摘要:

It is generally assumed in this work, as elsewhere, that the mass diffusion coefficient has an Arrhenius temperature dependence. This allows a combustion wave propagated by thermal conduction to develop similar to more conventional combustion systems. It is found that for realistic systems the problem must involve a three length scale analysis. Similar to the classic theory on premixed, gas-phase flames, the largest scale is identified with thermal conduction and a “reaction zone” scale proportional to the inverse of the mass diffusion activation energy is associated with a small length over which significant mass diffusion is possible. Unlike classic flame theory a still smaller scale is identified with the length over which mass diffusion takes place (i.e., the size of a typical domain of alloyable constituent). Flame speeds are derived for three different geometric configurations of a binary system using a singular perturbation analysis. First a system where the constituents are arrayed in alternating lamina stacked perpendicular to the flame propagation direction is considered. Next, the same system is undertaken except the laminae are stacked parallel to the flame direction. Finally, the elements of these previous problems are combined to investigate the more realistic system of a random media. It is found that the physics for all three of these cases is essentially the same and their resulting flame speeds differ only by a numerical factor (if the correlation length statistic for the random media is considered to be the same as a quarter of the lamina thickness). Thus the more simplified nonrandom models are given more credence at predicting the behavior of systems in practicality.

ISSN:0010-2202    

DOI:10.1080/00102209008951630

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The concentrations of stable species in an atmospheric-pressure, laminar diffusion flame burning a fuel mixture of methane and toluene (1 mole percent) were measured using a microprobe gas sampling/mass spectrometer system. These measurements are compared to results from a flame burning pure methane under identical temperature and flow conditions. In each of the flames studied little or no change is observed in the peak concentrations of a number of major chemical species such as water, carbon monoxide, and carbon dioxide. Small increases occurred in the peak concentrations of hydrogen, acetylene, methylacetylene, vinylacetylene, diacetylene, and butadiene. The presence of increased amounts of these products suggests limited decomposition of the benzyl or phenyl radicals which are likely initial intermediates of aromatic pyrolysis. Relatively larger increases occurred in the peak concentrations of a number or aromatic compounds including phenylacetylene, styrene, and naphthalene. For the toluene flame, the largest absolute differences in peak concentrations were observed for benzene and ethylbenzene. However, a steady state analysis for the concentration of benzyl radical leads to the conclusion that ethylbenzene is most likely formed from the reaction of benzyl and methyl radicals in a highly reversible process. Thus, the dominant toluene destruction pathway appears to be via benzene production. Additional experiments were performed in which the toluene was replaced with benzene, styrene, ethylbenzene or deuterated toluene.

ISSN:0010-2202    

DOI:10.1080/00102209008951631

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Bluff-body and swirl-stabilized flames are similar in that they represent, in simplest terms, the fundamental interaction between a fuel jet and a surrounding toroidal vortex. The vortex in this case is the recirculation vortex which affects the properties of the flames. It is found, not surprisingly, that the two most important fundamental parameters that govern both types of flames are (1) the vortex circulation (Γ), and (2) the fuel jet momentum. Comparisons are made of the properties of the two types of flames using the proper nondimensional parameters, including the fuel-to-air momentum flux ratio and the properly nondimensionalized vortex strength. Such comparisons can help to illustrate the tradeoffs between the degree of swirl and the choice of bluff-body size in devices such as industrial burners, gas turbines, and ramjets. The data also show how one can control flame properties by controlling the vortex strength Γ and fuel momentum and thus gain a degree of control that is not provided by simple jet flames.

ISSN:0010-2202    

DOI:10.1080/00102209008951632

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The pyrolysis oft-butyl alcohol was studied in shock waves in the temperature range 1220-1620 K. The rate constants for the molecular and free radical formation channels were obtained with the help of kinetic modeling of H2O and CO concentration profiles. The rate constants for the runs above 1500 K were corrected for the pressure fall-off effect using the RRKM theory. The Arrhenius expressions for the molecular and radical decomposition channels

ISSN:0010-2202    

DOI:10.1080/00102209008951633

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Methods designed to quench a detonation wave in a pipe usually rely on some passive device which often presents an unacceptable impedance to the normal pipe flow. One method which overcomes this problem is a triggered water spray barrier, the principles of which are examined in the present study.

ISSN:0010-2202    

DOI:10.1080/00102209008951634

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Direct calibration procedures for both the liquid and vapor phases have been developed for use with exciplex-based vapor/liquid visualization systems, in particular for the system composed of 1 % (w/w) N,N,N′N′-tetramethyl-p-phenylenediamine (TMPD)/10% (w/w) naphthalene/89% (w/w) n-decane. For the vapor phase, a sealed temperature controlled cuvet provides a series ofin situreference samples. For the liquid phase, imaged droplets from the edge of a non-evaporating spray are used to provide a range ofin situreference samples. The calibration factors, determined as the measured fluorescence intensity/amount of vapor (or liquid)/unit laser intensity, can then be used to provide absolute calibration for the fluorescent images that are collected from an evaporating fuel spray. Calibrated images, which show the average and transient behavior of evaporating fuel sprays, are presented for the vapor and liquid phases.

ISSN:0010-2202    

DOI:10.1080/00102209008951635

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Using the laser-induced fluorescence method, we have measured relative OH concentration profiles in flat laminar, lean premixed C2H6/O2/N2, flames at 3.2, 6.3, 9.5, and 12.6 atm. By employing a range of flow rates of the combustible mixture, we demonstrate that the reaction zone can be probed at these pressures. In comparison to atmospheric flames, the reaction zone was small and accordingly the [OH] gradient was large; we also observed large gradients in the OH recombination zone. A result of the large gradients is an increase in the noise of the fluorescence signal compared to that at atmospheric pressure. Another impediment to making measurements was beam steering resulting from flame instability, which increased with pressure. We therefore limited our measurements to 12.6 atm.

ISSN:0010-2202    

DOI:10.1080/00102209008951636

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor