Acetylene-oxygen Mixtures Research Articles

Influence of explosions of acetylene-oxygen mixtures on the impact strength and hardness of ABS-2020 plastic

An investigation was made at the Oxyacetylene Machinery Production Union into the influence of the impact strength of ABS-2020 plastic in the action of explosions of acetylene-oxygen mixtures. The investigations were made on samples produced by casting under pressure on a D3132-250 thermoplastic automatic molding machine at a molten plastic temperature of 210/sup 0/ C, a pressure of 120 MPa, and a mold temperature of 70/sup 0/C. The results obtained were used for establishment of the optimum service life expressed in the number of explosions for protective devices intended for operation under conditions of explosions of acetylene-oxygen mixtures. This paper reports on these aspects of the investigations.

Effect of composition of a combustible gas mixture on the parameters of a plane shock wave generated by an explosion in air

This article presents the results of calculations of the parameters of shock waves in air formed by the explosion of acetylene-oxygen and propane-air mixtures. The detonation wave is initiated along the plane of symmetry. It is assumed that the parameters of state of the air are described by the equation of an ideal gas with an adiabatic exponent of air. The parameters of the detonation products in the Chapman-Jouguet plane and during isentropic expansion are determined from an equilibrium thermodynamic calculation. It is determined that the total fraction and nature of the redistribution between the internal and kinetic energies in the air depend slightly on the composition of the combustible mixture.

Gasdynamic CO laser utilizing hydrogen-containing active media

The gain of a gasdynamic CO laser utilizing a hydrogen-containing mixture was calculated using generalized data on the VT and VV relaxation times of CO and H2 molecules. Deexcitation of excited carbon monoxide molecules by hydrogen atoms was taken into account. Laser emission was recorded experimentally from a CO gasdynamic laser utilizing the combustion products of an acetylene-oxygen mixture diluted with argon.

Direct initiation of spherical detonation by a hot turbulent gas jet

An experimental study to establish the basic mechanisms of transition from deflagration to spherical detonation downstream of flow obstructions has been performed. The flow obstructions consist of circular and rectangular orfice plates, multiple rectangular orifice plates and circular hole perforated plates. In order to keep the apparatus reasonably small and also to facilitate photographic observations at low initial pressures, acetylene-oxygen mixtures at equimolar composition were used throughout. The principal diagnotics were stereoscopic streak and framing schlieren photography. The apparatus consists of a spherical flame chamber connected to a cylindrical detonation chamber via an orifice plate mounted in the port-hole connecting the two chambers. The mechanism of detonation initiation is found to be due to the intense mixing of the hot combustion products with the unburned gases. Large scale eddies are found to be essential for detonation. These eddies provide the main mechanism of entrainment, and are also partially responsible for providing energy to maintain the intensity of the finer scale turbulence. When wire screens are used in conjunction with the orifice plates, the formation of detonation is facilitated, indicating that the fine scale turbulence which is produced plays a role in rapid mixing of the entrained gases inside the large scale eddies. Under critical conditions, when the initiation results from one single eddy, it appears that shock wave amplification by coherent energy release (SWACER) inside an eddy, where a gradient field of induction time due to entrainment is present, is most probable. This suggests that the minimum size of the required eddies must be at least of the order of the detonation kernel (i.e., transverse wave spacing) of the mixture. The present experimental findings that the obstructions which produce eddies of size of the order of transverse wave spacing lead readily to detonation initiation support this view.

On the measure of the relative detonation hazards of gaseous fuel-oxygen and air mixtures

The critical energy for direct initiation of spherical detonation for eight gaseous fuels (C 2 H 2 , C 2 H 4 , C 2 H 4 O, C 3 H 6 , C 2 H 6 , C 3 H 8 , CH 4 and H 2 ) have been measured using a planar detonation from a linear tube for initiation. On the basis of the minimum value of the critical energy (corresponding to about the stoichiometric composition) a dimensionless parameter D H is defined by the ratio of the minimum energy of the fuel to that of acetylene-oxygen mixture. The magnitude of D H is then used for comparing the relative detonation sensitivity of the various fuels. Based on the values of D H for fuel-oxygen mixtures, it is found that ethylene oxide with a value of D H ⋍10 is about 10 times less sensitive than acetylene (D H =1). The olefins (i.e., ethylene and propylene) having values of D H ⋍10 2 are about 100 times less sensitive than acetylene. The alkanes (i.e., propane, ethane, etc.) have values of D H ⋍10 3 with the exception of methane which is particularly insensitive with a value of D H ⋍10 5 . Hydrogen is found to be similar to the normal alkanes with a value of D H ⋍10 3 . Fuel-air mixtures in general have values of D H about 10 6 times larger than the corresponding values for the same fuel with pure oxygen. The relative sensitivities of the various fuels remain the same for fuel-air mixtures as in the case of fuel-oxygen mixtures.

The reduction of nitric oxide during the combustion of hydrocarbons: Methodology for a rational mechanism

Mixtures of nitric oxide, oxygen and acetylene were heated to temperatures in the range 1400–2600°K in a single-pulse shock tube. Reaction temperatures were estimated from measured incident shock velocities. The final product concentrations were measured via gas chromatographic techniques. The analytical data were then reduced to mole fraction profiles of products vs. reaction temperature for dwell times (0.35–1.25 ms) under reflected shock conditions. A systematic procedure was developed for listing all possible reactions which could occur between pairs of reagents included within a specified list of molecules and molecular fragments. A set of criteria was formulated for eliminating from this very large set of possible reactions all those which were significantly less important than the dominant steps retained in the final mechanism. Computer modeling with the proposed mechanism led to good agreement with the experimental concentration profiles. This was done first for acetyleneoxygen mixtures, and then extended to the acetylenenitricoxideoxygen system. That the computer generated mole fraction profiles for mixtures containing NO compared well with the experimental results serves to establish the key reactions which reduce the pollutant NO when the exhaust gases from internal combustion engines are mixed (at about 1500°K) with hydro-carbons and air. The systematic procedure proposed in this report for developing mechanisms for complex systems is applicable to most gaseous reactions.

A comparison of the critical energies for direct initiation of spherical detonations in acetyleneoxygen mixtures

The present paper describes some new results for the critical energy for direct initiation of detonations in acetyleneoxygen mixtures using electrical sparks. The present spark energies represent the true effective initiation energies, independent of discharge characteristics and electrode configurations and gap spacings. Comparisons with existing data from exploding wire, laser and electrical sparks, as well as initiation by firing a planar detonation in a larger volume, indicate no qualitative differences in the dependence of the critical energy on mixture composition. As far as pressure dependence is concerned, the present results agree with the previous data on laser sparks and electrical sparks. However, for exploding wire and initiation by a planar detonation, much stronger pressure dependence is obtained. A simple model is proposed for direct initiation of spherical detonation by firing a planar detonation into a larger volume. The model enables critical tube diameter data to be reduced to equivalent energies, and good agreement between the critical diameter data of Matsui and the present critical spark energies is obtained on the basis of this model.

Characteristics of a pulse in detonation spraying

1. Methods have been developed for measuring the temperature and velocity of the gas stream in detonation spraying. 2. The time dependence of these parameters has been determined for the process of detonation spraying with an acetylene-oxygen mixture. 3. Analysis of the relations obtained shows that the dynamics of particles of the material being sprayed is controlled mainly by the gas flowing out of the barrel after the end of detonation.

An experimental investigation of the direct initiation of spherical detonations

A study is described of the direct initiation, by solid explosives, of detonation waves in stoichiometric propane-oxygen diluted with nitrogen and contained in plastic balloons of between 1–2 m dia. The ignition source energies lie in the approximate range of 1–50 kJ. Quantitative information on the flow field behind the initiating blast wave, near the source, is obtained from pressure profiles given by pressure-bar gauges made of high tensile steel. Wavefront velocities are continuously monitored by a 3 cm microwave interferometer. Velocity profiles exhibit similar characteristics to those predicted by the “phenomenological” model of Lee et al. During the transition process from initiating blast wave to detonation large fluctuations are sometimes observed in the flame front velocity. This observation is not unlike the reported findings of Lee et al., Brossard and Struck, each of whom has observed, using spark initiation, a quasi-steady low velocity regime just prior to the establishment of a steady C-J wave. A simple criterion is postulated which relates the duration of the spherical blast wave flow, when its velocity is equal to the C-J velocity, and the duration of the subsonic flow behind the front in a self-sustaining C-J wave. This enables the critical weight of solid explosive to be predicted for various gaseous systems. The values predicted by the criterion are found to agree reasonably well for those determined experimentally for propane-oxygen and acetylene-oxygen mixtures.

Relation between ion creation and C 2, CH and OHformation in the combustion of hydrocarbons

In the previous paper, studies on C 2 , CH, and OH emission and ion formation in the reactionof acetylene and oxygen ignited by a strong luminous flash were described, and a sequence of chemical reactions responsible for producing the radicals and ions was proposed. The weak point of the experiments was the need to photosensitize the mixture with a small amount of nitrogen dioxide (NO 2 ), which may affect acetylene-oxygen reactions. One of the purposes of our present study was to determine the effect of the nitrogen dioxide.The results already reported were compared first with those obtained using 1-3-5 cycloheptatriene (C 7 H 8 ), the reaction of which is initiated by a flash without nitrogen dioxide. The results were then compared with those obtained when an acetylene-oxygen mixture without nitrogen dioxide is ignited by a microwave. Since no difference, at least no qualitative difference, was observed, it was proposed that nitrogen dioxide does not essentially affect emission and ion formation. Next, various hydrocarbons, other than acetylene, were examined, but no notable difference was found insofar as emission and ion formation were concerned, which was to be expected from the well-known theory that hydrocarbons generally produce acetylene during chain reactions. The present paper also reports on a vacuum ultraviolet light emitted for a short time by the reacting mixtures. This uv light has a photoelectric effect on the electrodes used in the combustion tube to detect ions, and charges them positively. It is suggested that the radical responsible for this is CO (A 1 II).

On the structure of detonation waves in gases

The structure of two-dimensional detonation waves in equimolar acetylene-oxygen mixtures was studied by a variety of optical techniques yielding instantaneous photographs of the fronts as well as records of the traces of triple wave intersections—the elementary components of the waves. The changes in the shock Mach number and in the concomitant induction time associated with a triple point collision were computed as functions of the incident angle between the triple points and the propagation velocity before collision. The results elucidate the significance of the relationship between this angle and the irregularities in the wave structure.

Calibration of Piezoelectric Pressure Probe

Plane Chapman-Jouguet detonations in equimolar acetylene-oxygen mixtures are used to calibrate piezoelectric pressure probes of high spatial and temporal resolution in the range of 1–30 atm. The output voltage of the gauges is found to be proportional to the pressure, V=αP, where α is a calibration constant particular to each probe.

Investigation of freely expanding spherical combustion waves using methods of high-speed photography

Freely expanding spherical combustion waves in acetylene-oxygen mixtures were generated in a vessel of cubic shape. The mixture was ignited by a spark discharge with the spark gap mounted in the center of the reaction vessel. The combustion processes were observed through glass windows providing a 10-cm-diam field of view. The phenomena were visualized either by means of streak self-light recording or, using the method of schlieren-interferometry, by spark photography. The events were photographed with a rotating drum camera which provided a time resolution of 0.2 μsec. By the method of schlieren-interferometry, significant information on the combustion processes was obtained. Whereas the deflagration process is characterized by an irregular cellular structure, the detonation process shows an exact discontinuity at the wave front and a regular flow pattern immediately after passage of the wave. Turbulence behind the detonation wave and instability phenomena were not observed. Taking both continuous time records and spark photographs, the history of the transition process leading from deflagration to detonation was reconstructed. A sequence of interferograms taken from subsequent stages in different experiments revealed that true transition does not occur. Only the influence of the electrode mounting and the vessel walls results in the onset of detonation.

Transverse wave structure in detonations

Transverse wave structure in detonations has been investigated using the smoked-foil technique in hydrogen-oxygen and acetylene-oxygen mixtures diluted with argon, helium or nitrogen. The experimental results may be interpreted to show that the nature of the transverse structure is not only dependent on the geometry of the detonation tube but is also dependent to some extent on the heat-capacity ratio of the explosive mixture. In particular, low-heat-capacity mixtures are shown to 1) couple more readily with the fundamental rectangular or planar modes of a rectangular tube, and 2) exhibit a more regular writing pattern during propagation. In addition, the delay to the spontaneous appearance of transverse structure during one-dimensional initiation has been measured and found to agree satisfactorily with a recent acoustic theory for the rate of growth of a transverse acoustic wave. Transverse wave spacing has been measured over a large range of dilutions and pressures in rectangular, planar, and circular tubes for both of these fuel systems, and these measured values have been compared to a very tentative finite amplitude theory based on a calculation of the shock-wave behavior during the refraction of opposing transverse interactions at their intersection. This calculation shows that the refraction behavior is particularly simple in some cases and, in addition, that the theoretical spacings bracket the experimental spacings for two different but quite reasonable assumptions concerning the extent of the reaction zone.

Shock-flame interaction in a cylindrical chamber.

is produced toward the axis of the vortex along the wall. Since the fluid carried inward cannot accumulate at the attachment points without producing an unsteady change in the flow structure, the point of attachment at one end moves to a region where the ambient pressure is lower than it is at the other end and thus establishes a steady axial flow that removes the fluid brought to the axis at the high-pressure end. In the present case, a suitably low pressure for venting in this way is found near the edge of the hole on either side of the longitudinal axis and somewhat downstream of the center of the hole. Fig. 1 Streak photograph of a cylindrical flame taken across a 2-mm-wide, diametral slit. Equimolar acetylene-oxygen mixture at an initial pressure of 100 mm Hg is used.

Direct Initiation of Cylindrical Gaseous Detonations

Experimental results on the variation of the critical energy for direct initiation of cylindrical detonation waves with mixture composition and initial pressure are reported for acetylene-oxygen mixtures.

Cylindrical Imploding Shock Waves

A technique for producing imploding cylindrical shock waves through imploding detonation waves is described. It is found that using the present method of initiation, symmetrical cylindrical imploding detonation waves can be produced in equimolar acetylene-oxygen mixtures at initial pressures above 150 mm Hg. Due to the effect of area convergence, the detonation wave becomes increasingly over-driven as it implodes towards the center. In the limit the highly overdriven detonation wave approaches a strong shock wave. Pressure measurements at different radii from the center of symmetry indicate this self-amplifying characteristic of imploding detonation waves. Close agreement between the experimentally measured detonation pressures and those calculated by the Chester-Chisnell-Whitham method is obtained.

Observations of the Structure of Spinning Detonation

Spinning detonation waves in acetylene-oxygen mixtures highly diluted with argon have been studied in circular tubes by a variety of simple photographic, electrical, and mechanical (soot inscription) techniques. The combined results of these experiments permit the deduction of a fairly detailed description of the system of shock waves, reaction zones, and contact zones which exists at the front of the spinning detonation. The outstanding feature of the observed structure is that about half of the gas near the tube wall is burned in a wave which propagates in a nearly circumferential direction through shocked, unburned gas behind the nonplanar primary shock front. The relation of this structure to that of White's ``laminar detonations'' in rectangular nozzles and to spinning detonation wave structures recently proposed by certain Russian workers is discussed.

Ion-molecule reactions in methane-oxygen and acetylene-oxygen systems

Studies of ion-molecule reactions in methane-oxygen and acetylene-oxygen mixtures show comparatively few and relatively slow reactions between the hydrocarbons and oxygen. In methane-oxygen mixtures the principal cross product ions are CH 3 O 2 + , CH 2 O + , CHO + , and CH 3 O + , the first two being formed from O 2 + and the last two from CH 4 + . In addition, CH 4 + reacts with O 2 to form CH 3 + . In acetylene-oxygen mixtures C 2 H 2 O + , CHO + , and C 2 HO + are the only cross product ions formed in significant amounts. The first two are formed from O 2 + , and the latter probably comes principally from C 2 H + . CH 2 + and C 3 H 3 + are enhanced by oxygen, but the reactions are not well established.

Propagation of spherical combustion waves

Properties of spherical detonation waves of various fueloxidizer gas mixtures have been determined. The detonations were produced in 65 cm diameter thin walled rubber balloons; gases were initially at room temperature and atmospheric pressure. Experimental data were recorded with a high-speed strip film camera. Results showed that: (1) the propagation rates of stabilized spherical detonation waves of all systems studied are similar to those measured in long tubes, (2) the induction distances of acetyleneoxygen mixtures are inversely related to the ignition energy, and (3) the combustion waves were initially overdriven regardless of the method of ignition.