摘要:

After studying the factors of how the slit width of a slitted bluff-body (SBB) burner influences the cold state flow field, the hot state temperature and gas concentration fields, the following important conclusions are obtained: the slit width influences not only flow characteristics behind the slitted bluff-body such as the size and reflux rate of the recirculation region, but also the quantity of pulverized coal jetting into it. To use it in an industrial plant, the optimal value of slit width is determined as about 10 percents of the width of the bluff-body (BB).

ISSN:0010-2202    

DOI:10.1080/00102209708935638

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Flames tilted by wind are of considerable practical interest because they occur often in our environment and are responsible for a lot of damage. This paper is devoted to the effect of this type of flame on radiative heat transfer which can significantly increase the rate of fire propagation. The proposed theoretical model associates the search for an efficient approach, the facility of use and an acceptable computational time. Its main characteristics are as follows

ISSN:0010-2202    

DOI:10.1080/00102209708935639

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A mathematical model for a three-tiered system consisting of solid, liquid and gas is derived for studying the combustion of RDX propellants. The resulting nonlinear two-point boundary value problem is solved by Newton's method with adaptive gridding techniques. In this study the burning rate is computed as an eigenvalue, which can remove the uncertainty associated with employing evaporation and condensation rate laws in its evaluation. Results are presented for laser-assisted and self-deflagration of RDX monopropellants and are compared with experimental results. The burning rates are computed over a wide range of ambient pressures and compare well with experimental results from one to ninety atmospheres. The burning rate is found to be proportional to the pressure raised to the 0.76 power. Sensitivity of the burning rate to initial propellant temperture is calculated and found to be extremely low, in agreement with past theoretical predictions and experimental data. Results for laser-assisted combustion show a distinct primary and secondary flame separated by a dark zone, the length of which is dependent upon the incident laser flux intensity.

ISSN:0010-2202    

DOI:10.1080/00102209708935640

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A rigorous deduction of a one-dimensional (ID) model of turbulent jet diffusion flames developed for releases of gaseous fuels is presented. This model considers the presence of a non-uniform incident wind and is derived from a full three-dimensional (3D) formulation of the fluid dynamics equations complemented with models for chemical reaction, thermal radiation and an adaptation of the k-ε-g closure method. To deduce the one-dimensional model, the 3D problem is considered to be parabolic along the center line of the flame and self-similar profiles in planes normal to this line are assumed. New terms, not present in previous works, have been introduced in the ID conservation equations and an alternative approach to derive the production terms of the turbulent kinetic energy and of the mixture fraction variance is proposed. To evaluate the validity and usefulness or the model, its results have been compared with those of the three-dimensional model, developed by the authors, and with available wind-tunnel and full-scale experimental results, and a good agreement is found.

ISSN:0010-2202    

DOI:10.1080/00102209708935641

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Distributions of flame front curvature obtained by laser sheet tomography agree with those derived from numerical simulations of passive flame propagation within three-dimensional Navier-Stokes turbulence. The experimental configuration is that of grid turbulence impinging upon a plate which stabilizes a premixed methane/air flame, planar images of the flame allow construction of flame curvature as a function of flame location within the spatial zone that contains products and reactants. In the simulations the flame burning velocity is twice the turbulence intensity and the Reynolds number based on the computed Taylor length scale is approximately 55. The computed flame geometry and flame strain rate are obtained as a function of location based on the mean progress variable (defined by the passive surface displacement or by the scalar fluctuations defined over transverse planes). The shape of the mean progress variable profile compares well with experiment and with two reaction-diffusion models of propagation (KPP and an independent Gaussian model). From the simulations planar slices are created in order to provide curvature information which is directly comparable to the experimental data. Distributions of curvature, based on planar information, exhibit a change with location in the turbulent flame zone: an overall positive curvature (convex to the reactants) at the front to a negative value at the rear; however, this behavior is composed of positive curvature (which by itself has an average value with no spatial variation) and negative curvature (which increases in magnitude with distance from the front). A single length scale allows a good match between experimental and computed curvature throughout the flame zone. The passive flame simulations show the most probable flame shape to be cylindrical, and this feature, allows the planar information to be scaled in order to match the curvature distributions based on three dimensional information. The scaling factor is obtained by observing a cylinder with planar slices at all possible angles.

ISSN:0010-2202    

DOI:10.1080/00102209708935642

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In gas filled porous media the local elevation of pressure slowly diffuses to the adjacent layers of gas inducing the rise in temperature there. In the case of explosive gases this mechanism may lead to the formation of a self-sustaining combustion wave propagating at a constant speed. It is argued that the barodiffusion may be responsible for the occurrence of the so-called high velocity regime often observed in filtration combustion

ISSN:0010-2202    

DOI:10.1080/00102209708935643

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

According to the special feature of the burning process of a single carbon particle under forced convection conditions (Re < 170), a simplified calculation model is presented in this paper. Based on this model, a numerical simulation of the burning process for the carbon particle has been conducted to obtain the burning rates of the carbon particle under different conditions as well as the concentration and temperature distributions within the boundary layer of the carbon particle. Good agreement of the calculated results with corresponding experimental data demonstrates that this model is reasonable for the case with Re⁢ 170.

ISSN:0010-2202    

DOI:10.1080/00102209708935644

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Nitric oxide emission control is one of the major problems encountered in the development of combustion chambers for all types of applications. Scaling rules describing the dependence of NOxemission on operating parameters such as pressure, mixture ratio or turbulence intensity provide useful design guidelines. While such rules are well established for thermal NO, much less is available for prompt NO. This specific problem is considered in this article. The influence of pressure and strain rate on prompt NO production is investigated experimentally in a laminar counterflow diffusion flame. The results relative to the pressure dependence compare well with complex chemistry calculations in well-stirred reactors. The strain rate dependence is in good agreement with previous theoretical results found in the literature. The scaling established for the laminar flame is then applied to a turbulent nonpremixed combustor in order to describe the influence of strain on prompt NO production. The results are analyzed on the basis of a decomposition between global chemical effects and local effects due to strain. The final expression given for the prompt NO scaling in the turbulent diffusion flame provides a good correlation of experimental measurements.

ISSN:0010-2202    

DOI:10.1080/00102209708935645

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A new and computationally profitable theoretical approach based on the first order Born dipole approximation is here applied to evaluate the scattering/extinction properties of randomly oriented filamentary soot agglomerates composed by Rayleigh particles (primary spherules). The influence on the scattering pattern of both the scattering contribution from other spherules in the aggregate and of theself-interactionmechanism is represented. Four main morphologies, i.e., the straight and the zigzag chain, the random and the fractal cluster are considered. Major points evidenced are: (a) the Dissymmetry Ratios (i.e., the ratios of scattered light at two different angles) show very low (< 1%) sensitiveness to the soot refractive index uncertainties as well as to the self-interaction effect, and, vice versa, a pronounced dependence on aggregrate morphology and monomer diameter; (b) the combined measurements of at least two Dissymmetry Ratios are expected to be useful to assess the prevailing aggregate morphology; (c) zigzag chain as compared to straight chain scattering patterns result lo be appreciably different only at scattering angles more than 40"-6O°; (d) the influence of the multiple scattering (i.e., of the scattering contributes from aggregate spherules in the far-field other than the considered primary spherule in the same aggregate) on the extinction factor is not negligible and it is quantifiable below 10% for primary diameters not more 40 nm

ISSN:0010-2202    

DOI:10.1080/00102209708935646

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Temperature and species mole fraction profiles have been measured in laminar premixed H-heptane/02/Ar and iso-octane/02/Ar flames. Both flames have been stabilized on a flat-flame burner at low pressure (6.0 kPa), and species identification and concentration measurement have been performed by mass spectrometric analyses of samples withdrawn locally by molecular beam formation. Temperature profiles were measured by Pt - Pt 10% Rh thermocouples with corrections of the signals to compensate radiative heat losses. A wide range of equivalence ratios extending to 0.7 up to 2.0 has been considered in order to check how the nature of the fuel influences the evolution with this parameter of the species mole fraction profiles

ISSN:0010-2202    

DOI:10.1080/00102209708935647

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor