摘要:

A spouted bed was used to study the effect of temperature on hydrodynamic performance, as measured by parameters such as pressure, minimum spouting velocity, and spout-annulus residence time distribution. Three bed temperature regimes were investigated: ambient, preheat (∼200°C. using a small hydrogen pilot flame), and combustion (∼800°C, using a premixed toluene flame). A stable operating regime for the system under combustion conditions was characterized on a plot of gas velocity vs. equivalence ratio. Pressure and temperature profiles in the bed were developed. The effect of temperature on the minimum spouted velocity was evaluated in terms of the minimum spouting Reynolds number, Rems, and the Archimedes number. The effect of particle shape on spout-annulus flow disribution appeared to be greater than the effect of temperature.

ISSN:0010-2202    

DOI:10.1080/00102209208947214

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An experimental study of C1and C2hydrocarbon species in the post-flame zones of fuel-rich ethylene-air flames at atmospheric pressure and temperatures from 1700 to 1940 K is reported. Most hydrocarbon oxidation occurs via

ISSN:0010-2202    

DOI:10.1080/00102209208947215

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The structure of self-excited and controlled ducted flames was studied by imaging the CH emission and analyzing the pressure and CH intensity time variation.

ISSN:0010-2202    

DOI:10.1080/00102209208947216

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The composition flammability limits of freely propagating premixed hydrogen-air and methane-air flames are investigated. A modified formulation of the plane premixed laminar flame problem is first derived. The resulting parameterized nonlinear two-point boundary value problem is then solved by phase-space, pseudo arclength, continuation methods that employ Euler predictors, Newton-like iterations and adaptive gridding techniques. The efficiency of the method is illustrated by studying the dependence of the peak temperature and the adiabatic flame speed on the equivalence ratio of hydrogen-air and methane-air mixtures. In particular, we discuss the calculation of lean and rich extinction limits in the absence of heat losses. These composition limits for plane adiabatic flames are shown to be physically irrelevant turning points due to flame thickening in finite length computational domains. These artificial turning points are also shown to be dependent on the length of the computational domain.

ISSN:0010-2202    

DOI:10.1080/00102209208947217

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The behavior of strained premixed flames in the presence of swirl has been examined for mixtures, such as lean butane/air and propane/air, for which the Lewis number is significantly larger than one. Solutions are sought using the asymptotic limits of high activation energy and large Reynolds number without restricting the Lewis number to be near one. In this formulation the flame is not necessarily embedded in the viscous layer at the stagnation plane and extinction may occur with the flame located in the upstream inviscid flow. The structure of the viscous layer however is essential in locating the additional stagnation planes that arise at high rate of rotation and hence the flame standoff distance. A detailed description of the flow field is given and the extinction characteristics are determined showing qualitative agreement with experimental observations.

ISSN:0010-2202    

DOI:10.1080/00102209208947218

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The macroscopically steady combustion behavior of AP (ammonium perchlorate)-HTPB (hydroxyl-terminated polybutadiene) propellants containing boron and magnesium was examined using thermocouples and fiber optics and compared with previous results for similar aluminized propellants. Addition of magnesium at constant AP-HTPB ratio was found to increase propellant burning rate moderately while boron increased burning rate substantially. These increases were greater than those previously observed for similar aluminized propellants, A sensitivity analysis was performed to determine the relative importance of various mechanisms such as conductive heat feedback, radiative feedback, and condensed phase heat release. For boron and magnesium the propellant burning rate was found to be most sensitive to changes in condensed phase heat release while the aluminized propellant was found to be most sensitive to radiative feedback. These observations are attributed to the properties of the various metals and their respective oxides. Mg and B have a relatively high propensity to react while on the surface and in the condensed phase of the propellant, thus producing a significant increase in burning rate through condensed phase heat release. Aluminum, being less prone to react in the condensed phase and on the surface, imparts its (relatively weak) influence on the burning rate primarily through enhanced radiative heat feedback.

ISSN:0010-2202    

DOI:10.1080/00102209208947219

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A formalism for a flamelet's evolution of its spatial distribution is derived from a field equation which is slightly more general than Williams' field equation. Unlike Williams' field equation, the field equation used here, though non-linear, has the property that an arbitrary linear combination of interface solutions (Heavyside type of functions) is also a solution. We therefore can describe the location of the flamelet with two interfaces rather than one, both moving relative to the flow in the same direction. The volume between these two interfaces is on average conserved; this makes it possible to define a probability density for the spatial distribution of the flamelet, and thereby derive equations describing the evolution of the spatial distribution of folds and wrinkles of the flame front.

ISSN:0010-2202    

DOI:10.1080/00102209208947220

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Gas turbines offer very high cycle efficiency, exceeding 50% in modern 250 MW-class combined-cycle units for power generation, as well as very low NOvin the lean premixed combustion mode with natural gas fuel. They also account for virtually all commercial aeropropulsion systems, in which case kerosene-based fuel is used. To meet future NOvand CO regulations, a higher level of understanding of turbulence, chemical kinetics and their interactions is required. NOvin particular has become a pacing consideration, although other constraints are present. Selected NOvdata obtained at laboratory and machine conditions with gaseous fuel are reviewed here. Although the important chemical reactions cover a wide range in effective Damkohler number, the measure of turbulence-chemistry interactions, it appears that NOvis formed in a distributed zone manner. Equilibrium and superequilibrium effects can broaden the NOv-forming zones beyond the fine scales of turbulence, even in non-premixed flames. Pressure and the structure of the turbulent flowfield have a diminishing effect on NOvemissions in progressively leaner premixed combustion. Generalizations such as these cannot be made for the related problems of CO emissions and combustion-driven pressure oscillations.

ISSN:0010-2202    

DOI:10.1080/00102209208947221

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The distortion of flames in flows with vortical motion is examined via asymptotic analysis and numerical simulation. The model consists of a constant-density. one-step, irreversible Arrhenius reaction between initially unmixed species occupying adjacent half-planes which are then allowed to mix and react in the presence of a vortex. The evolution in time of the temperature and mass-fraction fields is followed. Emphasis is placed on the ignition time and location as a function of vortex Reynolds number and initial temperature differences of the reacting species. The study brings out the influence of the vortex on the chemical reaction. In all phases, good agreement is observed between asymptotic analysis and the full numerical solution of the model equations.

ISSN:0010-2202    

DOI:10.1080/00102209208947222

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The free boundary problem describing the oscillatory dynamics of premixed gas flame is studied numerically. It is shown (in agreement with recent analytical estimates) that sufficiently far from the stability threshold the flame may suffer backward motion. Simultaneously, the flame oscillations undergo period doubling, similar to that recently observed in gasless combustion.

ISSN:0010-2202    

DOI:10.1080/00102209208947223

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor