摘要:

Experiments have been conducted to establish temperature stratification conditions under which plume fluid from a fire source will or will not rise to the ceiling, and associated distributions of temperature rise and CO2concentrations. Small fire sources of heptane were used in a pre-stratified, insulated room. A critical, nondimensional, ambient temperature rise from the source level to the ceiling is associated with plume fluid just being able to penetrate to the ceiling, which turns out to be quite insensitive to the shape of the stratification profile, although the values are considerably higher than a value derivable from previous work of Mortonet al. Centerline behavior of temperature rise and CO2concentration agreed well with the theory of these authors up to the theoretical plume reach, but the experimental values needed an incremental height, roughly equal to 25 percent of the theoretical plume reach, to return to zero.

ISSN:0010-2202    

DOI:10.1080/00102209508907779

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Three laser-based techniques have been used for the measurement of relative concentration profiles of the radicals Cl, CH2Cl, and CH3and several major species in a low pressure, premixed, laminar CH4/CH3Cl/O2/Ar flame. The chlorine atom concentration is suppressed throughout the primary flame zone associated with the production of H, O, and OH radicals, but increases rapidly, by the reconversion of HCl to Cl, within an extended flame zone.

ISSN:0010-2202    

DOI:10.1080/00102209508907780

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Particle Image Velocimetry (PIV) is used to measure the instantaneous velocity field in laminar and turbulent premixed flames formed at the exit of a round Bunsen burner. The seeding levels were adjusted to provide data simultaneously in the unburned as well as burned gases. The PIV system employs a double-pulsed laser with a solid state sensor as the recording device. Customized image acquisition is used to quickly process the data, thus rapidly providing the velocity field. Two-dimensional, instantaneous velocity fields are measured in a steady laminar flame and captures the sudden change in flow speed at the flame sides as well as the high speeds sustainable at the flame tip. A wake profile downstream of the flame cone is revealed. Vorticity, strain rates and dilatation are possible with these datasets and are also reported; the strain rate is seen to be a reasonably good approximation to the flame shape with magnitudes measured to be below the extinction stretch rate; the dilatation is seen to provide the closest approximation to the instantaneous flame shape. Turbulent flame tips show similar phenomena occurring instantaneously on convoluted flame shapes. The overall accuracy of the measurements is discussed.

ISSN:0010-2202    

DOI:10.1080/00102209508907781

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The RNG κ-ϵ turbulence model derived by Yakhot and Orszag (1986) based on the Renormalization Group theory has been modified and applied to variable-density engine flows in the present study. The original RNG-based turbulence transport approximations were developed formally for an incompressible flow. In order to account for flow compressibility the RNG ϵ-equation is modified and closed through an isotropic rapid distortion analysis. Computations were made of engine compressing/expanding flows and the results were compared with available experimental observations in a production diesel engine geometry. The modified RNG κ-ϵ model was also applied to diesel spray combustion computations. It is shown that the use of the RNG model is warranted for spray combustion modeling since the ratio of the turbulent to mean-strain time scales is appreciable due to spray-generated mean flow gradients, and the model introduces a term to account for these effects. Large scale flow structures are predicted which are affected by the spray and the squish and are consistent with endoscope combustion images. The effects of flow compressibility on both non-reacting compressing/expanding flows and reacting flows are discussed. It is concluded that predicted combustion parameters, particularly, soot emissions, are significantly influenced by the treatment of flow compressibility in the turbulence model.

ISSN:0010-2202    

DOI:10.1080/00102209508907782

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Experiments have been conducted to seek ways to enhance the selectivity of propene oxide in the autoxidation of propene in the gas phase. The experiments were carried out in two systems, one static and the other a continuously stirred tank reactor, in order to obtain a wide range of conditions. The results reported in this paper have been obtained between 505 and 549K and pressures of 0.9 to 55 bar. Monitoring the perturbation in the product distribution shows that the selectivity of propene oxide is increased markedly on decreasing the temperature. Addition of acetaldehyde to propene: oxygen mixtures, by providing an additional source of peroxy radicals, enhances further the yield of epoxide to the extent that the process could be made commercially viable. Addition of formaldehyde was found not to increase the epoxide selectivity, as its oxidation does not provide an additional source of peroxy radicals. A previously published reaction scheme, constructed to model propene oxidation at low pressures (<4 bar) was tested by simulation of the co-oxidation and high pressure experiments reported here.

ISSN:0010-2202    

DOI:10.1080/00102209508907783

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Engine-out HC emissions were measured in SI engine experiments in which the piston topland crevice size was changed systematically. For a warmed-up engine, the HC emissions were found to be modestly sensitive to the piston crevice size-a 10% change in size results in approximately a 2% change in HC emissions. This low sensitivity is explained in terms of a crevice HC diffusion/oxidation model in the expansion process. When the piston crevice is sufficienlly small, however, the model shows that the HC emissions have a one-to-one correspondence with the crevice size.

ISSN:0010-2202    

DOI:10.1080/00102209508907784

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This study was aimed at comparing the chemical structure of two rich premixed flames Ted respectively with a neat fuel:n-decane and a multi-component fuel, kerosene. Both flames were stabilized on a flat-flame burner at atmospheric pressure. Samples were withdrawn along the symmetry axis with a quartz microprobe and analyzed by gas phase chromatography. The main objective was to justify, for a future modelling purpose, the use of a detailed reaction mechanism validated in then-decane flame to predict the chemical structure of a kerosene flame. A close similitude was observed for the mole fraction profiles of both major species and main intermediates measured in each flame. Relative concentrations of the intermediate species in then-decane flame can be interpreted qualitatively by β-scission of large alkyl radicals.

ISSN:0010-2202    

DOI:10.1080/00102209508907785

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The counterflow diffusion flame subject to time-varying strain rates is studied analytically in order to assess the effect that unsteadiness caused by turbulent flows might have on laminar flamelets. The characteristic unsteady time considered is of the same order as the characteristic flame time, which is represented by the reciprocal of the strain rate, such that the flame structure consists of a quasi-steady reactive-diffusive zone embedded within the outer unsteady-convective-diffusive region. For constant density and unity Lewis numbers, the Shvab-Zeldovich coupling function takes an analytic self-similar solution for arbitrary strain rate as a function of time, thereby facilitating the analysis as well as physical interpretation for the flame-sheet behaviors. We further analyze the inner reaction zone structure using large activation energy asymptotics for one-step overall chemistry in order to determine the extinction conditions. In relation to turbulent combustion regimes, the unsteady effect is expected to modify the flamelet behavior subject to the spectrum of turbulent eddies. That is, although the effective strain rate increases as the eddy scale is decreased, the smaller eddies also have shorter characteristic time such that the flame may not be quenched for some range of eddy scale that otherwise imparts sufficient strain rate to extinguish the flamelet. The results suggest that the applicable range of the laminar flamelet regime may be broader than would be expected from the quasi-steady concept.

ISSN:0010-2202    

DOI:10.1080/00102209508907786

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The burning history of a spherical diffusion flame element (Lagrangian flamelet) is modeled under three distinctive burning conditions: a quasi-steady burning process, a quasi-periodic burning mode, and a purely transient burning condition. In the quasi-periodic burning mode, the time scale of the oscillations is shown to affect the chemistry by providing an observed extinction reignition process associated with the unsteady fuel flux into the flame sheet. For the purely transient burning process radiation extinction occurs for certain soot loadings, initial fuel element sizes, and environmental temperatures.

ISSN:0010-2202    

DOI:10.1080/00102209508907787

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The present work investigates the effect of the addition of water in the form of an emulsion on the combustion of heavy oil. Tests burning neat oil and oil/8% water emulsions are conducted in a large laboratory furnace (0.33 MW thermal input). The effect of the water addition is analyzed by a detailed characterization of the flames as well as of the gaseous and solid emissions.

ISSN:0010-2202    

DOI:10.1080/00102209508907788

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor