摘要:

Scaling properties of the field equation governing propagation of a thin flame front in a turbulent medium are discussed. It is shown that if the turbulent flame velocityuTcan be expressed through the turbulence intensityurmsand the laminar flame velocityu0asuT/u0∞ (urms/u0)x, then α → 1 in the scale invariant regime whenurms→ ∞.

ISSN:0010-2202    

DOI:10.1080/00102208808924005

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The behavior of the fluidized bed combustion of high ash chars is analyzed by applying the two-phase theory, the gas (lowing in plug flow both in the emulsion and bubble phases. The ash is assumed to remain attached to the char particle and therefore the shrinking core model is considered.

ISSN:0010-2202    

DOI:10.1080/00102208808924006

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Propagation of starch-dust air flames has been investigated in a tube (3 m long; square cross section 0.2 m × 0.2 m). Laminar, cellular and slightly turbulent propagation regimes have been observed. Several analogies with premixed gaseous flames have been displayed. Conduction heat transfer through the flame appears to be predominant for preheating the mixture. The burning of the mixture occurs in the gas phase after complete pyrolysis of particles. The laminar burning velocity is found equal to 0.27 m/s, the quenching distance 7 mm, the flame thickness 3-4 mm and the lean flammability limit 70g/m3. Some questions, such as the actual role of flame radiation, are not yet completely elucidated.

ISSN:0010-2202    

DOI:10.1080/00102208808924007

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Radiation codes have been developed based on theS2andS4discrete ordinates approximations which involve solving the radiation transport equation in 4 and 12 directions, respectively. Evaluation of the codes against exact numerical solutions and experimental data show that both these approximations predict radiative fluxes with acceptable accuracy. The models are also evaluated treating them as part of an overall predictive scheme for pulverized coal combustion. The comparative importance of the various input parameters on the model predictions is evaluated via a detailed sensitivity study based on Fourier analysis technique. This analysis shows that the predictions arc most sensitive to the particle number densities and temperatures, while little sensitivity to the absorption and scattering efficiencies is detected.

ISSN:0010-2202    

DOI:10.1080/00102208808924008

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

In this paper, we consider the morphological development and intrinsic reactivity or two microporous carbon chars burning at conditions typical of a pulverized-fuel combustor (i.e., particle temperatures above 1300 K. and diameters below 200 μm). The model chars were chosen for their low ash and volatile matter contents to preclude the complicating effects of these components on the oxidation process. The partially oxidized samples (0 to 65% mass loss), which were collected in an entrained-flow reactor, are experimentally characterized by their total surface area, particle diameter, apparent density. pore volume distribution, and macroporous surface area. SEM photomicrographs of the external particle surface and refiected-light photomicrographs of the internal porosity of the particles are also presented. These measurements demonstrate that combustion occurs under Zone II conditions.

ISSN:0010-2202    

DOI:10.1080/00102208808924009

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The stabilization and diffusional-thermal pulsating instability of burner-stabilized flames, with and without product dissociation, are studied via activation energy asymptotics. The steady solution is characterized by the existence of two flame speeds either for the same heat loss rate or for the same flame standoff distance, while the stability analysis shows that the dual solutions for both cases can be stable, These provide a unified theoretical interpretation of the experimental observations of Spalding and Yumlu for the existence of two flame speeds with the same heat loss rate, and of Ferguson and Keck for the existence of two flame speeds for the same flame standoff distance.

ISSN:0010-2202    

DOI:10.1080/00102208808924010

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

An experimental study of flame and pressure development have been performed in a large scale 50 m3obstructed tube of diameter 2.5 m and length 10 m and with one end closed and one open to the atmosphere. Homogeneous clouds of variable concentrations of cither methane/air or propane/air mixtures have been accelerated in the tube by five regularly spaced obstacles which blocked off 30% of the tube cross-sectional area. Two types of ignition sources were used to initiate the explosions. The planar ignition mode had 19 weak match heads that covered the whole of the tube cross-section at the closed end of the tube. The point source ignition mode used two weak match heads located at the centre-line, also at the closed end of the tube. In addition to the conventional pressure and flame-arrival probes, some of the tests also included hot-wire probes for flow and turbulence measurements.

ISSN:0010-2202    

DOI:10.1080/00102208808924011

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The present work reports measurements of the spectral absorptivities of the eight significant infrared bands for methyl methacrylate vapor. The experimental data were taken at low resolution for temperatures between 400 and 680 K and at a total pressure of 1 atm. Analysis of these data by the statistical narrow-band model yields the spectral-mean parameters for each band, while the wideband parameters have been correlated using both the exponential wide-band model and the Tien-Lowder continuous correlation. These correlated parameters allow convenient determination of the total emissivity, the Planck mean absorption coefficient and super-band parameters.

ISSN:0010-2202    

DOI:10.1080/00102208808924012

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We show asymptotically and numerically that a constant-density flame will exhibit different geometrical shapes which depend on the flow time-scales. In particular, a frozen flow may yield a flame surface composed of bulges connected by cusps, whereas a pulsating flow may dampen the flame motion to the extent that only a flat, laminar flame surface will be possible. The cusp nature disappears when the eddy frequency becomes comparable touLk, whereuLis the laminar flame speed and k is a characteristic wave number of the flow. Flame shapes obtained with a sheet of laser light within a spark-ignited engine show a cusp nature only at low engine RPM, in agreement with the frequency criteria given above.

ISSN:0010-2202    

DOI:10.1080/00102208808924013

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Analytic estimates are developed for depth of penetration and lateral entrainment of negatively buoyant, ceiling jet-driven wall flows during early times of compartment fire scenarios. When walls are not too far from the fire source of the order of the fire-to-ceiling distance, it is found that the penetration of these downward wall flows is a large fraction of the fire-to-ceiling distance, and that this Traction is relatively independent of the details of fire size and fire-to-wall spacing. Also, net rate of entrainment into the wall flow as it is buoyed back upward to the ceiling elevation is found to be several times larger than the Row rate of the driving ceiling jet flow immediately upstream of wall impingement. Data from five studies reported in the literature are reviewed relative to the analytic results obtained. One of these involved a field model simulation of the flow generated by a buoyant source in an enclosure. Two experimental laboratory studies involved fires in enclosures with characteristic dimension of the order of several meters. Two others involved saltwater plumes in freshwater tanks with characteristic dimension of the order of several tenths of a meter. These data are found to be consistent generally with the analytic results, and, in particular, with the notion that the wall Rows in question provide the mechanism for mixing which leads to the deep and rapid stratification typically observed in enclosed compartment fire environments.

ISSN:0010-2202    

DOI:10.1080/00102208808924014

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor