocities and temperatures of the mixture components. The final steady state is
analyzed by determining the types of final singularities in the plane of relaxation parameters (the ratios of characteristic
times of thermal and velocity relaxations and combustion). The regions of existence of steady-state regimes are found numerically,
depending on the detonation wave velocity and relaxation parameters. Numerical illustrations of various flow types are presented,
and the properties of the detonation wave structure caused by velocity nonequilibrium are examined. Qualitative agreement
of data obtained with frozen relaxation parameters and their dependence on the flow parameters is shown.
Received 5 July 1997 / Accepted 13 July 1998 相似文献
3.
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
4.
Explosive dispersal of solid particles 总被引:3,自引:0,他引:3
Abstract. The rapid dispersal of inert solid particles due to the detonation of a heterogeneous explosive, consisting of a packed bed
of steel beads saturated with a liquid explosive, has been investigated experimentally and numerically. Detonation of the
spherical charge generates a blast wave followed by a complex supersonic gas-solid flow in which, in some cases, the beads
catch up to and penetrate the leading shock front. The interplay between the particle dynamics and the blast wave propagation
was investigated experimentally as a function of the particle size (100–925 m) and charge diameter (8.9–21.2 cm) with flash X-ray radiography and blast wave instrumentation. The flow topology during
the dispersal process ranges from a dense granular flow to a dilute gas-solid flow. Difficulties in the modeling of the high-speed
gas-solid flow are discussed, and a heuristic model for the equation of state for the solid flow is developed. This model
is incorporated into the Eulerian two-phase fluid model of Baer and Nunziato (1986) and simulations are carried out. The results
of this investigation indicate that the crossing of the particles through the shock front strongly depends on the charge geometry,
the charge size and the material density of the particles. Moreover, there exists a particle size limit below which the particles
cannot penetrate the shock for the range of charge sizes considered. Above this limit, the distance required for the particles
to overtake the shock is not very sensitive to the particle size but remains sensitive to the particle material density. Overall,
excellent agreement was observed between the experimental and computational results.
Received 16 August 1999 / Accepted 26 June 2000 相似文献
5.
为了研究装置点火延迟时间对不同浓度粉尘爆炸压力和压力上升速率的影响,以铝粉为介质在5L圆柱形爆炸装置中进行系列爆炸实验。结果表明:装置点火延迟时间对铝粉爆炸压力和压力上升速率有十分显著的影响,且存在一个最佳点火延迟时间,此时最大爆炸压力最大;随着铝粉浓度的增加,最佳点火延迟时间先增加后保持不变。最佳点火延迟时间下的最大爆炸压力和最大压力上升速率明显高于点火延迟时间固定为60s时的。相对粉尘不同浓度均采用固定点火延迟时间,不同浓度时采用最佳点火延迟时间,所测得的粉尘最大爆炸压力和最大压力上升速率明显符合实际。
相似文献6.
Analysis of available data on dependence of the critical detonation diameter of various heterogeneous condensed explosives on mean size of grains and voids demonstrated that in many cases surprising
correlations between and the initial specific surface area of heterogeneous explosives exist, namely, or . The run distance to detonation in wedge test with sustained strong shock of constant amplitude also linearly correlates
with , i.e. .
At the same time, the shock sensitivity reversal effect is often observed when grain size of HE is reduced. Apart from that
Moulard (1989) found that detonation critical diameter of plastic bonded explosive with mono- and bimodal RDX grain size distribution
depends nonmonotonously on mean grain size.
Complicated dependence of shock sensitivity of heterogeneous explosives on their specific surface area can be explained based
on comparison of the critical hot spot size at given characteristic pressure behind shock wave with the mean heterogeneity size . At high characteristic pressure (relative to the critical ignition pressure) is small compared with and all specific surface area of heterogeneous explosive is available for the hot spot growth process in accordance with
the grain burn concept.
However, when characteristic pressure of shock wave decreases, increases and can become comparable with . In this case only relatively large potential hot spots with size can result in self-supported hot spot growth process and shock sensitivity is controlled by the specific surface area which
corresponds to only larger heterogeneities and can be significantly smaller than initial specific surface area.
Received 18 July 1996 / Accepted 6 November 1996 相似文献
7.
A.M. Milne 《Shock Waves》2000,10(5):351-362
The mechanisms of detonation propagation in heterogeneous systems comprising closely packed particles and a liquid explosive
are not fully understood. Recent experimental work has suggested the presence of two distinct modes of detonation propagation.
One mode is valid for small particles (which is the regime we will address in this paper) with another mode for large particles.
In this work we model numerically the detail of the wave interactions between the detonating liquid and the solid particles.
The generic system of interest in our work is nitromethane and aluminium but our methodology can be applied to other liquids
and particles. We have exercised our numerical models on the experiments described above. Our models can now qualitatively
explain the observed variation in critical diameter with particle size. We also report some initial discrepancies in our predictions
of wave speeds in nominally one dimensional experiments which can be explained by detailed modelling. We find that the complex
wave interaction in the flow behind the leading shock in the detonating system of liquid and particles is characterised by
at least two sonic points. The first is the standard CJ point in the reacting liquid. The second is a sonic point with respect
to the sound speed in the inert material. This leads to a steady state zone in the flow behind the leading shock which is
much longer than the reaction zone in the liquid alone. The width of this region scales linearly with particle size. Since
the width of the subsonic region strongly influences the failure diameter we believe that this property of the flow is the
origin of the observed increase in failure diameter with particle size for small inert particles.
Received 3 December 1999 / Accepted 5 July 2000 相似文献
8.
This paper presents results from an experimental study of transmission of gaseous detonation waves through various granular
filters. Spherical glass beads of 4 and 8 mm diameter and crushed rock of 7.5 mm volume averaged diameter were used as filter
material. Varying the initial pressure of the detonating gas mixture controlled the detonation cell size. Dilution with argon
was used to vary the detonation cell regularity. The complete range from almost no detonation velocity deficit to complete
extinction of the combustion wave was observed. The existing correlation for gaseous detonation velocity deficit where is the critical diameter for the gaseous detonation and is the pore size, is found to be applicable for both smooth spherical particles and irregular crushed rock when considering
irregular detonation structures. Soot films and pressure measurements show that as the detonation cell size is increased,
reinitiation of a reanular filter until it finally no longer occurs at . Complete extinction of the combustion wave occurs at . These two limits appear to be about the same for irregular and regular detonation cell structures. For irregular structures
without argon dilution, can be found for detonation wave failure, and can be found for complete extinction of the combustion wave. For argon dilution these limits are changed to and , respectively. The data are a bit scarce as a basis for proposing a new correlation for regular structures, but as a first
approximation log is suggested for regular structures. The detonation or combustion wave is found to approach a constant velocity in the granular
filter if not extinguished.
Received 31 October 2001 / Accepted 15 July 2002 Published online 4 November 2002
Correspondence to: T. Slungaard (e-mail: slung@maskin.ntnu.no)
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
9.
Yu.V. Tunik 《Shock Waves》1999,9(3):173-179
In the present paper the direct initiation of a self supporting detonation and propagation of a low-speed combustion in methane-air-coal
particles mixtures are solved. For particles, a heterogeneous regime of combustion is used, for methane one overall chemical
reaction is taken into account: CH + 2O = CO + 2HO. The heat release rate is assumed to be defined as a delay time based on the well-known thermal theory of Frank-Kamenetsky
(1967). The proposed model allows one to investigate the influence inert particles or coal dust on the explosion limits of
methane-air mixtures. It is shown that the addition of a limited quantity of particles leads to detonation stability. In low
speed combustion problems this method allows one to get a good correlation between theoretical and experimental velocities
of steady flame propagation in carbon-hydrogen gaseous mixtures. Coal dust influence on gasdynamics of a methane-air mixture
combustion is investigated in an unsteady problem by using of the global modelling. It is shown that limited coal dust concentration
increases the flame wave intensity in lean methane-air mixtures in contrast to inert particles. In stoichiometric gas mixtures,
sand and coal dusts decrease a flame velocity. Far from the ignition point flame, the velocity is largely defined by the dust
mass concentration and not by the size of particles.
Received 5 July 1997 / Accepted 13 July 1998 相似文献
10.
Detailed observation of deflagration to detonation transition (DDT) is inherently difficult. This is primarily due to the
stochastic nature of flame acceleration and shock formation processes that in most practical situations give rise to the conditions
required for detonation to emerge. The present paper describes how shock tube techniques have been used to control the conditions
required for the onset of detonation. The paper first outlines some initial experiments involving turbulent flame acceleration
before concentrating on experiments in a reflected shock mode. To aid interpretation of the observations the paper also presents
a simple gasdynamic analysis of particle trajectories and considers the various physical and chemical processes that could
lead to the onset of detonation.
Received 27 November 2001 / Accepted 28 January 2002 相似文献
11.
Detonation and deflagration initiation at the focusing of shock waves in combustible gaseous mixture 总被引:12,自引:0,他引:12
B.E. Gelfand S.V. Khomik A.M. Bartenev S.P. Medvedev H. Grönig H. Olivier 《Shock Waves》2000,10(3):197-204
Abstract. Detonation and deflagration initiation under focusing conditions in a lean hydrogen-air mixture was experimentally investigated.
The experiments were carried out in a shock tube equipped with the laser schlieren system and pressure transducers. Two-dimensional
wedges (53° and 90°), semi-cylinder and parabola, were used as the focusing elements. The peculiarities of mild and strong
ignition inside the reflector cavity were visualized. A hydrogen-nitrogen mixture was taken for comparison between reactive
and inert mixture. It was found that mild ignition inside the reflector cavity can lead to detonation initiation outside the
cavity. Schlieren pictures of the process were obtained and the dependence of the distance of detonation initiation on Mach
number of the incident shock wave was established.
Received 30 August 1999 / Accepted 23 February 2000 相似文献
12.
The ignition and combustion process of fuels in a supersonic combustion chamber plays an important role in the design of hypersonic
propulsion system. However, it is a quite complicated process, due to the large variation of inlet air velocity, temperature,
oxygen concentration, and shocks in the supersonic combustion chamber. The purpose of this paper is to observe the ignition
delay and combustion phenomenon of the JP-8 fuel droplets in a supersonic flowfield experimentally. A shock tube is used as
a basic test facility to create a high-speed and high-temperature flowfield as a supersonic combustor. In the experiments,
several test parameters are controlled, such as shock velocity, gas temperature, fuel droplet size and distance, initial fuel
temperature, and oxygen concentration, etc. The test results show the influence of these parameters on ignition delay, ignition
limitation, and detonation. The most important factor in the experiment is the initial fuel temperature effect, which is influenced
by the altitude variation during a flight.
Received 4 August 1995 / Accepted 12 December 1995 相似文献
13.
Shock waves generated by projectile impacts were transmitted into hexane and the shocked hexane was analyzed by TCD-GC, FID-GC,
GCMS, and FABMS for produced aliphatic hydrocarbons. The projectile length and its velocity were varied from 10 to 40 mm and
from 220 to 1040 m/s, respectively. The initial temperature of the hexane was 77, 193 and 273 K. The major products detected
throughout the reactions were hydrogen, light alkanes from C to C, and light alkenes from C to C. The minor products were heavy alkanes from C to C and soot-like materials. Experiments with varied projectile length revealed that the shock reaction occurred only while the
shock wave was transmitted through hexane (about seconds). This short reaction time may be responsible for a lower yield of branched products in the shock reaction compared
with yield produced by hexane pyrolysis in previous studies. In the shock reaction of hexane, the dehydrogenation was one
of the important reactions and the recombination of hexyl radicals might play a role in the formation of -C. Experiments with varied initial temperature suggested that the molar yield of products depends not on the shock temperature
but on the shock pressure, and that the reaction mechanisms for solid hexane and for liquid hexane are not identical. As the
shock pressure increased, the relative yield of heavy products increased while that of light products decreased. This could
be interpreted mainly by considering the activation volumes of the reaction involved.
Received 12 September 1997 / Accepted 14 October 1997 相似文献
14.
为了研究瓦斯的爆炸危险性,选取对其影响较大的初始温度和初始压力进行实验研究。运用特殊环境20 L爆炸特性测试系统,对不同初始温度(25~200 ℃)和初始压力(0.1~1.0 MPa)条件下瓦斯的爆炸极限、最大爆炸压力和点火延迟时间进行实验研究。结果表明:高温高压条件使瓦斯的爆炸上限升高、下限降低,爆炸极限范围扩大;随着初始温度升高,瓦斯爆炸的最大爆炸压力逐渐减小;初始温度越高,点火延迟时间越短。通过对实验结果的分析,运用安全原理知识和危险度定义,给出初步评估瓦斯爆炸危险性的方法。 相似文献
15.
Explosion characteristics of coal gas under various initial temperatures and pressures 总被引:2,自引:0,他引:2
Explosion limits data are essential for a quantitative risk assessment of explosion hazard associated with the use of coal gas. The present work is to investigate the influence of various initial temperatures and pressures on explosion characteristics of coal gas/air mixture. The explosion limits and the minimum ignition energy of coal gas/air mixture are obtained experimentally at various temperatures ranging from 20 to 80°C and pressures ranging from 0.1 to 0.2 MPa. An empirical equation is established from the experimental results for the effects of initial temperatures and pressures on explosion limits. By adding diluent (nitrogen) into coal gas/air mixtures, the dilution effects on the explosion limits have been explored as well, and a critical flammable concentration of coal gas is determined to be at 7.4–9.0% by volume. By means of a high-speed digital video camera, the flame front development is recorded and analyzed. The tests are carried out with lean, stoichiometric and rich mixtures of coal gas in air under the conditions of initial pressure and nitrogen addition. Furthermore, the influence of the initial pressure and the concentration on the explosion pressure is measured and compared against theoretical results, where a good agreement is observed. 相似文献
16.
