Weak ignition

The results in Tables 4. la and 4. lb demonstrate that in the absence of obstacles, the highest flame speed observed was 84 m/s, and it was accompanied by an overpressure of 60 mbar for hydrogen-air in a 10-m radius balloon (Schneider and Pfortner 1981). For all other fuels, flame speeds were below 40 m/s and corresponding overpressures were below 35 mbar. Hence, weak ignition of an unconfined... 

Figure 8.4.5 presents the streak, direct photograph illustrating the stages of transition to detonation after a weak ignition and flame acceleration phase. Four main regions may be identified ... 

H.Wells, "Coal, Coke and Coal Chemicals," McGraw-Hill, NY (1950) 4)Kirk St Othmer 6, (1951), 899 (Coke as a fuel) 5)H.Gesner St H.R.Zbinden, SchweizVerGas - und Wasser-fachMonatsBull 32, 45-52 (1952) St CA 47, 7196 (1953) (Tests with coke dusts have shown that it is practically impossible to ignite their mixts with air. A weak ignition was observed only once in 15 tests) 6)W.Gluud, "Handbuch der ICokerei, K.Knapp, Diisseldorf (1953) 7)0. 

When long induction periods are necessary, weak ignition sources can initiate the explosion, such as light, wall effects, tar deposits, catalyst deposits on the wall, NC13 decomposition flame (refs. 5,9). 

The explosion of an unconfined hydrogen gas doud in the presence of a weak ignition source was never observed to have turned into a detonation [45]. The ignition energy required for a direct detonation can only be provided by either an intensive turbulent hot gas jet or by an explosive. For a stoichiometric mixture, the minimum energy was experimentally determined to be 4.7 kJ ( 1 g TNT). A methane-air mixture even requires... 

For special purposes (e.g., highchemcialresistance), materials of Group 1 can be lined with substances which by tiiemselves are not suitable for ceramic manufacture (for example, MgO, CaO). For example, according to Goehrens [3], one can apply to the vessel a paste made of a mixture of finely ground, weakly ignited and... 

Formula weight 277.52. Yellow material the lower the ignition temperature, the more soluble in water hygroscopic when weakly ignited, nonhygroscopic when strongly ignited. M.p. about 2000°C d 7.04. C sesquioxide structure type. 

Procedure. Alloys rich in tin. A few fine filings are treated in a micro crucible with several drops of nitric acid, evaporated, and then weakly ignited. The cold residue is treated with 1 drop buffer solution and 1 drop sodium rhodizonate. Red lead rhodizonate appears. 

The experiments [26] conducted for various combustion regimes of H2 + N2 + O2 mixtures in water-mechanical foams at water concentration of 10 kg/m have shown that even weak ignition of 2H2 + O2 contained in the foam cells initiates blast propagation with a 2,500 m/s velocity and a front pressure of 1.0-1.5 MPa. When the mixture is diluted to 2H2 + O2 + N2, the explosive front velocity reduces to 800-500 m/s. The velocity reduction has been recorded with the same mixture composition but with reduced the bubble size, i.e. with an increase of the heat transfer surface. 

Indirect initiation by a weak ignition, flame acceleration and DDT. 

Processes resulting from combustion initiated by a weak igniter contain complicated interactions between turbulent flows and chemical reactions. Simulation of such processes requires detailed calculations of non-stationary turbulent compressible reactive flows in three-dimensional space. 

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