Flames ethane-oxygen

Fig. 10.1. Experimental and theoretical concentration profiles for an ethane/oxygen flame [10.3, first Ref.] (Copyright 1982 by Scientific American, Inc.. All rights reserved)...

Formaldehyde, in sufficient quantities, can suppress cool-flame formation. Jost (27) presents evidence indicating that cool flames are a form of branched-chain explosions. It has been suggested that the cool-flame reaction is quenched by its own reaction product, formaldehyde, and arrested short of complete release of chemical enthalpy. This seems unlikely, however, because in systems exhibiting multiple cool flames the concentration of formaldehyde after the first cool flame does not drop in some cases it increases, and yet does not suppress subsequent cool flames. Bardwell (5), and Bard well and Hinshelwood (4) explain cool flame phenomena by a modified theory of Salnikov. This thermal theory is further supported by the results of Knox and Norrish (30) in the ethane-oxygen system. The key intermediate is presumed to be a peroxide by Bardwell and Hinshelwood (4). Formaldehyde is considered an inert, stable product with little effect on the reaction. 

Combustion occurs with a large number of intermediate steps and even simple processes, such as the ones listed in Table 10.1, occur through dozens of coupled elementary reactions. With computer simulations it is possible to describe the interaction between the reactions, and concentration profiles can be calculated. In order to perform the computer calculations it is necessary to know the rate constants for the individual elementary reactions. Comparisons between theory and experiments are best made for a flat, premixed flame, which in its central part can be considered to have only onedimensional (vertical) variation, allowing computer calculations to be performed comparatively easily. The most important reactions are included in the computer description. In Fig. 10.1 experimental and theoretically calculated concentration curves are given for the case of low-pressure ethane/ oxygen combustion. As examples of important elementary processes we give the reactions... 

Transient computations of methane, ethane, and propane gas-jet diffusion flames in Ig and Oy have been performed using the numerical code developed by Katta [30,46], with a detailed reaction mechanism [47,48] (33 species and 112 elementary steps) for these fuels and a simple radiation heat-loss model [49], for the high fuel-flow condition. The results for methane and ethane can be obtained from earlier studies [44,45]. For propane. Figure 8.1.5 shows the calculated flame structure in Ig and Og. The variables on the right half include, velocity vectors (v), isotherms (T), total heat-release rate ( j), and the local equivalence ratio (( locai) while on the left half the total molar flux vectors of atomic hydrogen (M ), oxygen mole fraction oxygen consumption rate... 

Two GC columns Porapak Q (for C02 and water analyses) and Molecular sieve 5A (hydrogen, oxygen, and CO) were used with two thermal conductivity detectors and another GC column with modified y-Al203 (methane, ethane, ethene, propane, propene, and C4 hydrocarbons) was used with a flame ionisation detector. Carbon and oxygen balances were within 100+5%. 

Acetylene is by far the most important commercial alkyne. Acetylene is an important industrial feedstock, but its largest use is as the fuel for the oxyacetylene welding torch. Acetylene is a colorless, foul-smelling gas that burns in air with a yellow, sooty flame. When the flame is supplied with pure oxygen, however, the color turns to light blue, and the flame temperature increases dramatically. A comparison of the heat of combustion for acetylene with those of ethene and ethane shows why this gas makes an excellent fuel for a high-temperature flame. 

Fig. 35. The effect of ethane addition on the cool-flame oxidation of acetaldehyde in a static system [70]. (a) Pressure—time plot for the cool-flame oxidation of acetaldehyde. Total pressure of a 1 1 acetaldehyde—oxygen mixture = 73 torr. Temperature = 230 °C. (b) As for (a) but with 10.9 torr of ethane present.

The composition and temperature profiles in low-pressure fuel-rich flames of ethylene oxide have been studied by Bradley et al. [65]. The major products were carbon monoxide, hydrogen, ethylene, methane, acetylene, butadiene and vinylacetylene, with traces of propene and propane. The unsaturated products were formed marginally later than the others, and ethane showed a maximum which coincided with the almost complete removal of fuel and oxygen. Acetylene and vinylacetylene continued to increase above the flame, although other products remained constant. 

The major part of diamond film production is actually covered by the CVD procedures presented in Section 6.3.1. Still there are a few other methods worth mentioning that suit to the generation of diamond films as well. These include, for instance, the flame combustion method. The respective apparatus essentially consists of a modified welding torch burning hydrocarbons at normal pressure (Figure 6.22). The carbon source most commonly applied here is acetylene, but the combustion of ethane, methane, ethylene, or methanol yields diamond films as well. The gas current is mixed with oxygen to support the combustion, but for being rich in hydrocarbon, the mixture does not burn up, and molecules of hydrocarbon still exist in the deposition zone. 

A great variety of organic combustion products have been identified (Schumacher et al., 1977 Junk and Ford, 1980 Hawthorne et al., 1988). The mechanisms of the reaction of oxygen with combustible species are, however, very poorly understood. Even such a simple fuel molecule as methane has very complex behavior during combustion. The methyl free radical formed during the initiation step has a number of possible fates including recombination to form ethane (Equation 4.68), common in fuel-rich flames ... 

In these lean flames the hydrocarbon undergoes initial attack by hydroxyl radical with the formation of a radical C H2 +i. Since hydrocarbon radicals higher than ethane are thermally unstable, methyl radical is usually split off forming the next lower molecular weight olefin. Complex radicals may fission into an intermediate-weight radical and an olefin. It seems probable, however, that the thermal destruction of the complex hydrocarbon radicals is sufficiently rapid so that the major oxidizing step is always connected with methyl radical. The principal evidence in favor of this viewpoint is the absence of oxygenated hydrocarbons (alco-... 

Dimethoxyethane (Ethylene Glycol Dimethyl Ether or Monoglyme). Because it is miscible with water, 1,2-dimethoxyethane is a useful alternative to solvents such as dioxane and tetrahydrofuran, which may be more hazardous. 1,2-Dimethoxy-ethane is flammable and should not be handled near an open flame. On long exposure of 1,2-dimethoxyethane to light and oxygen, explosive peroxides may form. 

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