Acetylene-oxygen mixtures

A safe method for demonstrating explosive combustion of acetylene-oxygen mixtures in bubbles is described. 

Baum et al (Ref 3), besides giving on p 241 Table 52 which deals with influence of inert gases Ar N2 on deton vel of 2H2+O2 mixts, discuss on p 242 the results of Dixon s work on increase of deton vel of 2H2+O2 fr°m 282/m/sec to 2872 when the initial pressure was increased from 760 mm to 1500him Hg They also state that a much greater increase in vel can be achieved if pressures are increased much higher. For example, LeChatelier determined that increase of pressure of acetylene-oxygen mixtures from 5 to 30 atm, increased deton vel from 1000 to 1600 m /sec... 

Deton vels measured by this method agreed with values obtained from measurements in tubes by std techniques. For instance, the mixts contg 12.5% GjHj developed a deton vel of 1920 m/sec and multiple reflected waves were clearly observed (See also Acetylene-Oxygen Mixtures)... 

Figure 6. Relation of detonation velocity of acetylene-oxygen mixtures at reduced pressures to mixture ratio...

Shchelkin K. I., et al. (1947). Measurements of normal velocities of acetylene-oxygen mixture flame. ZhETF, 17, 1397 (in Russian). 

In the detonation gun technique fixed amounts of powder are accelerated by successive explosions of an acetylene-oxygen mixture. This allows velocities of the order 750 m s and temperatures of the order of 4000 °C to be achieved leading to deposits of excellent bond strength but with some porosity. 

Flashback is more likely with an acetylene-oxygen mixture than with any of the other fuel-oxidant combinations in common use. Flame propagation in this system is at 1130cm/sec. This imposes severe limitations on the use of acetylene and oxygen with premixed burners. The relatively low flame propagation rate of nitrous oxide and acetylene (180cm/sec) is a definite advantage for the system. 

Figure 1 shows the chemical equilibrium time as a function of pressure for different states on the isentropic curve of the products of explosion at a constant volume of an acetylene-oxygen mixture (T = 298 K and p = 0.1 MPa). Line 1 represents calculations by formula (18) while points 2... 

Fig. 1 Equilibration time as a function of pressure on the expansion isentropic curve for explosion products), of a stoichiometric acetylene-oxygen mixture.

Figures 2 and 3 demonstrate calculations of the chemical-equilibration process in the detonation products of a stoichiometric acetylene-oxygen mixture at T = 3160 K and density equal to 0.11 kg/m (this point lies on the isentropic line passing through the C3 point of detonation in a mixture at the initial pressure 0.1 MPa and temperature 298 K). As seen from the figures at the first state CO2 forms by reaction CO-I-OH— C02+H since CO and OH are in superequilibrium concentrations. This increases rapidly the hydrogen atom concentration (Fig. 2) so that it reaches a superequilibrium value and then drops to the equilibrium level. Concentrations of the components involved in all the bimolecular reactions satisfy the detailed balance conditions after 1 fis (Fig. 3). At later states, recombination reactions with he rate limiting step CO-j-O-l-M—> C02+M start to be prevailing.

Now we consider at what conditions inequality (9) holds for expansion of a spherical volume (with the initial radius r ) of the products formed after explosion of an acetylene-oxygen mixture. The gasdynamic calculations were performed in Lagrangian coordinates employing the conservative difference... 

Fig. 9 Relative deviations of water and carbon dioxide concentrations daring expansion of the detonation products of an acetylene-oxygen mixture.

Table 1 Initial conditions, computed detonation, and reflected shock properties for the nominal stoichiometric acetylene-oxygen mixtures used in the experiments.

Experiments were carried out at McGill University with stoichiometric acetylene-oxygen mixtures at 200-250 Torr initial pressure. Detonations were initiated by exploding wires in three separate facilities tubes 0.47 - 2.28 m long and 50 mm in diameter a cylinder 30.7 mm thick and 287 mm in diameter and a hemisphere 102 mm in radius. 

Experiments were also performed in a hemispherical vessel 102 mm in radius with a stoichiometric acetylene-oxygen mixture. Experimen-... 

HOT CHEMI5TRY The smallest alkyne is acetylene (HC=CH). It is a gas and its most common use is for welding. An acetylene/oxygen mixture burns at the very high temperature of3200 °C (5800 °F). 

Acetylene burns in air with an intensely hot, luminous, and smoky flame. The ignition temperatures of acetylene and of acetylene-air and acetylene-oxygen mixtures vary according to composition, initial pressure, initial temperature, and water vapor content. As a typical example, an air mixture containing 30 percent acetylene by volume at atmospheric pressure can be ignited at about 581 °F (305°C). The flammable limits of acetylene-air and acetylene-oxygen mixtures similarly depend on initial pressure, temperature, and water vapor content. In air at atmospheric pressure, the upper flammable limit is about 80 percent acetylene by volume and the lower limit is 2.5 percent acetylene. Some references list the upper flammable limit as 100 percent, which is due to the de-... 

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