Ethylene, flame speed

The dual 20-mesh stainless steel arrester was effective in arresting flashback from all eight fnel-air mixtures tested except in some ethylene-air tests. It failed in three out of three tests where the flame speed was 4.86 m/s (15.94 ft/s) or greater. 

Fuel-pair mixtures, in soap bubbles ranging from 4 to 40 cm diameter and with no internal obstacles, produced flame speeds very close to laminar flame speeds. Cylindrical bubbles of various aspect ratios produced even lower flame speeds. For example, maximum flame speeds for ethylene of 4.2 m/s and 5.5 m/s were found in cylindrical and hemispherical bubbles, respectively (Table 4.1a). This phenomenon is attributed to reduced driving forces due to the top relief of combustion products. 

Van Wingerden and Zeeuwen (1983) demonstrated increases in flame speeds of methane, propane, ethylene, and acetylene by deploying an array of cylindrical obstacles between two plates (Table 4.3). They showed that laminar flame speed can be used as a scaling parameter for reactivity. Van Wingerden (1984) further investigated the effect of pipe-rack obstacle arrays between two plates. Ignition of an ethylene-air mixture at one edge of the apparatus resulted in a flame speed of 420 m/s and a maximum pressure of 0.7 bar. 

Measured laminar flame speeds of (a) ethylene/air, (b) n-heptane/air, (c) iso-octane/air, and (d) n-decane/air mixtures as a function of the equivalence ratio for various unburned mixture temperatures. 

Hirasawa, T., Sung, C.J., Yang, Z., Joshi, A., Wang, H., and Law, C.K., Determination of laminar flame speeds of fuel blends using digital particle image velocimetry Ethylene, M-butane, and toluene flames, Proc. Combust. Inst., 29,1427, 2002. 

Flame Studies. The effects of ethylene dibromide, bromoform, and chloroform on flame speeds of several hydrocarbons were examined. These studies were carried out with 5% molar concentration of the halogen compounds in each hydrocarbon. All the experiments were carried out under identical conditions, and the results reported in Table I are the mean of at least three separate determinations. 

Turbulence is required for the acceleration of flame front to speeds required to produce the blast overpressure associated with a VCE. In the absence of turbulence, a flash fire will occur without any appreciable overpressure, with the hazard limited to the thermal radiation impacts associated with the burning of the cloud from the ignition point back to the release source, or within the flammable range of the cloud. Flame turbulence is typically formed by the interaction between the flame front and obstacles. The blast effects produced by VCEs vary greatly and are primarily dependent on flame speed therefore, areas of confinement and congestion near the release point can influence the likelihood of a VCE. Additionally the reactivity of the material is an important consideration highly reactive materials such as ethylene oxide are much more likely to lead to a VCE than lower reactive materials such as methane. 

Gordon L. Dugger and Sheldon Heimel, Flame Speeds of Methane-Air, Propane-Air, and Ethylene-Air Mixtures at Low Initial Temperatures, Nat. Advisory Committee for Aeronautics TN 2624, Washington, D.C., February 1952, 25 pp. 

In Sheen et al. (2009), this approach was applied to the modelling of experiments for ethylene combustion. Uncertainty factors for each rate coefficient in the USC Mechanism (Wang et al. 2007) were adopted from literature evaluations such as Baulch et al. (1992, 1994) and Baulch et al. (2005), and then propagated through models for flame speed, flow reactor and ignition delay predictions. The approach was also coupled with optimisation of the input rate parameter coefficients based on... 

Fig. 5.16 Experimental data and computed 2o uncertainty bands for the laminar flame speed of ethylene-air mixtures at p = l atm. Reproduced from Sheen et al. (2009) with permission from Elsevier...

Fig. 5.26 Variation of laminar flame speed with equivalence ratio for ethylene-air flames, P = 5 atm. Left panel prior model. Right panel posterior model. The shaded bands indicate the 2o standard deviation on the model prediction uncertainty shading intensity indicates the probability density, and the actual 2a limits are indicated by the dashed lines. Reprinted from (Sheen and Wang 2011a, b) with permission from Elsevier...

A detonation occurs when the flame velocity reaches supersonic speeds above 600 m/s and generally in the 2000-2500 m/s range. Peak overpressures can be 20—100 times the initial pressure, with typical values of 20 bar. Detonation can be initiated either by use of a high explosive charge or from a deflagration wave that accelerates due to congestion and confinement. Certain chemicals are more prone to create detonations than normal hydrocarbons. These include ethylene, acetylene, and hydrogen. 

Industrial applications include pipe seals, hydraulic system seals, dampers for machinery and high speed printers, and motor lead wire insulation. The fact that the polymer contains no halogens along with certain unique compoimding techniques for flame resistance prompts the selection of ethylene-acrylic as jacketing material on certain transportation/military electrical cables, and in floor tiles. 

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