Flame experiment

Rate Coefficients from Flame Experiments. The most dominant ion, H30 + see Figure 1), is produced by (II) ... 

Let us reconsider the critical flame temperature criterion for extinction. Williams [25], in a review of flame extinction, reports the theoretical adiabatic flame temperatures for different fuels in counter-flow diffusion flame experiments. These temperatures decreased with the strain rate (ua0/x), and ranged from 1700 to 2300 K. However, experimental measured temperatures in the literature tended to be much lower (e.g. Williams [25] reports 1650 K for methane, 1880 K for iso-octane and 1500 K for methylmethracrylate and heptane). He concludes that 1500 50 K can represent an approximate extinction temperature for many carbon-hydrogen-oxygen fuels burning in oxygen-nitrogen mixtures without chemical inhibitors . 

It is interesting to note that stratified combustible gas mixtures can exist in tunnel-like conditions. The condition in a coal mine tunnel is an excellent example. The marsh gas (methane) is lighter than air and accumulates at the ceiling. Thus a stratified air-methane mixture exists. Experiments have shown that under the conditions described the flame propagation rate is very much faster than the stoichiometric laminar flame speed. In laboratory experiments simulating the mine-like conditions the actual rates were found to be affected by the laboratory simulated tunnel length and depth. In effect, the expansion of the reaction products of these type laboratory experiments drives the flame front developed. The overall effect is similar in context to the soap bubble type flame experiments discussed in Section C5c. In the soap bubble flame experiment measurements, the ambient condition is about 300 K and the stoichiometric flame temperature of the flame products for most hydrocarbon fuels... 

Various kinds of information can be expected from the high pressure combustion and flame experiments Reaction kinetics data for conditions of very high collision rates. Results about combustion products obtained at high density and with the quenching action of supercritical water, without or with flame formation. Flame ignition temperatures in the high pressure aqueous phases and the ranges of stability can be determined as well as flame size, shape and perhaps temperature. Stationary diffusion flames at elevated pressures to 10 bar and to 40 bar are described in the literature [12 — 14]. 

When Pe is less than about 46, heat loss effects on Umay be appreciable. If an analogy is made with turbulent flames using a turbulence Peclet number defined by Pe = Urd/aT, where ar 0.058RciZ/ [21, 22], it is readily shown that Pe is substantially above 46 for all of the present turbulent flame experiments. The influence of heat loss is therefore not likely a contributor to the bending effect exhibited in Fig. 15.4. 

The opposed-flow situation has been used very successfully to study the structure of flames as a function of fluid mechanical strain rates. Figure 6.20 illustrates one such flame experiment. Here flow issues from two porous plates in an opposed-flow configuration. The velocity leaving each plate is uniform across the plate surface and the temperature and composition is also uniform. One flow stream is air and the other contains methane, and both streams are seeded with small titania particles. By illuminating the flow with a sheet of laser light, we see streak lines that are formed by the particles as they follow the flow. In the... 

Gedanken Flame Experiment. In order to illustrate how the problems caused by the requirements of temporal and spatial resolution and geometric and physical complexity are translated into computational cost, we have chosen to analyze a gedanken flame experiment. Consider a closed tube one meter long which contains a combustible gas mixture. We wish to calculate how the physical properties such as temperature, species densities, and position of the flame front change after the mixture is ignited at one end. The burning gas can be described, we assume, by a chemical kinetics reaction rate scheme which involves some tens of species and hundreds of chemical reactions, some of which are "stiff."... 

Important Scales in Gedanken Flame Experiment Timescales Spacescales... 

Using the information discussed so far, we can now return to the gedanken flame experiment with the idea of considering modified numerical methods in order to reduce the computational cost. The goal is to calculate the propagation of a flame front across a one-meter tube using a one-dimensional geometry with a fixed detailed chemical reaction rate scheme. 

Reference has already been made to the diffusion flame experiments of Polanyi and his co-workers. Some less well-known results [2, 52, 53] obtained with the same method demonstrated that KX is formed from K + X2... 

FIGURE 5.1. Schematic diagram of a typical laminar-flame experiment. 

In all these laminar-flame experiments, the combustion wave propagates at a definite velocity that empirically depends on the pressure, temperature, and composition of the initial combustible mixture. Our primary objective in this chapter is to predict this burning velocity. In Section 5.1.2 a simple physical picture of the deflagration wave is presented, leading to a crude estimate of the burning velocity. The discussion, which is similar to that of Landau and Lifshitz [3], illustrates the essential mechanism involved. 

Excess air (fuel lean conditions) and high temperatures favor the conversion of HCl into CI2. The formation of CI2 can then lead to the production of chlorinated hydrocarbons, as seen in flame experiments. 

Emission has been observed [364] from various electronic states of BaCl (C n, A n) from Ba + ONCl and of CaCl (B S, A Yi) from Ca + ONCl in a low pressure diffusion flame experiment. No individual vibrational bands were resolved. For Ca 4- ONCl, the population of the CaCl electronic states was in the order X> A>B, reflecting the increasing energy of the state. However, for Ba + ONCl, the ordering isX>C>A. 

A surrounding coaxial nitrogen flow is sometimes necessary in opposed flame experiments to prevent stabilization of a flame in the shear layer between the... 

Korusoy, E., and J.H. Whitelaw. 2001. Opposed jets with small separations and their implications for the extinction of opposed flames. Experiments Fluids 31 111-... 

Wang, C., and Barlow, R. S. "Spatial Resolution Effects on the Measurement of Scalar Variance and Scalar Gradient in Turbulent Nonpremixed Jet Flames." Experiments in Fluids 44 (2008) 633-45. 

It will be noted from Table 13 that single temperature rate coefficients are listed and not Arrhenius parameters. The latter are not readily derived from the original type of experiments, which are not suitable for the measurement of temperature coefficients because of the difficulty of assessing the variations of quantities such as the diffusion coefficient and the limit of detectability of sodium atoms. An interesting competitive method has been developed to study Na and K atom reactions which overcomes these difficulties [146]. The alkali metal atoms were reacted in diffusion flame experiments with pairs of organic halides. By labelling one of the halides with Cl and by analysing for the total concentration and... 

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