摘要:

Measurements of mean mole fraction concentration and the rms of the corresponding fluctuations of Freon gas have been measured in an engine configuration where the Freon simulates injected fuel. A Rayleigh-scattering system has been developed to permit the measurements which were obtained with engine conditions defined by a compression ratio of 3.5, a rotational speed of 200 rpm and flat and re-entrant pistons. The results show that the geometry of the fuel nozzle is important 10 the spread of the jet with convergent (spray) nozzles giving rise to improved mixing. The combined effects of swirl, with swirl number of 1.73, and the re-entrant piston is to increase mixing so that values of concentration on the centre line of the fuel jet are reduced by around 50 percent.

ISSN:0010-2202    

DOI:10.1080/00102208808947098

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Using the weak thermal expansion approximation, we derive an equation describing the dynamics of flame propagation in a horizontal channel. The velocity and form of the equilibrium flame front are calculated. A decription is given of the effect of suppression of cellular structure in the flame when the buoyancy effect is sufficiently strong.

ISSN:0010-2202    

DOI:10.1080/00102208808947099

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Data of the optical constants of soot at flame temperature are presented for the visible and infrared regions (0.4-5 μm). Both real and imaginary parts of the refractive index are determined from in-situ extinction coefficient spectra by fitting to theoretical spectra calculated by using the Mie theory in conjunction with a dispersion model. Particle size used in Mie calculation is experimentally determined by using the Diffusion Broadening Spectroscopy technique. Results are presented for different premixed flat flames (methane, propane and ethylene). It is shown that for high H/C ratio in soot, ie.,≥ 0.2, the imaginary part of the refractive index is much less than what is generally considered. Consequently, soot volume fraction determined by light scattering techniques is underestimated in some situations.

ISSN:0010-2202    

DOI:10.1080/00102208808947100

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Flame propagation in swirling flow in a constant–volume chamber with premixed fuel and air has been studied with flame photography and pressure measurement. The entrainment velocity has been calculated by two methods. The first utilizes photographic records to determine flame front propagation rate. From this rate is subtracted the local velocity of the unburned gas (inferred from pressure measurements). The second method utilizes an estimate of the mass entrainment rate inferred from the observed rate of reduction of unburned gas volume, and from pressure measurements. The unsteady velocity signal obtained with a hot wire anemometer has been used with a peak–to–peak counting technique to estimate the micro time and microlength scales of the turbulence and the Taylor rnicrolength scale in the decaying swirling flow in the absence of combustion. Comparison is made with microlength scale calculated using a turbulent entrainment model based on Tennekes turbulence model.

ISSN:0010-2202    

DOI:10.1080/00102208808947101

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

In this paper an efficient method for calculating the sensitivity coefficients of a system of nonlinear two-point boundary value problems is applied to a set of freely propagating, atmospheric pressure, premixed, hydrogen-air flames. The procedure utilizes the Jacobian matrix in Newton's method to generate efficiently first-order sensitivity coefficients. In our analysis we illustrate the effect of variations in the reaction rates and the transport coefficients on the adiabatic flame speed, the temperature and the species profiles. We discuss how the existence of scaling and self-similarity relations among the sensitivity coefficients can imply that relatively simple behavior can exist in complex flames. We also make specific predictions regarding the response of the flame thickness to parametric and species flux disturbances. The sensitivity analysis presented in the paper can also be applied to other more complicated systems. In this way the important kinetic and transport processes in such flames can be determined accurately and efficiently.

ISSN:0010-2202    

DOI:10.1080/00102208808947102

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Discrete ordinates solutions of the radiative transfer equation in two-and three-dimensional rectangular enclosures containing absorbing-emitting-scattering media have been obtained using S2, Se, Sg and Sg, approximations. Evaluation against exact analytical and numerical solutions show that while all of these approximations provide acceptable predictions of the radiation fluxes in twodimensional enclosures, use of the higher order (higher than S1,) approximations is not justified due to substantial increase in computational time and negligible improvement in the accuracy of the predictions. However, for three-dimensional enclosures, the 52 approximation is grossly in error. S1 S1) and S5, approximations predict wall heat fluxes and the temperatures of the medium accurately in these enclosures, but, once again, S4, approximation is shown to be adequate. A study of the sensitivity of the predicted net heat absorption by the walls to the dimensions of the system, and radiative properties of the medium and the surrounding walls, based on Fourier analysis technique, indicates that the predictions are more sensitive to the radiative properties than to the dimensions of the enclosure.

ISSN:0010-2202    

DOI:10.1080/00102208808947103

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

An experimental evaluation of the BLM model of the scalar field in premixed turbulent flames is presented. Experimental measurements of probability density functions (pdfs) of the flame passage times, autocorrelations and spectra were made in open V-shaped and stagnation point flames by monitoring the Mie scattering of the laser beam by a dense oil aerosol which evaporates on passage through a flame front. These results are compared with predictions derived from the model using two a priori pdfs: the exponential and gamma two distributions. The product pdfs are self-similar and well described by the gamma two distribution. The reactant pdfs are also self-similar but are better represented by the exponential distribution except at small passage times. Comparisons between experimental and theoretical autocorrelations show the gamma two predictions to be more successful. The modeling of the low fequency region of the scalar spectra is also improved. Calculations of the integral time scale based on measured crossing frequencies using the gamma two model lead to significantly improved agreement with experimental values. The predicted distribution of the integral time scale, however, is in conflict with the experimental results. The two flame geometries give substantially the same results.

ISSN:0010-2202    

DOI:10.1080/00102208808947104

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This paper considers the negatively buoyant, two-dimensional wall flows that arise during the growth of a compartment fire. Such flows affect the distribution of mass, momentum and energy in the enclosure. The enclosed environment is generally assumed to be comprised of two stably stratified zones in the mathematical modeling of enclosure fires and the transport between these zones is affected by these wall flows. An experimental study is carried out to determine the important thermal characteristics of such negatively buoyant wall flows, particularly the entrainment into the flow, the penetration distance and the heat transfer to the walls of the enclosure. Employing analytical experimental results of buoyancy driven wall and plume flows, the resulting effects in compartment fires are determined. It is shown that the wall flows are very important at the early stages of fire growth,particularly during the establishment of the two zones in the enclosure. Also, the additional transport generated by buoyancy induced wall flows, following the establishment of these zones,is found to be important for a satisfactory modeling of the changing environment in the enclosure.

ISSN:0010-2202    

DOI:10.1080/00102208808947105

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A mechanism consisting of 18 chemical reactions is proposed to simulate the combustion of hydrogen-enriched methane/air mixtures. These include 17 elementary reactions and one global reaction to represent the C2 channel. The simplified reaction scheme has been selected from a comprehensive reaction scheme by using time dependent kinetic flow charts. This technique is also presented in this paper. Good agreements with experimental observations of other investigators were achieved for a wide range of initial conditions. These include 80 KPa <P< 2 MPa, 280 K < T< 650 K, 0.4 < φ< 1.5 and hydrogen to fuel mass ratios,between 0 and 25 percent. A possible explanation for the double peak behavior of the burning velocity along an unhurned gas isentrope. as observed by Miltonand Keck,is proposed.

ISSN:0010-2202    

DOI:10.1080/00102208808947106

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The tri-service Energetic Material Hazard Initiation Assessment Team (EMHIAT) has formulated a five-year research and technology plan to address major deficiencies and needs in the understanding of critical or failure diameter, shock to detonation transition,deflagration to detonation transition, delayed detonation, thermal ignition and response, and initiation via friction,impact, and electrostatic discharge. The study utilized detailed interactions with the solid rocket propulsion industry, with the DoE contractor laboratories, and a review of on-going work in the DoD laboratories responsible for rocket and gun propellants, and explosives. In this paper specific needs are itemized for the eight technical areas listed above, and the Long-Range Plan for hazard mitigation is summarized; the needs and plan elements are organized to correspond to the recent DoD Insensitive Munitions policy.

ISSN:0010-2202    

DOI:10.1080/00102208808947107

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor