摘要:

The dynamic equation for an aerosol undergoing simultaneous particle formation and coagulation is solved by the moment method, Solutions are obtained that quantify the evolution of the particle volume distribution function (PVDF) for both a size independent and a free molecular collision function. The solutions show that an equilibrium is rapidly established between the source and the coagulation terms and that the particle number concentration N is then proportional to the square root of the source strength. During the interval of equilibrium there is a widening of the PVDF, the moment ratio ƒN = D633/D303, and other width parameters. These quantities may exceed the asymptotic values that apply in the absence of particle formation. The time evolution of the PVDF of soot particles in a laminar diffusion flame is derived using the profile of soot volume fraction that has been observed in recent hi situ optical experiments. This analysis yields the evolution of ƒN, which is necessary to determine the particle number concentration N from the optical data, and the geometric standard deviation σg(t) for the log-normal distribution function. The frequently used assumption that the soot aerosol is mono-disperse (or possesses a constant value of σg) leads to highly distorted profiles of N vs t. We conclude that the optical experiment must be designed to provide a measure of ƒN (or σg) for the soot aerosol in flames if the values of N are to be derived with confidence.

ISSN:0010-2202    

DOI:10.1080/00102208408923805

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Measurements of mean temperature, concentrations of unburned hydrocarbon, carbon monoxide, carbon dioxide and oxygen and of velocity have been obtained in a series of confined kerosene-spray flames. They quantify the influence of mean droplet diameter in the range from 54 to 115 μm, of swirl number in the range from 0.47 to 1.4 and of combustion air temperature in the range from 20 to 225°C. Four flame configurations are identified and correspond to: high swirl, high temperatures and small droplets with consequent droplet evaporation in the recirculation region; larger droplets which penetrate the recirculation region and result in combustion close to the combustor wall; intermediate swirl so that droplets of all sizes penetrate the recirculation region and move upstream and downstream to burn; and weak swirl where the flame is stabilized close to the wall and the main flame extends further downstream. Calculated results are also reported and allow the magnitude of associated uncertainties to be quantified. The inadequacy of the physical information used to support droplet models is emphasized for the larger droplets. With droplet diameters of less than 50 μm, and increasing with preheat temperature, droplet models are unnecessary.

ISSN:0010-2202    

DOI:10.1080/00102208408923806

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Thermal flame propagation into a quiescent combustible mixture consisting of liquid fuel droplets, fuel vapor and air is modelled using the heat release from (i) combustion of single droplets after ignition, and (ii) homogeneous reaction of the fuel vapor in the ambient gas. The purpose of the model is to show how it is possible to calculate a burning velocity acceleration effect due to the presence of liquid droplets in the mixture, in support of a limited number of previous experimental observations. The calculated results for a variety of fuels are in agreement with available experimental data which, however, is mostly outside the range of droplet diameters for which the burning velocity attains a maximum value.

ISSN:0010-2202    

DOI:10.1080/00102208408923807

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

In this study the effects of finite-rate chemistry arc included in a model of flame spread over solid fuels. The gas-phase reaction mechanism is described by the one-step reaction F+ viO→P and the gas-phase fluid-dynamic configuration consists of an opposed flow with a linear velocity gradient. The assumption of local circular symmetry near the flame front reduces the equations for conservation of species and energy in the gas to nonlinear ordinary differential equations. The spreading flame is modeled as a premixed flame arc followed by a diffusion flame. The Damkohler number D and the nondimcnsional activation energy β are the important finite-rate parameters in this model. When D→ ∞ the predictions of the finite-rate model reduce lo the predictions of the previous heat transfer model of Wichman (1983). The theoretical predictions compare favorably with previous experimental results for laboratory-scale flame spread over thermally-thick sheets of polymethylmethacrylate (PMMA) over the entire Damköhler-number range of the data.

ISSN:0010-2202    

DOI:10.1080/00102208408923808

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102208408923809

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A high-speed photographic study has been made of the initiation mechanisms during low-velocity mechanical impact of high explosives in the presence of solid glass beads and hollow glass and polymeric microspheres. In addition, a few experiments were carried out with aluminium and polycarbonate (PC) particles as additives. The explosive chosen was an oxygen-balanced mixture of triaminotrinitrobenzene (TATB) with either ammonium perchlorate (AP) or ammonium nitrate (AN). While the explosive mixture was found to be insensitive to impact, all the additives except aluminium and PC had a sensitizing effect, although by different amounts. The photographic sequences revealed that initiation and propagation events are much more rapid with the glass beads compared to those with microspheres. It is believed that the “hot spots”, leading to faster decomposition rates, are generated via frictional or compressive heating mechanisms depending upon the nature of the inhomogeneity in the TATB/oxidizer/additive mixture. The results have implications for the safe handling of explosives.

ISSN:0010-2202    

DOI:10.1080/00102208408923810

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The main characteristics of diffusion flames formed on a liquid fuel surface with a parallel oxidizer flow have been studied both analytically and experimentally.

ISSN:0010-2202    

DOI:10.1080/00102208408923811

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A pulsating thermal-diffusive instability is predicted at all non-unity Lewis numbers for a simple configuration representing planar diffusional burning of a cloud of fuel droplets moving through gas. The mechanism driving the instability is the coupling of the heat source at the flame sheet to the vapor source at the cloud perimeter. For hydrocarbon fuels, pulsations are predicted for oxygen concentrations well below ambient. This result indicates that thermal-diffusive instabilities can occur in the flame-sheet limit, suggesting new opportunities for investigating the largely unexplored field of the thermal-diffusive dynamics of diffusion flames.

ISSN:0010-2202    

DOI:10.1080/00102208408923812

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Our understanding of laminar-flame behavior was greatly enhanced by Seshadri and Peters' recent demonstration that radicals make a flame resistant to stretch. An error in their analysis, which does not change the basic conclusion but does affect its discussion in detail, is here indicated.

ISSN:0010-2202    

DOI:10.1080/00102208408923813

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Experimental soot threshold results obtained using binary and ternary hydrocarbon mixtures were analyzed to obtain two empirical rules for estimating the onset of soot formation for fuel blends in atmospheric pressure, laminar premixed and diffusion flames. The results suggest that the onset of soot formation for a fuel mixture of known composition can be accurately calculated from soot threshold data for the pure compounds.

ISSN:0010-2202    

DOI:10.1080/00102208408923814

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor