摘要:

This paper reports measurements of velocity and temperature in the topping cycle environment found in the aerodynamic duct of the Coal-Fired Flow Facility (CFFF), Details of the measurement methods are given. Also, the measurements are compared with ideal thermodynamic expansion calculations and a multidimensional gas dynamic model of the velocity and temperature within the duct. Discussions of data analyses and numerical model simulations of the flow field within the CFFF supersonic aerodynamic duct are provided. The measured temperature and flow velocity are lower than expected and more representative of subsonic flow rather than supersonic flow. The possible origin of this result is discussed. These results and other measurements in the aerodynamic duct carried out since 1992 demonstrate that on-line optical plasma measurements can be made in the highly stressed, thermodynamic environment that is typical of that existing in a coal-fired MHD generator.

ISSN:0010-2202    

DOI:10.1080/00102209508951892

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Numerical simulations of flames unstable, due to a parametric acoustic forcing, are performed in this paper. Results concerning the threshold of this instability are compared to quasi-steady theoretical predictions. Important disagreements are found at large frequencies, suggesting that the Markstein lengths relative to curvature and stretch are frequency dependent. Results are discussed in connection to experiments and to new theoretical ideas.

ISSN:0010-2202    

DOI:10.1080/00102209508951893

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A theoretical formulation based on maximum entropy principles is presented to predict the droplet size and velocity distributions of sprays in an isothermal environment. The joint droplet distribution function is derived subject to the constraints of mass flow rate, momentum flux, and two modes of energy fluxes (kinetic and surface). A simpler model, which reduces the number of constraints by three, is derived by choosing an adequate velocity integration range. This maximum entropy principle spray model is tested by comparing the calculated distributions with experimental measurements presented by the authors for a hollow cone, non-swirl spray nozzle and the experimental results obtained by other researchers for hollow cone, swirl spray nozzles. For a specific droplet size, the droplet velocity distribution is Gaussian. The droplet size distribution is much more complicated; three types of distributions may occur-positively skewed mono-modal, uniform size (in the limit approaching a delta function), and bi-modal. This study is concerned mainly with the bi-modal size distribution.

ISSN:0010-2202    

DOI:10.1080/00102209508951894

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The mechanism of structure formation during combustion synthesis of titanium silicides was investigated. It is shown that the propagation of an adiabatic combustion wave in a 5Ti + 3Si mixture follows the reaction coalescence mechanism, resulting in fine grains of Ti5Si3crystallizing in the volume of melt. These grains grow rapidly behind the combustion front. Only the Ti5Si3phase appears at the combustion temperature (2130°C), while other silicides (Ti5Si4, Ti3Si, etc.) may crystallize in the cooling zone. Time-resolved X-ray diffraction (TRXRD) analysis of the combustion process and layer-by-layer XRD analysis of the quenched combustion wave were utilized to study the sequence of phase formation. Interaction below the melting point of Ti is negligible in the self-propagating synthesis mode. A particle-foil technique was used to investigate the details of this lower temperature interaction.

ISSN:0010-2202    

DOI:10.1080/00102209508951895

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This investigation is an attempt to predict theoretically, using existing flame modeling capabilities, rich flammability limits for gas mixtures—parameters that are of immense interest to the chemical industry. The system chosen for study is methanol/carbon monoxide/diluent mixtures, where the diluent is either nitrogen or carbon dioxide at pressures of 1,11, and 21 atm, respectively. The critical oxygen concentration needed to sustain a flame, for several mixtures and pressures, was determined experimentally in a spherical vessel with a central ignition source. Burning velocities of 1-D, planar, freely propagating, premixed flames were calculated to determine the minimum oxygen concentration required for these flames to propagate. This minimum O2concentration was found to be consistently larger than that observed in experiments; however, the effects of pressure and diluent composition agreed well with experimental measurements. In order to understand better all the phenomena involved, a transient ignition model was applied to the spherical vessel experiment, which resulted in better agreement with the data. The various comparisons are discussed in detail.

ISSN:0010-2202    

DOI:10.1080/00102209508951896

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper deals with the theory of high-temperature gas-liquid ideally stirred reactors in which a monodisperse droplets or bubbly mixtures react. A new model of gas-liquid combustion reactors is proposed. This model takes into account the principal peculiarities of gas-liquid reactive systems: multistage character of the process as well as its dependence on physico-chemical and structural properties of the medium. The theoretical description of the phenomenon is based on the thermal theory of combustion and interpenetrating continua model of two-phase media. In this approximation the heat and mass balance equations for actual and space-average temperatures and concentrations are obtained. The dimensional analysis of the system of governing equations is used to minimize the number of non-dimensional parameters describing the process in the gas-liquid ideally stirred combustion reactors. In the limiting case of activated reactions the parametrical equation determining stationary states of gas-liquid stirred reactor is found. This equation is applied for classification of the operating regimes of gas-liquid reactors. The peculiarities of the ideally stirred gas-liquid combustion reactors are considered in relation with the change of their regime parameters as well as with the variation of physico-chemical and structural characteristics of gas-liquid media.

ISSN:0010-2202    

DOI:10.1080/00102209508951897

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A three-dimensional combustion model which couples turbulent flow statistics with chemical reactions and radiative heat transfer is used to evaluate the effect of soot and turbulence-radiation coupling on radiative transfer in an industrial-scale furnace. Radiation and soot formation models are presented which include the nonlinear dependencies between fluid turbulence effects, soot formation and radiative absorption and emission in the participating medium. The discrete-ordinates method is used to solve the radiation intensity field. Soot formation is predicted with a formation-destruction model based on local volatile content and stoichiometry. The impact of soot and turbulence-radiation coupling was evaluated based on incident surface fluxes and centerline temperature and emission. Result trends were as expected, but suggest that the magnitude of soot effects on radiative transfer may be less than originally thought for the type of furnace and operating conditions modeled in this research. Predicted local soot properties were significantly different when calculated with and without turbulence coupling. Emissive powers and incident wall fluxes were notably higher when nonlinear turbulence effects were not properly accounted for.

ISSN:0010-2202    

DOI:10.1080/00102209508951898

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A motored, unfired CFR engine was fed with a rich heptane/air mixture. The jacket temperature was maintained at 100°C with a few experiments at 0°C The exhaust vapours were totally condensed by a novel exhaust recovery system. After completely removing cylinder deposits, no reaction products were found at compression ratios up to 14:1. At a compression ratio of 16:1 the charge autoignited/detonated. Subsequently, reaction products were found at a compression ratio of 6:1 and thereafter in increasing quantities up to 14.6:1, the reproducible threshold of autoignition. This entire sequence of experiments was reproduced four times. Samples of the condensate were concentrated by vacuum distillation and subjected to qualitative and quantitative analyses. A very limited range of peroxides and carbonyls were formed in very low concentrations in all experiments where autoignition did not occur. These were identified and their rates of formation calculated. Some thermodynamic inferences were drawn as to their heats of formation. The maximum compression temperatures were calculated. At compression ratios below 16:1, it was concluded that the preflame reaction was initiated on the surface of the combustion chamber, after it had been subjected to autoignitions/detonations.

ISSN:0010-2202    

DOI:10.1080/00102209508951899

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The formation of polycyclic aromatic hydrocarbon (PAH) molecules in laminar diffusion flames is investigated by time-of-flight mass spectrometry combined with laser two-photon ionization. Gas samples from the flames are analyzed on-line with the help of a new inlet system that permits the recording of high-resolution height profiles. Such curves from 13 different flame species of pure and Ar-, C02- or H2- diluted methane flames were measured. Larger PAH are generally found higher in the flame than smaller ones. This behaviour is described by a simple model for successive growth. Some PAH however deviate from this trend and are formed faster than their precursors. This is inconsistent with successive growth and suggests the occurrence of growth by reactive coagulation.

ISSN:0010-2202    

DOI:10.1080/00102209508951900

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Chemiluminescence from species such as CH*, C2*, OH* and CO2* often are used as a quantitative diagnostic in experimental studies of premixed combustion. This paper reports results from a numerical investigation of CO2* chemiluminescence as a quantitative diagnostic in laminar and turbulent premixed flames. Calculations are carried out using a complex reaction mechanism for methane and propane and a model for CO2* chemiluminescence. Relationships between chemiluminescent intensity and both H-atom concentration and heat release rate are quantified as functions of dilution, equivalence ratio, steady and unsteady strain-rate. These relationships are monotonic, but not unique; they depend on which flame parameter is varied. However, the effect of unsteadiness on the relationship for a strained flame is negligible, and this allows the use of chemiluminescence-based diagnostics for measurement of relative H-atom concentration and relative heat release rates in unsteady laminar and turbulent premixed flames.

ISSN:0010-2202    

DOI:10.1080/00102209508951901

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor