摘要:

The main purpose of this work is to calculate the radiative properties and the radiative fluxes at each location through a fully developed turbulent boundary layer over a solid reacting surface with a diffusion flame. The radiative properties of gas combustion products are obtained using a spectral method especially well adapted for small scale tests. The initial temperature and species profiles needed are given by the resolution of the conservation equations without radiation. The computed emissivities for various gas mixtures including or not soot are in agreement with previous results. The computational method has been used for different systems: polyethylene or polystyrene with O2or air. The results confirm that the contribution of radiation heat transfer to burning rate is negligible compared to convective heat transfer in a laboratory scale test. Radiative heat transfer tends to increase combustion rate only for high soot volume fraction. The values obtained for the various fluxes are in good agreement with the experimental measurements and observations made previously.

ISSN:0010-2202    

DOI:10.1080/00102208008952428

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

In a concentric diffusion flame arrangement, sooting heights were determined as a function of the oxygen concentration in the oxidizing stream. Changing the oxygen concentration has two different and competing effects on the tendency of a fuel jet to soot. Increasing the oxygen concentration increases the stoichiometric flame temperature which in turn increases the fuel pyrolysis and soot formation rates. However, increasing the oxygen concentration also increases the particle burn-up rate in the vicinity of the flame. The initial effect dominates at high oxygen concentrations and the latter at low concentrations. In most practical combustor systems, the temperature would appear to be the controlling parameter.

ISSN:0010-2202    

DOI:10.1080/00102208008952429

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The departure from an equilibrium gas phase behavior is described in order to obtain the rate of mass lossMof a pure carbon particle immersed in an oxidizing atmosphere over a wide range of the Damköhler numberDg(representing either the particle size or the ambient pressure). For equilibrium flow (Dg→∞) complete burning of CO occurs at a flame sheet standing either adjacent to or at a certain distance of the particle. In the former case oxygen is not totally consumed and the burning rate M depends on both, the direct oxidation C + O2and the indirect oxidation C + CO2. In the latter case oxygen does not reach the particle and M depends solely on the indirect oxidation. By loweringDgand treating the flame as a thin but finite zone we establish the dependence ofMon both heterogeneous reactions as well as on the homogeneous reaction CO + O2. The burning rate is reduced whenDgdecreased and the flame moves towards the particle. This behavior persists until the critical Damkohler numberDg°is reached marking the extinction of the CO + O2flame.

ISSN:0010-2202    

DOI:10.1080/00102208008952430

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Kinetic studies on the thermal and oxidative decomposition of untreated cellulosic insulation have been carried out with thermal analytical techniques (TGA and DSC) to provide input parameters for smoldering studies of this material. In dry nitrogen, the weight loss proceeds in one overall step that follows a diffusion-controlled rate law with parameters:A= 1.1 × 1013min-1andE= 39 kcal/mol. In air the decomposition proceeds in two overall steps, the first of which consumes ca 65 percent of the starting material via a diffusion-controlled rate law and has the activation parametersA= 7 × 1014min-1,E= 41.5 kcal/mol. TGA experiments have shown the first oxidative step to be 0.43 order in oxygen mass fraction in the range of Yox= 0.0147 to 0.21. The second oxidation step follows a 3-D diffusion-controlled rate law and has the activation parametersA= 4 × 1010min-1andE= 39 kcal/mol. Heats of thermal and oxidative decomposition have been determined with the differential scanning calorimeter. Heat release rate is not always in direct proportion lo weight loss rate and a differing rate law is more suitable to describe these data.

ISSN:0010-2202    

DOI:10.1080/00102208008952431

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Minimum temperatures for the initiation of smolder in cellulosic insulation materials were measured by the method of Bowes and Townshend (1-D heat flow through a layer on a hot surface). The minimum temperature decreases rather rapidly with layer thickness; a range of about 320°C to 220°C is indicated for layers from 3 to 30 cm thick. Additives (boric acid, elemental sulfur, commercial retardant blend) have a substantially lesser effect; boric acid, the most effective, raises the ignition temperature only about 20°C. Thermal analytical kinetics (DSC) are used, in conjunction with the Bowes and Townshend ignition model, to successfully predict ignition temperatures and to demonstrate that the first overall stage of oxidation of the material is responsible for its ignition characteristics. It is demonstrated that solid reactant consumption, neglected in the model, somewhat distorts the ignition data; oxygen consumption effects are minimal. Boric acid is also the most influential additive on smolder propagation; it doubles the minimum thickness for continued propagation (from 3½ to 6 cm). Additive effects on propagation are determined by their influence on both overall stages of insulation oxidation.

ISSN:0010-2202    

DOI:10.1080/00102208008952432

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

It is shown that the critical shock initiation energy relationship of Walker and Wasley corresponds to the Hugoniot energy delivered during the shock ignition of the material. This relationship thus defines the functional form of the ignition delay time under conditions that the relationship is valid. The concept of a special energy fluence is not relevant. The rudiments of a new shock ignition model are postulated. This model attributes the ignition delay time to be controlled by the time it takes the hot reaction products in small hot spots that are initiated near the shock front to heat and ignite the adjacent solid material, so as to set up a spreading grain burning reaction in the material. The model is qualitatively consistent with the functional form of the critical energy equation under certain conditions, but the ignition behavior is not restricted to that form. Under conditions that the initiating hot spot concentration becomes sufficiently large, the initiation event becomes essentially homogeneous in nature.

ISSN:0010-2202    

DOI:10.1080/00102208008952433

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The fire-ball spectrum of a liquid explosive chosen for its bright and persistent flash has been shown to partially resemble the spectrum of the inner case of a premixed hydrocarbon-air flame.

ISSN:0010-2202    

DOI:10.1080/00102208008952434

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor