Measured flame

Other examples of government and military applications of laser-based profilometry include the evaluation of rocket thruster nozzles to locate and measure flame erosion remote inspection of hypervelocity test track and the measurement of sludge deposits on tube internal surfaces. 

Low energy ion-molecule reactions have been studied in flames at temperatures between 1000° and 4000 °K. and pressures of 1 to 760 torr. Reactions of ions derived from hydrocarbons have been most widely investigated, and mechanisms developed account for most of the ions observed mass spectrometrically. Rate constants of many of the reactions can be determined. Emphasis is on the use of flames as media in which reaction rate coefficients can be measured. Flames provide environments in which reactions of such species as metallic and halide additive ions may also be studied many interpretations of these studies, however, are at present speculative. Brief indications of the production, recombination, and diffusion of ions in flames are also provided. 

The chronology of the most remarkable contributions to combustion in the early stages of its development is as follows. In 1815, Sir Humphry Davy developed the miner s safety lamp. In 1826, Michael Faraday gave a series of lectures and wrote The Chemical History of Candle. In 1855, Robert Bunsen developed his premixed gas burner and measured flame temperatures and flame speed. Francois-Ernest Mallard and Emile Le Chatelier studied flame propagation and proposed the first flame structure theory in 1883. At the same time, the first evidence of detonation was discovered in 1879-1881 by Marcellin Berthelot and Paul Vieille this was immediately confirmed in 1881 by Mallard and Le Chatelier. In 1899-1905, David Chapman and Emile Jouguet developed the theory of deflagration and detonation and calculated the speed of detonation. In 1900, Paul Vieille provided the physical explanation of detonation... 

A theory, termed as the back-pressure drive flame propagation theory, has been proposed to account for the measured flame speeds [12]. This theory gives the momentum flux conservation on the axis of rotation in the form of... 

An efficient flame retardant effect was demonstrated with 2-mil zinc coatings on polyphenylene oxide-polystyrene blends (Notyl) by Nelson (21). The action may relate to enhanced char formation by chemistry specific to this blend. However, other metal coatings on some other polymers also appeared to contribute a measurable flame retardant effect. 

Air Products, a manufacture of latex binders, has completed a comprehensive study of flame retardants for latex binder systems. This study evaluates the inherent flammability of the major polymer types used as nonwovens binders. In addition, 18 of the most common flame retardants from several classes of materials were evaluated on polyester and rayon substrates. Two of the most widely recognized and stringent small scale tests, the NFPA 701 vertical burn test and the MVSS-302 horizontal burn test, are employed to measure flame retardancy of a latex binder-flame retardant system. Quantitative results of the study indicate clear-cut choices of latex binders for flame retardant nonwoven substrates, as well as the most effective binder-flame retardant combinations available. 

Quintiere, J.G. and Harkleroad, M.F., New concepts for measuring flame spread properties, in Fire Safety Science and Engineering, ASTM STP882, (ed. T.-Z. Harmathy), American Society for Testing and Materials, Philadelphia, Pennsylvania, 1985, p. 239. 

Quintiere, J.G. and Harkleroad, M., New Concepts for Measuring Flame Spread Properties, NBSIR 84-2943, National Bureau of Standards, Gaithersburg, Maryland, 1984. 

Various approaches to measuring flame temperature are well described in Gaydon s book on flames (see Appendix C). The best methods are spectroscopic rather than those which use thermocouples. The sodium line reversal method is perhaps the easiest. Sodium is added to the flame and the sodium D lines viewed against a bright continuum source (e g. a hot carbon tube). When the flame is cooler than the source the lines appear dark because of absorption. When the flame is hotter than the tube, the bright lines stand out in emission. The current to the tube, which will have been precalibrated for temperature readings by viewing the tube with an optical pyrometer, is adjusted until the lines cannot be seen. At this reversal point, the flame and tube temperature should be equal. 

A list of substances which have been used or considered to support decomposition flames is shown in Table I. Almost all of these substances have been studied at one time or another to provide fundamental information for the evaluation of the theory of flame propagation. As previously mentioned, the ozone decomposition has proved most useful as the basis of a flame which is amenable to both theoretical and experimental study. The NO decomposition flame provided a situation where a clear-cut prediction was made possible by flame theory (P2). On the basis of a flame calculation it was predicted that a strong preheat would permit the stabilization of this flame at a measurable flame velocity, since it was known that a flame would not propagate into the gas at room temperature. Subsequent experimental work confirmed the prediction by stabilizing a flame with approximately the predicted value. This places a great deal of... 

We mentioned in 1.3 the agreement achieved between the calculated and measured flame velocity this agreement is pertinent to mixtures containing 50-55% H2 in which the flame propagates as a solid front. 

Tourin, R.H., Spectroscopic Gas Temperature Measurement, Elsevier Publishing Co., Amsterdam, 1966. Gaydon, A.G. and Wolfhard, H.G., The spectrum-line reversal method of measuring flame temperature, Proc. Phys. Soc. (London), 65A, 19, 1954. 

In the ASTM E84 25-foot tunnel furnace test (34) for measuring flame spread of building materials, an igniting pilot flame is applied to the underside of a horizontally mounted specimen. The flame heats the combustible material to pyrolysis, and the flammable gases given off are ignited by the pilot flame. 

All boiler temperatures were measured just prior to and after the collection of the coal samples and their respective fly ashes, since it was physically impractical to collect the samples and measure the temperatures at the same times. In all cases, the temperatures remained essentially constant. An optical pyrometer was used to measure flame temperatures, and water-cooled jacketed thermocouples were used to monitor the boiler temperatures. The wall effects on the temperature measurements were minimized by insertion of the thermocouple into the boiler until temperatures remained constant with distance upon further insertion of the thermocouple into the boiler. 

Laser light-scattering techniques for measuring flame gas properties have advanced to the stage where they now can be employed to determine key flow and combustion field variables. 

Finally, from the measured flame temperature, we conclude that thermodynamic equilibrium is attained in the deflagration products. 

All the assumptions of Section 1.3 underlie the formulation. Assumption 1 deserves special mention because buoyancy forces on the hotter, less dense gas in the region of the flame often distort the shape of the flame sheet. A Froude number, Fr = v l(ag) (where g denotes the acceleration of gravity), measures the relative importance of inertial and buoyant forces. If Fr is sufficiently small (for example, Fr Ap/p, where Ap is a representative density difference and p a mean density), then the flame heights are controlled by buoyancy. Correlations of measured flame heights in the form hja Fr , where h is the flame height and < n are available for b 00 under buoyancy-influenced conditions with negligible viscous forces [9]-[ll]. The result of equation (26), namely, hja vajD = Pe, is a Peclet-number (Pe) dependence that cannot be correlated with Fr and that... 

The linear velocity of the probe tip (1 msec" ) is low compared with the gas velocity, so that this distance must be measured in the direction of gas flow, and the full width of the spike can correspond only to the passage of 10 X 10 m of ionized gas over the probe. A crystallite of KCl with the observed diameter, if volatilized at 1 atm and 2500 K (the measured flame temperature) would produce a vapor sphere of 10" m radius or a cylinder 10 X 10" m long and 4.5 X 10" m in diameter. This suggests that the spikes are indeed caused by a trail of vapor left as the particle evaporates. 

A similar flat flame technique—one that does not require a heat loss correction—is the so-called opposed jet system. This approach to measuring flame speeds was introduced to determine the effect of flame stretch on the measured laminar flame velocity. The concept of stretch was introduced in attempts to understand the effects of turbulence on the mass burning rate of premixed systems. (This subject is considered in more detail in Section 4.E.) The technique uses two... 

The interpretation of measured flame profiles by means of the continuity equations may be approached in one of two ways. The direct experimental approach involves the use of the measured profiles to calculate overall fluxes, reaction rates, and hence rate coefficients. Its successful application depends on the ability to measure the relevant profiles, including concentrations of intermediate products. This is not always possible. In addition, the overall fluxes in the early part of the reaction zone may involve large diffusion contributions, and these depend in turn on the slopes of the measured profiles. Thus accuracy may suffer. The lining up on the distance axis of profiles measured by different methods is also a problem, and, in quantitative terms, factor-of-two accuracy is probably about the best that may normally be expected from this approach at the position of maximum rate. Nevertheless, examination of the concentration dependence of reaction rates in flames may still provide useful preliminary information about the nature of the controlling elementary processes [119—121]. Some problems associated with flame profile measurements and their interpretation have been discussed by Dixon-Lewis and Isles [124]. Radical recombination rates in the immediate post-combustion zones of flames are capable of measurement with somewhat h her precision than above. 

More revealing in relation to the comparative lack of reactivity of nitric oxide are the observations of Wolfhard and Parker on H2 + NO2 flames. Here nitric oxide is found strongly in absorption in the burnt gas of both rich and lean flames, showing that it does not play a major part in the reaction. This conclusion is supported by measurement of the flame temperature of the stoichiometric mixture for H2 + 5NO2 = H2O + 5N2 [286]. Theoretically this should be 2890 K if the stoichiometry is as quoted. The measured flame temperature by line reversal was 1780 K. 

The rates of the last two reactions were obtained by partial equilibrium assumptions, while the rates of the first two reactions were tuned to reproduce both the measured flame speed and the observed CO to H2... 

H.C. Gupta, R.L. Steinberger and F.V. Bracco, Combustion in a Divided Chamber, Stratified Charge, Reciprocating Engine Initial Comparisons of Calculated and Measured Flame Propagation, Comb. Sci. Tech. 22 (1980) 27. 

The equilibrium data of Sugden and co-workers (1, 2) are likely to contain significant errors, since the dissociation constants were calculated with OH concentrations determined from measured flame temperatures and known gas compositions. It is now well established (8, 9) that flame radical concentrations vary greatly with the distance from the reaction zone of the flame. The dissociation pressure data of Johnston and Ditmars and Johnston (see LiOH(t) table) show excessive drifts which usually are indications of nonequilibrium measurements. However, even the remaining flame work (3- ) and vapor pressure data still show a scatter of over 3 kcal mol in AjH (298.15 K) of LiOH(g). Cotton and Jenkins (4) investigated the other alkali metal hydroxides, and their data lead to A H (298.15 K) values for these compounds which are quite consistent with JANAF data (10). On the other hand, the flame studies of McEwan and Phillips (5) as a function of temperature do not show significant drift yet, the... 

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