Propane-oxygen flame

Figure 4. Regions of ignition, cool flames, slow oxidation with and without the pic darret in an equimolar propane-oxygen mixture. Bars on the boundaries represent experimental points, and numbers on these curves signify the duration of induction periods (in seconds). Numbered regions are defined in the text...

Flame processes have been widely used to synthesize nanosize powders of oxide materials. Chemical precursors are vaporized and then oxidized in a combustion process using a fuel/oxidant mixture such as propane/oxygen or methane/air [190]. They combine the rapid thermal decomposition of a precursor/carrier gas stream in a reduced pressure environment with thermophoretically driven deposi-... 

VIV propene to equimolar mixtures of propane + oxygen reduced the cool-flame induction period by ca. 18 % at 300 °C. Like the previous work, these results showed the importance of the conjugate alkene in the autocatalytic oxidation of propane. However, at 247 °C, the yield of cyclohexene just prior to the cool flame was < 1 % of the total products. In contrast, at temperatures above 300 °C, it becomes the major product and is formed in roughly equal amounts with hydrogen peroxide prior to a stabilized cool flame [52]. Tipper concluded that above 300 °C reaction (2) occurs to an appreciable extent until well after the initial stage of oxidation since the differential yield of the alkene (d[C H2 ]/ d [C Hj 2 ]) was > 25 % over at least a quarter of the reaction. 

Fig. 16. The pressure—temperature ignition diagram for propane—oxygen mixtures in the molar ratio 1 1. Cylindrical silica reaction vessel, volume = 30 cm. (1), (4) slow reaction (2), (5) slow reaction with pic d arret (3) normal flames (6) cool flames. (From ref. 147.)...

Notwithstanding the obstacles, however, some absorption studies of combustion processes have been made. Molecular intermediates, such as aldehydes and acids, have been identified in the slow combustion of propane . Hydroxyl radicals can be observed in the absorption spectra of several flames . The greatest success in the application of absorption spectroscopy to flame studies has been in investigations of diffusion flames. Wolfhard and Parker studied the diffusion flames in oxygen of hydrogen, ammonia, hydrocarbons and carbon monoxide. In every case they were able to observe absorption by hydroxyl radicals, and they observed also the absorption of NH in the ammonia flame (NH2 appeared in emission only). Molecular oxygen, and in suitable cases the reactants, could be detected by their absorption spectra, so that a clear picture of the structure of the diffusion flame... 

The treatment with a fuel gas-oxygen flame (propane/butane or acetylene with excess oxygen, recognizable by the blue coloration of the flame) results in a chemical and physical surface modification, also with oxidative effects. This method is particularly suitable for handycraft applications, because of its low effort and expenditures. The flame treatment time is in the range of seconds, the distance of the flame to surface should be approximately 5-10 cm. In the case of thermoplastics like polyethylene and polypropylene, care should be taken that surface melting is avoided. 

Interferences in the solid phase will increase with decreasing temperature of the flame. For example, in the air-propane and air-hydrogen flames the thermal dissociation is incomplete. The analyte may react in the flame with oxygen, hydroxyl radicals, or hydrogen to form new compounds, of which oxides are the most important. The oxide formation can be minimized in reducing conditions by increasing the carrier flow rate with respect to the oxidant flow rate. 

Slowik et al. [59] used the mass-mobility relationship to investigate the impact of fuel equivalence ratio on soot morphology produced by a propane-oxygen flame. Two types of soot particle were observed, depending on the fuel equivalence ratio. For <5 < 4, the fractal dimension of the particles was approximately 1.7 0.15. These... 

The dope is concentrated by heating under vacuum and is then dry spun through a spinneret. The green fibers are partially dehydrated in a drying column and are taken up on a collapsible reel [23-24] or further processed continuously on line [25]. They are prefired at 600-800°C and subsequently sintered at 1350 - 1500°C in a furnace or/and a propane/oxygen flame. Fiber FP is 18-20 pm in diameter whereas the Almax fiber obtained from ultrafine y-alumina powder displays a smaller diameter ( 10 pm). In both fibers, alumina is present as corundum. 

Evans CJ, Kyritsis DC Operational regimes of rich methane and propane/oxygen flames in mesoscale non-adiabatic ducts, Proc Combust Inst 32 3107—3114, 2009. 

Fig. 2 shows the spatial profiles for a stoichiometric propane/oxygen flame at 6.5 Torr. There are several salient features. First, the OH emission profile peaks higher off the burner (i.e., later in the flow) than the ground state CH profile. The O2 concentration, although not measured here, must continually decrease as a function of distance from the burner. Over this region, the temperature (measured... 

Vertical Hydrogen or propane flame in oxygen and nitrogen atmosphere Oxygen index... 

Although the existence of the NTC region and, respectively, cool flames in the oxidation of very rich methane—oxygen mixtures has not yet been demonstrated, this phenomenon was shown to take place for rich (up to [C3Fl8]/[02] = 23) propane—oxygen mixtures (Fig. 8.16) [165]. 

In a spatial structure such as a hard foam with quick-burning mixtures (H2+ air or light hydrocarbon mixtures like propane + oxygen -I- some nitrogen), fast quasidetonation processes have developed. When some hydrocarbon + air mixtures were used, flame quenching was observed [24]. No slow combustion regimes were reported [24]. 

Cool Flames. An intriguing phenomenon known as "cool" flames or oscillations appears to be intimately associated with NTC relationships. A cool flame occurs in static systems at certain compositions of hydrocarbon and oxygen mixtures over certain ranges of temperature and pressure. After an induction period of a few minutes, a pale blue flame may propagate slowly outward from the center of the reaction vessel. Depending on conditions, several such flames may be seen in succession. As many as five have been reported for propane (75) and for methyl ethyl ketone (76) six have been reported for butane (77). As many as 10 cool flames have been reported for some alkanes (60). The relationships of cool flames to other VPO domains are depicted in Figure 6. 

Propane. The VPO of propane [74-98-6] is the classic case (66,89,131—137). The low temperature oxidation (beginning at ca 300°C) readily produces oxygenated products. A prominent NTC region is encountered on raising the temperature (see Fig. 4) and cool flames and oscillations are extensively reported as compHcated functions of composition, pressure, and temperature (see Fig. 6) (96,128,138—140). There can be a marked induction period. Product distributions for propane oxidation are given in Table 1. 

Short exposure image of growth of instability on a propane-air flame enriched with oxygen. The image has been rotated 90°. (From Searby, G., Truffaut, J.M., and Joulin, G., Phys. Fluids, 13, 3270, 2001. With permission.)... 

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%. 

It is further found that the adiabatic flame temperature is approximately 1300 °C for mixtures involving inert diluents at the lower flammable limit concentration. The accuracy of this approximation is illustrated in Figure 4.19 for propane in air. This approximate relationship allows us to estimate the lower limit under a variety of conditions. Consider the resultant temperature due to combustion of a given mixture. The adiabatic flame temperature (7f ad), given by Equation (2.22) for a mixture of fuel (Xp), oxygen (Xo2) and inert diluent (Xd) originally at 7U, where all of the fuel is consumed, is... 

The required heat for the brazing cycle shall be produced by a controlled fuel gas flame. The fuel gas (e.g., acetylene, propane, or natural gas) is to be combusted with air, compressed air, or oxygen. The specific combination selected is dependent on the amount of heat required to bring the particular components to the brazing temperature in the required time. 

FIGURE 1.6 Calculated stoichiometric flame temperatures of propane and hydrogen in air and oxygen as a function of pressure. 

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