Effect of obstacle size and spacing on the initial stage of flame acceleration in a rough tube 总被引:5,自引:0,他引:5
Experiments were conducted to study flame acceleration in an orifice plate laden detonation tube. Orifice plate area blockage
and spacing were varied to determine their affect on flame acceleration. The tube used in the study was 3.05 m long with an
inner diameter of 14.0 cm. Experiments were primarily carried out with stoichiometric propane-air, however the affect of mixture
reactivity was also investigated by varying the mixture equivalence ratio. The distance required for the flame to achieve
a velocity equal to the speed of sound in the unburned gas mixture was measured. This run-up distance is used to characterize
the early stage of the flame acceleration process. It was found that in all cases, the flame run-up distance decreased with
increased blockage ratio and with increased mixture reactivity. It was found that for higher blockage ratios plates flame
acceleration was greatest for a plate spacing of one tube diameter, but for lower blockage ratio plates the results obtained
for one-half, one, and one and one-half tube diameter plate spacing were very similar. The most rapid flame acceleration was
observed when the ratio of the orifice plate spacing and the orifice plate height (half of the difference between the tube
and orifice plate diameter) is on the order of 5. It is proposed that this optimum acceleration corresponds to the condition
where the plate spacing is roughly equal to the length of the unburned gas re-circulation zone downstream from the orifice
plate.
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
17.
18.
Experimental and numerical studies on transmission of gaseous detonation to a less sensitive mixture
A phenomenon of detonation transmission from one gaseous mixture (donor) to another of lower sensitivity (acceptor) was studied
experimentally and numerically. The objective was to study effects of a donor mixture length and acceptor mixture sensitivity
on the possibility of detonation transmission. Experiments were carried out in detonation tube 9.5–12 m long and 174 mm id.
Three types of donor mixtures were used in the driver: stoichiometric acetylene/air, stoichiometric hydrogen/air, and 20%
of hydrogen/air. Air mixtures with 14–29.6% of hydrogen were used as acceptors. Driver length varied from 0.17 to 5.6 m. Detonation
transmission was studied for an abrupt opening of interface between two mixtures. Series of 1D and 2D calculations were made
to simulate the problem numerically. Both, results of experiments and calculations revealed a set of parameters that effect
transmission process. Critical conditions were determined as minimum driver length expressed in terms of characteristic chemical
reaction length scales of acceptor mixture. They were shown to depend on differences in reaction rates and energy contents
of donor and acceptor mixture.
Received 6 January 1997 / Accepted 20 March 1997 相似文献
19.
旋转爆轰胞格结构的实验和数值研究 总被引:6,自引:0,他引:6
对爆轰波在环形圆管(预混气体为2H2/O2/Ar)内的传播分别进行了实验和数值研究。实验研究
采用烟迹板记录了环形圆管内爆轰波的胞格结构。数值计算利用二阶附加半隐的Runge-Kutta法和五阶
WENO格式分别离散欧拉方程的时间和空间导数项,采用基元反应简化模型描述化学反应过程,得到了旋转
爆轰的流场及数值胞格结构。实验和数值模拟结果表明:爆轰波在圆环管中传播时,由于圆环的内壁发散、外
壁收敛,圆环内侧爆轰强度小于外侧,胞格尺寸较大;内侧OH 的分布区域大于外侧,浓度较低。旋转爆轰的
这种性质,使爆轰波能以稳定的角速度绕轴旋转。 相似文献
20.
Abstract. Ignition of a liquid layer and dust fuel layer by a detonation wave propagating in hydrogen-oxygen and acetylene-oxygen mixtures
is reported. Experiments were carried out using a shock tube equipped with optical-quality observation windows. A schlieren
system and a high-speed camera were used for measurements of ignition delay. Pressure transducers provided data necessary
for measurements of the detonation wave velocity and pressure variation within the front of the interacted detonation wave
and fuel layer. Kerosene, nitroglycerin and PETN were used as fuels. Investigation shows that the layer of liquid fuel can
be efficiently ignited by detonation wave. It was found that the ignition delay of the fuel layer depends mostly on the detonation
wave velocity and sensitivity of igniting fuels, and slightly on the layer thickness.
Received 12 August 2001 / Accepted 1 July 2002 Published online 4 February 2003
Correspondence to: P. Wolanski (e-mail: wolanski@itc.pw.edu.pl)
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