摘要:

Abstrac–-A two-color LDA technique has been developed for conditional sampling of turbulence intensity and Reynolds stress in premixed turbulent flame. To sample conditionally in the unburned reactants, silicone oil aerosol which burned and evaporated by combustion is used to seed the flow. Conventional AI2O3seed particles are used to sample unconditionally through the flame. A conditional analysis method is developed to deduce conditioned data in the burned products from the unconditioned data. Comparison of the conditioned and unconditioned data obtained in a lean ethylene/air v-flame shows that the so-called "flame-generated turbulence" and the increase in Reynolds stress within the flame brush are caused primarily by intermittent measurements in the reactants and in the products. Using an intermittency model for the flame turbulence, the contributions due to intermittency are shown to be proportional to the difference between the conditioned mean velocities. The conditioned fluctuation intensities in the product are generally higher than those in the reactants indicating production of turbulence by the flame. The fluctuations in the products show rapid decay beyond the turbulent flame region.

ISSN:0010-2202    

DOI:10.1080/00102208408923826

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Abstraet–The one-point, one-time description contained in the Bray-Moss-Libby model of premixed turbulent combustion is first generalized to a two-point, two-time formulation which includes information on the time and length scales of the scalar field within turbulent flames. This formulation is then specialized to a one-point, two-time description which is treated in detail so as to yield expressions for the autocorrelation of the progress variable, for the time scale of the scalar field, for the mean crossing frequency of the flamelets and, finally, for the mean rate of chemical reaction. Although the latter expression closely resembles results developed earlier on an intuitive basis, its derivation in the present study permits an assessment of various assumptions and intermediate results by comparison with experimental measurements. Such comparisons as are currently possible are shown to lend support to the analysis and to enhance the prospects of future exploitation of the general formulation.

ISSN:0010-2202    

DOI:10.1080/00102208408923827

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Abstract–The effect of temperature on soot formation in a laminar propane diffusion flame was investigated. The temperature of the flame on a Parker Wolfhard burner was varied by adjusting the inert nitrogen content in the oxidizer Row. Local soot aggregate properties, such as aggregate diameters and their number densities as well as soot volume fractions were determined using simultaneous laser light scattering and extinction methods, while spherule diameters were obtained using sample extraction and transmission electron microscopy. Soot volume fractions and aggregate diameters were seen to increase with height above the burner, while the opposite trend was noted for aggregate number densities for the three flame temperatures investigated. Spherule diameters were seen to increase with height particularly in the early part of the flame. An increase in temperature resulted in a considerable increase in local soot volume fractions and aggregate diameters. Spherule size and degree of agglomeration also varied somewhat with temperature. Soot aggregate number densities, at least in the regions of noticeable soot loading, were found to be largely insensitive to changes in temperature. Heights above the burner were converted to residence times in the flame allowing for buoyancy. The mean rate of growth of the largest soot aggregates was found to be essentially independent of flame temperature, although the absolute soot particle diameters were larger in the hotter flames, resulting in an increase in sooting with temperature. An "effective growth residence time" was introduced to take account of the effects of temperature such that both total soot loadings and maximum soot diameter were the same for any given normalized time for all flame temperatures investigated.

ISSN:0010-2202    

DOI:10.1080/00102208408923828

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Abstract–Much of the previous effort on the stability of plane, freely propagating flames to short-wave perturbations is based on the constant-density approximation (CDA). Such a treatment achieves analytical simplicity at the expense of ignoring thermal expansion. It is valid only when the heat release is small, either due to weak exothermicity or scarcity of reactants, hardly the state of affairs in real flames. This paper treats the stability question without invoking the CDA, and finds that when thermal expansion is taken into account, the Lewis-number stability band disappears. In the limit of long-wave perturbations, the present results agree with those obtained recently by several authors by means of the Slowly-Varying-Flame approach.

ISSN:0010-2202    

DOI:10.1080/00102208408923829

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Abstract–Diffusion (wick) flames were used to study relative soot production from methanol and hydrocarbons in binary liquid solutions. Methanol-toluene and methanol-benzyl alcohol solutions, prepared with C-14 labeled methanol, were burned. Comparison of sott radioactivity with that of the binary solutions indicated that fuel-to-soot conversion is 35-40 times greater for toluene carbon-benzyl alcohol system. Increasing methanol content in the liquid fuel decreased the rate of total soot generation. No soot was collectable at concentrations above a threshold of 0.94 mole fraction methanol. This threshold was also observed in parallel soot generation studies using a visible-light spectrophone and in measurements of flame luminosity as a function of fuel composition.

ISSN:0010-2202    

DOI:10.1080/00102208408923830

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Abstract-The flow field near the attachment point on a high-speed flame holder is approximated as a combination shear and straining flow. This flow field models the flow field near a separation point and analysis of premixed flames in this flow field is performed assuming large activation energy. Blow-Off is predicted as a function of the local straining rate and is independent of the shear. Comparisons are made with experimental data.

ISSN:0010-2202    

DOI:10.1080/00102208408923831

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102208408923832

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor