Steven G. Buckley

Laser-Induced Breakdown Spectroscopy Detection and Classification of Biological Aerosols

Laser-induced breakdown spectroscopy (LIBS) is examined as a potential method for detecting airborne biological agents. A spectrally broadband LIBS system was used for laboratory measurements on some common biological agent simulants. These measurements were compared to those of common, naturally occurring biological aerosol components (pollen and fungal spores) to determine the potential of LIBS for discriminating biological agents from natural background aerosols. A principal components analysis illustrates that linear combinations of the detected atomic lines, which are present in different ratios in each of the samples tested, can be used to discriminate biological agent simulants from other biological matter. A more sensitive, narrowband LIBS instrument was used to demonstrate the detection of single simulant (Bg) particles in the size range 1–5 μm. Ca, Mg, and Na, which are present in varying concentrations between 0.3 and 11% (by mass) in the Bg particles, were observed in single particles using LIBS.

Real-time measurement of equivalence ratio using laser-induced breakdown spectroscopy

Abstract This paper demonstrates the use of laser induced breakdown spectroscopy (LIBS) as a diagnostic technique to obtain optical measurements of equivalence ratio in a sparkignited engine. Point measurements were obtained in the exhaust manifold of an automotive engine close to the exhaust port of a cylinder. The experimental apparatus was synchronized with the engine in order to obtain measurements in a fixed position during the cycle. Eighty-shot averaged measurements of equivalence ratio P, obtained in under 10 s, were shown to have ΔP = ±0.05 (95 per cent confidence interval). Single-shot measurements were hindered by noise in the signal, but it is shown that the statistical technique of principal component analysis can significantly improve the precision of the data and allows discrimination between measurements obtained in lean, stoichiometric, and rich conditions. The data presented represent one of the first applications of LIBS to optical measurements of the equivalence ratio in an engine, and considerable improvements are expected with further study.

In Situ Species and Temperature Measurements in a Millimeter-Scale Combustor

An FTIR-based spectroscopic technique is described that exploits silicons transmissivity in the IR to make nonintrusive measurements of species concentration and temperature profiles in microcombustors. Species concentration is determined from the integrated absorbance (Beers law), whereas gas temperature is determined by fitting a narrow-band spectral model (EM2C) to CO2 absorption spectra. The technique is demonstrated in a millimeter-scale combustor burning a lean (Φu2009=u20090.86) CH4–air mixture. The results show that accuracies of ±0.25 e-3 mol/L and ±100°C with spatial resolution ∼1 mm are possible. Heat fluxes to the wall are also estimated and thermal losses are found to be very high (∼90%).

Infrared diagnostic technique for microscale combustors

A diagnostic technique is demonstrated for making in-situ measurements of the streamwise evolution of gas temperature and species concentration in a propane-fired silicon-walled microcombustor. The technique capitalizes on the transmissivity of silicon in the infrared by looking through the silicon walls to collect the absorption spectrum of the reacting gas flowing within. This is accomplished by inserting the micro-combustor in the optical path of a Fourier Transform Infrared Spectrometer. Gas temperature is computed from the absorption spectrum of COZ by fitting a narrow band spectral model, EM2C to the spectrum collected by the FTIR. Concentration of CO2 and CH4 are inferred from overall absorbance. The technique has the advantage of being truly nonintrusive as the combustor does not have to be modified in any way to accommodate either instrumentation or optical access. The spatial resolution demonstrated so far is about 1mm in the flow direction but is expected to become smaller as the technique is improved.

IN SITU INFRARED DIAGNOSTICS IN A SILICON-WALLED MICROSCALE COMBUSTION REACTOR: INITIAL MEASUREMENTS

ABSTRACT In situ infrared absorption measurements are performed through the walls of a silicon microcombustor to recover temperature and qualitative trends in major species concentrations as a function of streamwise distance through a partially premixed flame. This technique is shown to have promise for assessing combustion completeness and flame–structure interactions in microcombustors and for extending the boundaries of infrared spectroscopic techniques.

Multiplexed Sensor for Synthesis Gas Compsition and Temperature

The overall goal of this project has been to develop a highly sensitive, multiplexed TDL-based sensor for CO{sub 2}, CO, H{sub 2}O (and temperature), CH{sub 4}, H{sub 2}S, and NH{sub 3}. Such a sensor was designed with so-called plug-and-play characteristics to accommodate additional sensors, and provided in situ path-integrated measurements indicative of average concentrations at speeds suitable for direct gasifier control. The project developed the sensor and culminated in a real-world test of the underlying technology behind the sensor. During the project, new underlying measurements of spectroscopic constants for all of the gases of interest performed, in custom cells built for the project. The envisioned instrument was built from scratch from component lasers, fiber optics, amplifier blocks, detectors, etc. The sensor was tested for nearly a week in an operational power plant. The products of this research are expected to have a direct impact on gasifier technology and the production of high-quality syngas, with substantial broader application to coal and other energy systems. This report is the final technical report on project DE-FG26-04NT42172. During the project we completed all of the milestones planned in the project, with a modification of milestone (7) required due to lack of funding and personnel.