摘要:

Experimental concentration measurements of the major stable species and five radical species (OH., H atom, O atom, CH., and CH3) obtained on a rectangular Wolfhard-Parker slot burner are compared with a detailed computation of the chemical structure of an axisymmctric laminar, CH4/air diffusion flame burning at atmospheric pressure. In order to examine these CH4/air flames with different geometries and different sizes, the species profiles are plotted as functions of the local mixture fraction, and the scalar dissipation rate has been matched in a region around the stoichiometric surface. The overall agreement in the absolute concentrations, the shape of the profiles, and their location in terms of the local mixture fraction is good to excellent for the stable species (except for O2) and for the most abundant radicals OH, H atom, and O atom. For example, the calculated OH- maximum concentration is in much better agreement with the experimental results than are full equilibrium and partial equilibrium estimates. Less satisfactory agreement is found for the CH. and CH3radicals. In addition, significant discrepancies are observed in the temperature field and in the degree of O2penetration into rich flame regions.

ISSN:0010-2202    

DOI:10.1080/00102209308907601

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A transport equation for the flame surface density is used to describe premixed turbulent combustion in the simple case of a one-dimensional propagation in a homogeneous mixture. An analytical method of the type devised by Kolmogorov, Petrovski and Piskunov, as well as numerical simulations, are exploited to study the influence of turbulence and laminar flame speed on the turbulent flame speed and on the turbulent flame thickness. It is shown that the model exhibits steadily propagating turbulent flames and that flame speed is proportional to the square root of the turbulent viscosity multiplied by the effective strain rate of the flow. If these two quantities are evaluated with classical expressions one finds that the turbulent flame speed is proportional to the square root of the turbulent kinetic energy (St= λAu′). This result agrees well with other experimental and theoretical expressions and correlations available in the literature. The comparison with experiments yields one of the constants of the model. The nonsteady formation of the turbulent flame brush is then examined to complete the description of the turbulent combustion wave dynamics. Two characteristic times of the turbulent ignition processes are revealed and the flame initiation is described analytically and numerically. The calculations indicate that the transport equation used to model the balance of flame surface provides a suitable description of turbulent flame propagation in one dimension. In addition, the results may be used to adjust the constants appearing in the balance equation for the flame surface density.

ISSN:0010-2202    

DOI:10.1080/00102209308907602

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In order to elucidate the interrelationship between flame structure and noise characteristics and to obtain those properties which are easily measurable and understandable, and are strongly correlated with the acoustic pressure perturbation, three kinds of flames with different structure are first formed in a plane shear layer by varying the flow and turbulence conditions: a flame within which organized eddies are clearly observed, a flame which has a rather complicated appearance and a higher eddy-formation frequency than the first due to the increased mean convection velocity, and a flame without any organized eddy, which is stabilized under the same flow conditions as the first flame, but has increased turbulence levels. Simultaneous measurements and FFT-analyses of the fluctuations of sound pressure, ion current, temperature, and CH-emission are made on these three flames. The results are shown concerning not only clear properties of the correlations between flame structure and sound intensity, but also the directionality and spectral characteristics of the combustion noise.

ISSN:0010-2202    

DOI:10.1080/00102209308907603

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Experimental results concerning combustion of freely falling particles of copper, tungsten, steel, tantalum and molybdenum are presented in this paper. The experiments were carried out by the setup based on a method of forming and igniting monodisperse metal particles in pulsed discharge, developed at Odessa State University.

ISSN:0010-2202    

DOI:10.1080/00102209308907604

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In situ LIF measurements of PAC concentrations were made in fuel rich natural gas flames, in the semi industrial scale MIT Combustion Research Facility.

ISSN:0010-2202    

DOI:10.1080/00102209308907605

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The objective of this research is to study near-critical and super-critical combustion of droplets consisting of binary fuel mixtures. Experimental results are reported on the burning of fiber-supported droplets of mixtures of n-heptane and n-hexadecane, initially about 1 mm in diameter, under free-fall microgravity conditions. The ambient pressures range up to 3.0 MPa, extending above the critical pressure of both fuels, in room-temperature nitrogen-oxygen atmospheres having oxygen mole fractions of 0.12 and 0.13. Three-stage burning of the binary fuel droplets is observed, and the onset lime of the second stage is compared with the predictions of an existing theory. Experimental evidence of thermo-capillary and/or diffuso-capillary convection during the droplet burning is obtained. The results contribute to improving understanding of binary-fuel droplet-combustion processes at high pressures.

ISSN:0010-2202    

DOI:10.1080/00102209308907606

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The vaporizalion and pyrolysis of a heavy fuel droplet moving through a high temperature inert gas is analyzed, with special emphasis on fuel chemical composition and how it changes during the droplet lifetime. A mathematical model is proposed based on a number of simplifying assumptions, including distillation-like vaporization. With this model the relation between droplet size, asphaltene fraction and coke residue formation has been examined. Calculation results show that finer atomization is a good way to reduce coke formation. These results further indicate that experiments with large droplets or with thermogravimetric apparatus may lead to wrong conclusions as to the coke residue farming tendency of heavy fuel sprays in atmospheric combustion devices.

ISSN:0010-2202    

DOI:10.1080/00102209308907607

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An experimental and numerical investigation of premixed methane combustion within a nonhomogeneous porous ceramic was performed. The burner consisted of two porous ceramic cylinders of equal length and diameter that were stacked together and insulated around the circumference. Four series of experiments were carried out to determine the lean limit using three different pore sizes in the downstream ceramic cylinder (SBR). The pore size in the upstream ceramic cylinder was constant in all four cases. A new definition of the lean limit was introduced to account for the effects of the porous ceramic. The burners were tested over the range of lean limit 0.41 < φ≤ 0.68 and the numerical simulations were performed over 0.43 < φ ≤ 1.0. The results demonstrated that porous ceramic burners provide a range of stable burning rates at a constant φ, The maximum flame speed inside the burners was much higher than the premixed, freely burning adiabatic laminar flame (free flame) speed. The lean limits in the porous burners were lower than that of the free flame. The effects of SBR pore size on the burner performance were also determined. Flame stability characteristics at the interface and exit plane are revealed both numerically and experimentally. The numerical model in this study predicts the combustion phenomena within the porous ceramics with reasonable accuracy. The model can be used to guide future experimental burner designs and tests.

ISSN:0010-2202    

DOI:10.1080/00102209308907608

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The present paper gives a mathematical model for collapse and ignition of reactive gas-filled bubbles. Oxyhydrogen bubbles, which can be formed in high-temperalure reactor water, can present an explosion hazard. In addition to treating the classical features of bubble dynamics, energy balances for the liquid and gas phase, and the heat transfer between the gas and surrounding liquid are included in the model. The gas-phase thermodynamic properties and chemical reaction rates are assembled by incorporating a real-gas version of the CHEMKJN chemical kinetics package in which the Nobel-Abel equation of state is used. The liquid energy equation is solved by the integral method to yield an ordinary differential equation for interface temperature. Some typical numerical results and shock ignition thresholds, or critical shock pressures necessary to ignite the gas-phase mixture, under various conditions for argon-diluted hydrogen/oxygen bubbles in water and glycerin are presented. Comparison with experimental data indicates that the model can predict the process of bubble collapse and ignition accurately, especially if ignition occurs during the first cycle. Calculations show that initial bubble radius, temperature, pressure, and mixture composition have strong influences on bubble collapse and ignition. The ignition threshold decreases with increasing initial radius and temperature and decreasing initial gas pressure. Ignition is also favored by stoichiometric or fuel-rich mixture diluted by inert gas.

ISSN:0010-2202    

DOI:10.1080/00102209308907609

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A combustor for lean mixtures, employing heat recirculation and a new gas burner generating a swirling central flame, was developed and tested. Stability curves for burning lean mixtures of methane/air were determined. The leanest mixture which was burned before extinction, at a preheat temperature of 540° c and a flow rate of 1000 × 10−6m3/s, contained 3.2% of methane. This figure is 60% of the normal flammability limit. The stability curves were determined at mean preheat temperatures of 35, 460 and 555° c, and for burners with some different geometrical parameters. Special attention has been paid to explore the effect of entrainment of uncontrolled amounts of air on the stability curves.

ISSN:0010-2202    

DOI:10.1080/00102209308907610

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor