摘要:

The steady premixed laminar flame in the stagnation point flow of a flat adiabatic catalytic surface is examined, The fuel-oxidizer mixture is represented as a one-reactant mixture with chemical kinetics controlled by the mass fraction of the deficient reactant. The study is performed for non-unity Lewis numbers. Flame structures and extinction curves are determined with activation energy asymptotics. When the Lewis number (thermal diffusivity over mass diffusivity of the deficient reactant) is below a critical Lewis number (greater than one) extinction occurs with the flame front at the stagnation surface. In this case extinction curves are found to be C-shaped or exceptionally S-shaped and an extension of extinction limits is possible if the catalytic surface reaction is sufficiently strong. Activation energy asymptotic results are compared to exact calculations based on Newton iterations and adaptive grids. The qualitative agreement is good and the general trends are well described by activation energy asymptotics but quantitative errors are found in the predicted extinction limits.

ISSN:0010-2202    

DOI:10.1080/00102208608923881

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

In this paper, measurements of the axial and transverse components of velocity in two-dimensional, sooting laminar diffusion flames are presented. Laser-Doppler anemometry was used to obtain these measurements in flames which, except for the addition of alumina seed particles, were identical to 1- and 2-atmosphere flames for which comprehensive measurements of the soot volume fraction, particle size, and number density, as well as temperature, have been reported previously. The combination of the velocity results with the previous set of measurements allows us to determine the local volumetric rate of soot production, which is observed to increase with pressure.

ISSN:0010-2202    

DOI:10.1080/00102208608923882

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An analysis is carried out of the gas phase ignition of a premixed combustible gas flowing under mixed convective conditions over a hot, non-catalytic or catalytic, cylindrical surface. The surface temperature of the cylinder is assumed to be constant. In the case of the catalytic surface it is also assumed that the catalytic reaction is infinitely fast so that chemical equilibrium is reached along the surface of the cylinder. In the gas, a finite rate chemical reaction with a large activation energy is considered. The analysis makes use of the boundary layer approximation to describe the gas flow and of first order matched asymptotic expansions to define ignition. Explicit expressions are derived for the critical gas phase Damköhler number for ignition as a function of the angular location. The results show that the value of the angular coordinate at which ignition takes place increases as the convective velocity and activation energy increase and as the initial temperature and initial fuci concentration decrease. It is also shown that for the same surface temperature, ignition will occur further downstream from the forward stagnation point if the surface is catalytic than non-catalytic. This is the result of the reduction of fuel concentration near the wall due to the presence of the catalytic reaction. In a practical case, however, where the temperature of the catalytic surface is expected to be larger than that of the non-catalytic one, ignition will occur closer to the forward stagnation point when the surface is catalytic, thus suggesting the use of catalytic surfaces for flame holders.

ISSN:0010-2202    

DOI:10.1080/00102208608923883

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Rates of spread of crown fires predicted by a model are compared to spread rates observed in a series of nine experimental wind-aided crown fires in immature Jack Pine. Selection of two modeling parameters that describe the intensity of radiation issuing from the burning zone within and beneath the live crown layer and from the free flame above the trees is constrained to achieve prediction of the observed spread rate of one fire of the nine documented. Using representative pairs of these parameters, the model predicts the observed rates with rms errors of 0.034-0.037 m/s and maximum absolute error ˜0.06 m/s. Observed spread rates ranged from 0.179 to 0.455 m/s. Prospects for closure of ana prioripredictive model for the spread of crown fires are discussed in the light of these results.

ISSN:0010-2202    

DOI:10.1080/00102208608923884

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The interaction of a methane-air flame with a vortex-ring structure was observed by means of quantitative imaging of the OH concentration using laser-induced fluorescence. The vortex-ring in the experiment was formed by an impulsive jet of gas exiting a thin-plate circular orifice separating a small cylindrical prechamber from the main combustion vessel. This impulsive jet was driven by a spark-ignited flame which propagates through the prechamber. The flame which exits the prechamber orifice follows in the wake of the vortex structure, and eventually overtakes it. A planar sheet of uv laser light from a Nd: YAG-pumped dye laser was used to excite fluorescence in the OH molecules produced by the flame. A two-dimensional image of the OH fluorescence was obtained with a gated image-intensified vidicon camera. The two-dimensional imaging results show the effect on the OH concentration distribution of fluid mechanic features of the vortex-ring structure: a wake flow with a shear layer, a stagnation-point flow, and a vortex core with a high rotational velocity.

ISSN:0010-2202    

DOI:10.1080/00102208608923885

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A simpleA→Bchemical model for plane premixed flames is analyzed with the assumption of both large heat release and large activation energy. The flame structure uncovered under this limit has thick reaction zones and has onlyO(1)changes in flame speed withO(1)changes in flame temperature.

ISSN:0010-2202    

DOI:10.1080/00102208608923886

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102208608923887

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor