摘要:

The local extinction of bunsen flame tips and edges of hydrocarbon/air premixtures has been experimentally investigated using a variety of burners. Results show that, while for both rich propane/air and butane/air mixtures tip opening occurs at a constant fuel equivalence ratio or 1.44 and is therefore independent of the intensity, uniformity, and configuration of the approach flow, for rich methane/air flames burning is intensified at the tip and therefore opening is not possible. These results substantiate the concept and dominance of the diffusional stratification mechanism in causing extinction, and clarify the theoretical predictions on the possible opening of two-dimensional flame wedges.

ISSN:0010-2202    

DOI:10.1080/00102208208952545

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Experimental results of exit plane NO/NOxemissions from atmospheric monodisperse fuel spray combustion are presented. Six different hydrocarbon fuels were studied: isopropanol, n-propanol, n-octane, iso-octane, n-heptane and methanol. The results indicate an optimum droplet size for minimizing NO/NOxproduction for all of the test fuels. At the optimum droplet diameter, reductions in NO/NOxrelative to the larger and smaller drop sizes typically were in the range of 40-70 percent. For methanol and n-octane, minimum NOxoccurred at droplet diameters of 55 and 48 μm, respectively, as compared to a 50 μm droplet size for isopropanol. The occurrence of the minimum NOxpoint at different droplet diameters for the different fuels appears to be governed by the extent of prevaporization of the fuel in the spray, and is consistent with theoretical calculations based on each fuel's physical properties. Estimates are also given for the behavior of heavy fuels and of polydisperse fuel sprays in shifting the minimum NOxpoint compared lo a monodisperse situation.

ISSN:0010-2202    

DOI:10.1080/00102208208952546

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The steady propagation of a planar flame through a premixed combustible mixture is studied for the case in which the mixture contains two distinct fuels which compete for available oxidizer. It is assumed that sufficient oxidizer is present in the unburned mixture to allow for eventual complete burning of both fuels. Employing the method of matched asymptotic expansions to derive a solution for large activation energies, the propagation velocityUand the effective separation distanceHbetween the points where the two chemical reactions go to completion are determined as functions of standard flame parameters. The analysis extends a recent study by Margolis and Matkowsky (1982a) to include the effects of stoichiometry on flame propagation with multiple fuels.

ISSN:0010-2202    

DOI:10.1080/00102208208952547

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The vaporization of a fuel cloud in an infinite, quiescent atmosphere is examined. A single global parameter which characterizes the vaporization process, and is related to the ratio of the thickness of a vaporization wave to the cloud radius, is identified. Typical fuel sprays correspond to very small (e.g., 104) values of this parameter. An asymptotic analysis of the cloud, predicated on this parameter being small, shows that the cloud and its environment are divided into four distinct regions: (1) the saturated, non-vaporizing cloud interior; (2) a quasi-steady vaporization wave located at the edge of the cloud and propagating radially inward; (3) a quasi-steady (”inner”) region located outside the cloud but in its vicinity and (4) an unsteady (”outer”) region located far from the cloud. A phenomenological model of the vaporization wave is also presented, along with sample calculations using typical cloud data.

ISSN:0010-2202    

DOI:10.1080/00102208208952548

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

In application to turbulent reactive flows, both stochastic models and pdf methods require a model of turbulent mixing. Models currently in use are due to Curl (1963), Dopazo (1979), and Janicka, Kolbe, and Kollmann (1979). For the simple case of decaying fluctuations of a passive scalar in homogeneous turbulence, measurements suggest that the probability density function (pdf) tends to a Gaussian. All the moments of the standardized Gaussian pdf are finite and, in particular, the fourth moment (the flatness factor) is equal to 3. It is shown that the existing models produce pdf's that differ significantly from the Gaussian; in particular, the predicted flatness factors are infinite. An improved class of mixing models is presented that produces pdf's with finite standardized moments. The shape of the pdf produced depends upon the choice of two model parameters. These parameters can be chosen so that the flatness is as small as 3.12 (cf. 3 for a Gaussian), while the recommended model, which has a better overall performance, results in a flatness of 3.70. The shape of this pdf (shown on Figure 5) is close to Gaussian.

ISSN:0010-2202    

DOI:10.1080/00102208208952549

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The ion-molecule chemistry of C3H3+is systematically investigated with a series of alkenes, alkynes, and aromatic molecules under low-pressure, room temperature conditions. Based upon their reactivity differences, two C3H3+structures are distinguished and are assigned as the cyclic (the most stable) and linear isomers. Cyclic C3H3+readily reacts with unsaturated compounds having four or more carbon atoms. Linear C3H3+is found to be even more reactive and, in particular, forms condensation products with acetylene and benzene. The relevance of these results for the higher temperature and atmospheric pressure conditions of a flame environment is discussed. Since C3H3+has been found to be the dominant positive ion for rich and sooting hydrocarbon flames, its high reactivity provides a rapid first step in the ion models of soot formation.

ISSN:0010-2202    

DOI:10.1080/00102208208952550

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

An equation is derived which describes the evolution of a corrugated flame front stabilized in stagnation-point flow

ISSN:0010-2202    

DOI:10.1080/00102208208952551

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The differential diffusion of two species in a turbulent mixing flow is considered. In flows of moderate Reynolds number molecular diffusivities can be a subtantial fraction of the effective turbulent diffusivity and significant differential diffusion can result for species with widely different molecular diffusivities. A theory is presented for the mean and second moments of concentration difference and results are reported for computations for a jet of hydrogen and propane mixing with air. An experiment using Rayleigh scattering to detect the differential diffusion is suggested. Differential diffusion is considered to be very significant in turbulent diffusion flames where molecular and thermal diffusivities are large at high temperatures.

ISSN:0010-2202    

DOI:10.1080/00102208208952552

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

This note draws attention to a result of conduction theory which appears to be little known but is relevant to the development of approximate integral models of flame spread. A semi-infinite plane, emitting a flux of heatq″per unit area whilst travelling at velocityUparallel to the surface of a sink to which the heat source is perpendicular, transfers heat to the sink at a rate (2/π)q″k/Uper unit width wherekis the thermal diffusivity of the medium. This result is compared to the result of a more complex flame spread theory.

ISSN:0010-2202    

DOI:10.1080/00102208208952553

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor