Spectroscopic Diagnostic Techniques Research Articles

Combustion diagnostics by laser Raman and fluorescence techniques

With the advent of laser light sources, light scattering spectroscopic diagnostic techniques are assuming an ever-increasing role in a broad spectrum of physical investigations. Of particular importance is the potential application of laser spectroscopy to the hostile, yet sensitive, environments characteristic of those in which combustion occurs. These diagnostic techniques should facilitate greatly improved understanding of a variety of combustion processes which, in turn, should lead to enhanced efficiencies and cleanliness in energy, propulsion and waste disposal systems. Recently, exciting experimental demonstrations of the potential of a variety of Raman processes lspontaneous, near-resonant, coherent, stimulated! and laser fluorescence techniques have appeared in studies dealing primarily with laborator3 flames. Unlike the situation prevailing in the field of the remote detection of atmospheric pollutants, where several comprehensive reviews have appeared comparing the capabilities and systems aspects of various diagnostic approaches, little work of a similar nature has appeared in connection with the remote, localized probing of practical combustion devices, e.g. furnaces, gas turbine combustors. Although the pollutam detection review studies can be drawn upon. the measurement requirements and potential problem areas in practical flame diagnosis are sufficient b different to require a fresh perspective and review of measurement techniques more aptly suited for the extraction of species and temperature information from combustion devices. The object of this paper is to provide such a review. Realisticalt.~. such a review of diagnostic techniques must focus keenly on the problems and sources of noise/interference which must be circumvented for successful application to practical devices. Since it is unlikely thai any one technique will provide species and temperature measurements over the range desired, systems considerations become important in ascertaining hoa the various approaches can be integrated together with maximum measurement rate and minimal redundancy. Such systems studies should

MHD combustor effluent chemistry measurements using Raman scattering

Characterization of the gas chemistry, velocity, pressure, turbulence, and conductivity for coal-fired MHD generators would serve as valuable information for direct correlation with long-term performance of electrode and insulator materials. Gas chemistry is of special significance from a materials performance standpoint since the slag/gas, and hence slag/wall, physical and electrical states are affected by the chemical composition of the channel effluent. In recent years spectroscopic diagnostic techniques have been developed to the point that they can be used to obtain these detailed thermochemical measurements. A specific technique called Raman scattering is discussed and preliminary MHD combustor exit flow data are presented. The primary objective of the study was to determine if the presence of potassium seed would compromise the weak Raman spectral emission from key combustor species.

Laser Raman and Fluorescence Techniques for Practical Combustion Diagnostics

Abstract With the advent of laser light sources. light-scattering spectroscopic diagnostic techniques are assuming an ever-increasing role in a broad spectrum of physical investigations. Of particular importance is the potential application of laser spectroscopy to the hostile. yet sensitive. environments characteristic of those in which combustion occurs. These diagnostic techniques should facilitate greatly improved understanding of a variety of combustion processes which, in turn, should lead to enhanced efficiencies and cleanliness in energy, propulsion, and waste disposal systems.

An investigation of the energy exchange mechanisms involving the 2 3S metastable level in an RF helium plasma

The energy exchange mechanisms present in a pure helium and a helium-neon plasma were investigated using spectroscopic diagnostic techniques. The plasma was spatially resolved and only the volume element at the plasma centerline was considered in the energy- exchange analysis. The experiment was conducted with a constant total pressure of 0·7 torr, a fixed oscillator frequency of 4 MHz, and a constant input power of 1·8 kW. Emission line spectroscopy was used to determine the population densities of 16 levels in the n 3 S, n 3 P, and n 3 D series. Spatially resolved, self-absorption measurements of the 2 3 P-2 3 S transition were used to determine the 2 3 S metastable level number density. The electron number density of 3·3 × 10 13 cm -3 was determined from the spatially resolved H β blue wing profile, and a lower bound excitation temperature of 8800 °K was determined from a Boltzmann plot of the spatially resolved lower bound levels of the excited helium. The addition of 10% and 20% by volume of neon gas caused a measurable decrease in the population densities of the lower bound levels of helium, while the electron number density and lower bound excitation temperature remained unchanged. Three energy exchange models (local thermal equilibrium, corona, and collisional- radiative) were examined, and the collisional-radiative model was found to best describe the excitation processes for the 2 3 S level. This model was also appropriate for describing the helium-neon plasma at this level.