Flame Region

Such a plot of data is illustrated by Cox and Chitty [18] in Figure 10.14. The regression line favors the data in the intermittent flame region and in the plume immediately above the flame. For these data the virtual origin is 0.33 m below the burner. In the continuous... 

FIGURE 3.9 General explosion limit characteristics of stoichiometric hydrocarbon-air mixture. The dashed box denotes cool flame region. 

At first, the question of the relative importance of ROOH versus aldehydes as intermediates was much debated however, recent work indicates that the hydroperoxide step dominates. Aldehydes are quite important as fuels in the cool-flame region, but they do not lead to the important degenerate chain branching step as readily. The RO compounds form ROH species, which play no role with respect to the branching of concern. 

Roper [10] also showed that the velocity of the fuel gases is increased due to heating and that the gases leaving the burner port at temperature T() rapidly attain a constant value 7 in the flame regions controlling diffusion thus the diffusivity in the same region is... 

Tcl is center line gas temperature (K) above the flaming region at a height, z... 

The experimental setup for diode-laser sensing of combustion gases using extractive sampling techniques is shown in Fig. 24.8. The measurements were performed in the post-flame region of laminar methane-air flames at atmospheric conditions. A premixed, water-cooled, ducted flat-flame burner with a 6-centimeter diameter served as the combustion test-bed. Methane and air flows were metered with calibrated rotameters, premixed, and injected into the burner. The stoichiometry was varied between equivalence ratios of = 0.67 to... 

Fig. 6.20 Experimental particle paths in an opposed stagnation flow. A mixture of 25% methane and 75% nitrogen issues upward from the bottom porous-plate manifold and a mixture of 50% oxygen and 50% nitrogen issues downward from the top porous-plate manifold. The inlet velocity of both streams is 5.4 cm/s. Both streams are seeded with small titania particles that are illuminated to visualize the flow patterns. The upper panel shows cold nonreacting flow that is, the flame is not burning. In the lower panel, a nonpremixed flame is established between the two streams. Thermal phoresis forces the particles away from the flame zone. The fact that the flame region is flat (i.e., independent of radius) illustrates the similarity of the flow. Photographs courtesy of Prof. Tadao Takeno, Meijo University, Nagoya, Japan, and Prof. Makihito Nishioka, Tsukuba University, Tsukuba, Japan.

Garner, Long, and Temple (19), using a flow system so that large amounts of reaction products could be collected, observed a ratio of acetaldehyde to formaldehyde of about 4.5 to 1 in the oxidation of hexane at 310° C. in a stoichiometric mixture. Bailey and Norrish (2) studied the oxidation of hexane in the cool-flame region. The considerable quantities of formaldehyde in the products were presumed to arise from alkoxy-radical decomposition and a methyl radical-oxygen reaction. 

For mixtures between b and c luminescence would appear in the vessel, the temperature and pressure would show a sudden jump and there would be an audible click. This is the cool flame region, where degenerate branching becomes dominant. If not all the reactant is used up in the first cool flame... 

For initial temperatures between q and r a cool flame region exists, but, in contrast to region n, p, the overall rate must decrease with increasing temperatures since at r reaction enters the steady state region. Between q and r reaction has a negative temperature coefficient. 

Fig. XIV. 10. Ignition limits for equimolar mixtures of CjHs and O2. Limits after work of D. M. Newitt and L. S. Thornes, J, Chem. Soc., 1656, 1669 (1937). The thin dark-hatched boundary between slow combustion and explosion is the region of intense blue flames. The contoured regions designated as cool flame regions arc numbered after the number of successive cool flames which can be observed in them.

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