Combustible gas mixtures

Each vault housing a pressure-limiting, pressure-relief, or pressure-regulating station shall be examined to determine its condition each time the equipment is examined and tested in accordance with para. GR-5.23.3. For any vault which personnel enter, the atmosphere shall be tested for combustible gas. If the atmosphere is hazardous, the cause shall be determined. The vault shall be examined for adequate ventilation. The condition of the vault covers shall be carefully examined for hazards. Unsatisfactory conditions disclosed shall be corrected. No welding maybe done if a combustible gas mixture is present. Maintenance work performed in the vault shall be in accordance with procedures developed per para. GR-5.23.3, with particular consideration given to the monitoring of the atmosphere and safety protection for personnel in the vault. 

Prior to welding in or around a structure or area containing gas facilities, a thorough check shall be made to determine the possible presence of a combustible gas mixture. Welding shall begin only when safe conditions are indicated. 

It is interesting to note that stratified combustible gas mixtures can exist in tunnel-like conditions. The condition in a coal mine tunnel is an excellent example. The marsh gas (methane) is lighter than air and accumulates at the ceiling. Thus a stratified air-methane mixture exists. Experiments have shown that under the conditions described the flame propagation rate is very much faster than the stoichiometric laminar flame speed. In laboratory experiments simulating the mine-like conditions the actual rates were found to be affected by the laboratory simulated tunnel length and depth. In effect, the expansion of the reaction products of these type laboratory experiments drives the flame front developed. The overall effect is similar in context to the soap bubble type flame experiments discussed in Section C5c. In the soap bubble flame experiment measurements, the ambient condition is about 300 K and the stoichiometric flame temperature of the flame products for most hydrocarbon fuels... 

The practical utility of the coupled assumptions of unit Lewis number and a single, over-all reaction step in complex reaction processes is unknown. The use of relations derivable from Equation 18, in conjunction with an experimental study, should help in providing some insight concerning the utility of these coupled approximations for representative combustible gas mixtures. 

Flame atomisation. A burner is fed with a combustible gas mixture and constructed in a robust fashion to resist possible explosions of the gas (Fig. 14.8). The flame, which has a rectangular base of approximately 10 cm by 1 mm is aligned with the optical axis of the instrument. The sample is aspirated by the Venturi effect into the mixture of combustible gases feeding the flame. 

Let us turn to Ya.B. s paper on ignition of a combustible gas mixture by a heated wall (18). By the time this paper was written, N. N. Semenov and D. A. Frank-Kamenetskii had already done work on gas ignition in closed vessels under a variety of assumptions. In N. N. Semenov s work the gas was assumed to be ideally mixed and the temperature of the gas in the vessel to be constant. D. A. Frank-Kamenetskii considered a gas at rest, so that heat transfer occurred only through molecular thermal conduction. 

Gedanken Flame Experiment. In order to illustrate how the problems caused by the requirements of temporal and spatial resolution and geometric and physical complexity are translated into computational cost, we have chosen to analyze a gedanken flame experiment. Consider a closed tube one meter long which contains a combustible gas mixture. We wish to calculate how the physical properties such as temperature, species densities, and position of the flame front change after the mixture is ignited at one end. The burning gas can be described, we assume, by a chemical kinetics reaction rate scheme which involves some tens of species and hundreds of chemical reactions, some of which are "stiff."... 

The present paper provides initial results for selected CO and NO transitions in combustion gas mixtures. 

Sintered metals show a strong correlation between open porosity and effective gap. (The effective gap weS of a flameproof component is the highest MESG (Maximum Experimental Safe Gap) value of combustible gas mixtures (see Section 1.2.2), for which that component ensures flameproofness. For gas mixtures with MESG < wen, flame transmission occurs.) (see [19]). 

Hydrocarbon molecules are abundant constituents of planetary atmospheres and major compounds in combustible gas mixtures and in fusion edge plasmas [7-11]. Methane is the simplest of these hydrocarbon molecules. Acetylene, C2H2, is the simplest hydrocarbon molecule that contains 2 carbon atoms. Thus absolute total and partial photon [24-27] and electron [15,28-34] ionization cross-sections and nascent fragment ion energy distributions [19,20,28,36-40] have been studied extensively for these molecules. For the deuterated methane molecule electron impact ionization and dissociative ionization cross-sections were determined for the CD (x=l—4) molecule and radicals applying a fast neutral beam technique [41]. Electron impact total ionization cross-sections have been determined also theoretically applying the BEB (Binary-Encounter-Bethe) model [42], the DM (Deutsch-Mark) method [43] and the JK (Jain-Khare) method [44], Partial electron impact ionization cross-sections were calculated for methane [45,46] as well as total electron impact cross-sections for various CH radicals [47]. The dissocia-... 

Using our experimental activity data for Na20 in glass, we have modeled the effect of a typical combustion gas mixture on alkali vaporization ( ). For this purpose we have acquired, and adapted to our computers, a code known as SOLGASMIX (7 ) which is unique in its ability to deal with non-ideal solution multicomponent heterogeneous equilibria. Previous attempts to model this type of problem have been limited to ideal solution assumptions ( ). As is demonstrated in Table III, if solution non-ideality is neglected, drastic errors result in the prediction of alkali vapor transport processes. Table III and Figure 21 summarize the predicted alkali species partial pressures. The thermodynamic data base was constructed mainly from the JANAF (36) compilation. Additional details of this study will be presented elsewhere. 

It was shown in Section 2.2 that the downstream Mach number is unity for Chapman-Jouguet waves. When interpreted correctly, this result applies to any combustible gas mixture. However, a possible source of ambiguity for multicomponent systems is the fact that more than one sound speed a can be defined. Since there are iV - - 2 independent thermodynamic variables in an AT-component gas mixture, N parameters besides s must be specified as constants in computing dp/dp to evaluate... 

The burning velocity Vq can be related to this wave thickness as follows. The mass of combustible material per unit area per second flowing into the wave is PqVq, where po is the density of the initial combustible gas mixture. The deflagration wave consumes these reactants at a rate wd (mass per unit area per second). Hence mass conservation implies that PqVq = wd, which, in conjunction with equation (1), yields... 

In many gases, Le is very nearly unity it is often slightly less than unity in combustible gas mixtures. The approximation Le = 1 is frequently helpful in theoretical combustion analyses. However, small departures of Le from unity often can produce new phenomena in combustion. Therefore, a number of studies have been made of influences of the value of Le. 

Calculate the gross heating value in Btu/lbmol for a combustible gas mixture of 75 mol % methane, 10 mol % propane, and 15 mol % n-butane. The following gross heating value data are available ... 

Numerical evaluations then give Sf > 0 for real combustible gas mixtures (with the possible exception of fuel-lean mixtures having hydrogen as the fuel) [38], [122], [126]. On the other hand, the quantity -I- 1) 2- relevant to the burning velocity with respect... 

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