Laser Light Scattering and Fluorescence Diagnostics of Rich Flames Produced by Gaseous and Liquid Fuels

D’Alessio, Antonio

doi:10.1007/978-1-4757-6137-5_8

Cited by 40 publications

(7 citation statements)

References 44 publications

(71 reference statements)

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“…Scattering, calibrated to make an absolute measurement, and extinction can yield the aggregate (or particle) volume equivalent sphere radius R v and volume fraction f v of material and cluster number density n in the sol if the refractive index is imaginary through methods pioneered by D'Alessio (D'Alessio et al 1975;D'Alessio 1981) for soot in ames. Combination of the optical structure factor measurement with scattering/extinction measurements allows for a remarkably complete characterization of aerosols or colloids of particles with a complex index of refraction such as soot (Sorensen et al 1992b;Köylü 1998).…”

Section: Absolute Scattering and Extinctionmentioning

confidence: 99%

“…The classical scattering/extinction method (D'Alessio et al 1975;D'Alessio 1981) relies upon the different functionalities of the scattering and extinction on the aggregate size. It was originally developed under the assumptions of spherical particles in the Rayleigh regime, both of which are limitations for aerosols such as ame soot.…”

Section: Absolute Scattering and Extinctionmentioning

confidence: 99%

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Light Scattering by Fractal Aggregates: A Review

Sorensen

2001

Aerosol Science and Technology

1,014

756

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This paper presents a review of scattering and absorption of light by fractal aggregates. The aggregates are typically diffusion limited cluster aggregates (DLCA) with fractal dimensions of D ' 1:75, which occur frequently in aerosols and colloids, but other types of aggregates are discussed as well. The results of the review are quite general. A scaling description of the scattering of waves forms the basis of our understanding. This description yields the optical structure factor S(q ) of the aggregate, where q is the scattering wavevector, a key quantity. The rigorous approach to the structure factor, the Fourier transform of the density correlation function, is also given and various forms provided in the literature are compared and the best selected. Light scattering is directly related to the structure factor under the assumption of no internal multiple scattering. This so-called Rayleigh -Debye -Gans (RDG) approximation is compared to more rigorous electromagnetic approaches and found to be quite accurate for fractal aggregates. This results despite the presence of internal multiple scattering, which leads to depolarization, and which is also extensively described. For ensembles of aggregates, the effects of aggregate polydispersity on scattering experiments are described and methods for proper analysis are given. A description of optical particle sizing and morphology analysis is given for a complete in situ characterization of the aggregate system. The review relies strongly on straightforward physical reasoning and experimental examples, largely from aerosols, especially those of carbonaceous soot. This paper not only reviews and consolidates, but also presents new results including a scaling analysis of multiple scattering, which leads to depolarization, with a successful comparison to available data and an understanding of structural subtleties; demonstration of the signi cance of a phase shift parameter for evaluating the range of validity of the RDG theory; a Maxwell -Garnet analysis of fractal aggregate scattering; calculations of the albedo and successful comparison to available simulation data; and speculations on multiple scattering and the interior eld. INTRODUCTIONThe purpose of this review is to unify our knowledge of how fractal aggregates scatter (and absorb) light. This is of value for light scattering diagnostics of aerosols and colloids and for understanding the optics of these systems in the environment. The subject has seen able and useful reviews before by Teixeira (1986), Martin and Hurd (1987), Charalampopoulos (1992), and a brief overview by myself (Sorensen 1997). Very recently Fuller and Mackowski (2000) have given an excellent review of the superposition theory of scattering from aggregates. My desire here is to provide an up-to-date and comprehensive review useful for the experimentalist. Any theory that does appear will be based on simple physical arguments rather than detailed mathematical analysis. Many of the general results to be described here apply to nonfractal aggreg...

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Section: Absolute Scattering and Extinctionmentioning

confidence: 99%

Section: Absolute Scattering and Extinctionmentioning

confidence: 99%

Light Scattering by Fractal Aggregates: A Review

Sorensen

2001

Aerosol Science and Technology

1,014

756

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“…The theory which interprets the scattering effects in flames has been exposed in the different review papers (D'Alessio, 1981;D'Alessio et al, 1990) and will be very concisely summarized here. The scattering coefficients of clouds of scatterers can be treated according the Lorenz-Mie theory of spheres and are given by the expression: e.. where N is the number density of the scatterers and f (D) their normalized size distribution, C is the scattering cross section and nand k are the real and the imaginary parts of the refractive index.…”

Section: Optical Apparatus and Measurementsmentioning

confidence: 98%

Optical and Chemical Characterization of Carbon Polymorphs Formed During Spray Combustion of Hydrocarbons

Barbella¹,

Beretta²,

Ciajolo³

et al. 1990

Combustion Science and Technology

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Abslracl-The spray combustion of liquid hydrocarbon fuels produces a large variety of structures containing a great number of carbon atoms (carbon polymorphs) which are or may generate toxic pollutants. These carbon polymorphs include compounds with a main aromatic character and larger aggregates as tar and soot.The spectroscopic properties of these polymorphs collected in a spray flame have been investigated by measurements of their u.v.-visible absorption spectra and fluorescence emission in the visible region. "In situ" spectroscopic characterization has been performed by both laser excited fluorescence and laser light scattering techniques. The comparison of optical data obtained "in situ" in a spray flame with those obtained from the chemical and spectroscopic analysis of the material sampled from the flame has been undertaken in order to attribute the u.v. absorption and the broad band laser excited fluorescence to specific classes of carbon polymorphs.During the heating-up of the fuel droplets there is an enrichment in polycyclic aromatic hydrocarbons and in higher molecular mass aromatic compounds, which eventually contain oxygen. These latter compounds exhibit a more intense fluorescence spectra in the visible region respect to the unsubstituted PAH.

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“…It is well known that individual soot particles formed in laboratory-scale flames are small compared to the wavelength of visible light and spherical in shape (D'Alessio, 1981;Menna and D'Alessio, 1982). As the formation of soot progresses, the elementary soot particles agglomerate to be random clusters which may have a fractal or chain-like morphology due to electrical charging and random collision (Dobbins and Megaridis, 1987).…”

Section: Soot Particles and Agglomeratesmentioning

confidence: 99%

“…On the other hand, scattering characteristics of soot particles can be used to determine the structure of agglomerates and the complex index of refraction of particles (D'Alessio, 1981;Charalampopoulos, 1992).…”

mentioning

confidence: 99%