摘要:

Abstract–The OH radicals in a hydrogen diffusion flame burning in ambient air were visualized using planar laser-induced fluorescence. Local thicknesses of the OH regions were measured at three downstream distances. Measurements show that the thickness is distributed approximately according to a lognormal probability density function.

ISSN:0010-2202    

DOI:10.1080/00102209308924098

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102209308924097

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A theoretical study is carried out of the combustion of nonspherical carbonaceous particles in the regime of shrinking core reaction. The first problem addressed is the calculation of the pseudosteady temperature and oxidation rate for a particle of given shape. This problem involves the solution of the external diffusion and heat conduction equations with the reaction entering as a boundary condition over the particle surface. Using the boundary integral method, the problem is reformulated as a system of two coupled integral equations which are solved numerically by suitable discretization. The complete transient problem addressing the evolution of particle shape and particle temperature during burnout is similarly formulated by the boundary integral method and solved numerically. Over a broad range of parameters, the pseudosteady particle temperature and rate of oxidation are very nearly equal to those of spherical particles of equal volume and surface area respectively. The transient solutions obtained for parameters typical of pulverized combustion show that during burnout the particle becomes increasingly nonspherical. As expected, nonspherical particles burn faster than spherical particles of the same initial volume, but the difference in burnout times is less than 20% for initial aspect ratios between one and three.

ISSN:0010-2202    

DOI:10.1080/00102209308924099

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

–A numerical model is developed to predict the propagation speed of a Self-Propagating High-Temperature Synthesis (SHS) reaction wave along a vertical cylindrical reactant compact made from a mixture of titanium and carbon powders. A two-dimensional formulation along with convective + radiative heat loss from the peripheral surface to the surrounding inert gas atmosphere is used. The reaction kinetics employed are from the earlier work of Kanury. The model predicts the dependency of the wave propagation speed on various physical and geometric parameters of a titanium + carbon compact. It also predicts conditions at which the reaction wave does not propagate in a self-supporting manner. Effects of peripheral heat losses are also investigated. Some of the predictions are compared with experimentally measured propagation speeds to find excellent agreement.

ISSN:0010-2202    

DOI:10.1080/00102209308924100

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Evaluation of combustion parameters such as ignition delay and combustion duration to study the performance of the reciprocating engines is very important. So far there is no clear-cut method available for the evaluation of these parameters. In this paper the available methods have been reviewed and a new approach has been suggested for the determination of the ignition delay and combustion duration based on the experimental studyon a four-stroke S. I. engine using alcohol as fuel.

ISSN:0010-2202    

DOI:10.1080/00102209308924101

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A theory of finite-size premixed flamelets (“flameballs”), in which the only processes involved are heat conduction, Arrhenius kinetics and diffusion of a light scarce reactant, is extended to account for the presence of a neighbouring cold impermeable wall. Using activation energy asymptotics we show that:(i) owing to its conductive and diffusive influences, the wall leads to two branches of stationnary, approximately spherical, flame balls when it is sufficiently remote.(ii) a non-linear equation with memory effects governs the flame radial dynamics.(iii) only a Lewis-number-dependent part of the upper branch allows for steady states that are stable against radial disturbances.(iv) along the unstable part of the upper branch, the instability is of oscillatory type.(v) by contrast to what happens when near-field volumetric losses are accounted for, no three-dimensional instability shows up.

ISSN:0010-2202    

DOI:10.1080/00102209308924102

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The influence on carbon combustion of the microporous area and of the residues from devolatilization of macerals of original coals has been studied in chemical kinetics controlled regime.

ISSN:0010-2202    

DOI:10.1080/00102209308924103

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An experimental investigation has been made with the objective of studying the mixing mechanism near the nozzle exit in a tone excited non-premixed jet flame. The fuel jet was pulsed by means of a loudspeaker-driven cavity. The excitation frequencies were chosen for the two cases of the non-resonant and resonant frequency identified as a pipe resonance due to acoustic excitation. The effect of different sinusoidal excitation conditions on mixing pattern near the nozzle exit and flame was visualized using various techniques, including schlieren photograph and laser light scattering photograph from TiO2seed particles.

ISSN:0010-2202    

DOI:10.1080/00102209308924104

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The interaction between the sprinkler water spray and the fire induced convective air flow is studied using the field modelling technique. A system of equations describing conservation of momentum, enthalpy and mass is used to simulate the physical picture. Solution of the problem. is divided into two parts: gas phase and liquid phase. In the gas phase, a two-equation k – ε model is used to account for the turbulent effect with the solid wall boundary described by the traditional wall functions. Numerical finite difference method is employed to solve the system of coupled non-linear partial differential equations. The equations are firstly discretized by the Power Law scheme and then solved using the Pressure Implicit with Splitting of Operators (PISO) algorithm. For the liquid phase, the sprinkler water spray is described by a collection of water droplets with different values of initial velocity components and diameter calculated from the Rossin-Rammler distribution function. The motion of each droplet is described by the Newton's Second Law with air drag and convective heat transfer from the fire induced smoke layer. This set of ordinary differential equations is solved by the fourth order Runge-Kutta method for predicting the droplet trajectories. To simplify the physical picture and bearing in mind that evaporative heat loss measured experimentally is small, coupling of the momentum and heat transfer between the smoke layer and water droplets is described by the Particle-Source-In-Cell method. In this way, two-phase flow analysis is avoided by taking the sprinkler water spray as a system of 'hard-spheres'. Neither combustion nor water suppression effect on the burning object is included. However, a 'microscopic' view on the resultant sprinklered fire air-flow pattern, temperature and droplet properties can be visualized. Macroscopic parameters such as the drag to buoyancy ratio and the amount of convective heat transfer are predicted.

ISSN:0010-2202    

DOI:10.1080/00102209308924105

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

It has long been common practice for firefighters to test wildfire potential by lighting single strands or leaves (sheltered from the wind) and observing the rate of spread. This paper discusses single-element fire spread and its potential as a method for determining fine- fuel moisture content and for estimating the likely rate of spread through a fuel complex. Earlier laboratory studies of spread rate along single pine needles and in beds composed of needles have been extended to the case of thin sheet fuels. These include cardboard and Eucalyptus globulus leaves. The dependence of rate of spread on moisture content, fuel orientation and fuel dimensions agrees with previous findings. In addition, the predicted variation of spread rate with moisture content has been tested using experimental data from fine fuels. From the resulting model, the value of single-element testing as a field tool can be assessed.

ISSN:0010-2202    

DOI:10.1080/00102209308924106

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor