Laser Induced Breakdown Spectroscopy (LIBS) is a chemical analytical technique in the early stages of commercialization. The US Army has promoted the development of this technology through the Small Business Innovation Research (SBIR) program. This poster describes recent research activities, specific Army applications, and progress and challenges in the commercialization of LIBS technology.

In this work. we repoil the results of experimental and con1put:itioiial studies on inhibition and extinction of opposed-flow propane (C&)-air tlaines by DMMP (CxH.,OIP). as well as N? and FM-200 (CIF7H) as reference inhibitors. For the dilute flame conditions used in this work (high Z,,), inhibitor effectiveness was si&rnificantly enhanced compared tu previous results with undiluted fuel. However, unlike the previous wwk. OH fluorescence signals. and thus concentrations. did not decrease as the inhibitant concentration wab increased, even near extinction. The cause for this i.emains to be determinrd. Modeling results for a I-D opposrd flow flainc ofthe smie conditions agree with the present results of strady OH levels, while having iilso predicted the decreasing levels fkr the pi-evious work with undiluted fuel.

In this work. we repoil the results of experimental and con1put:itioiial studies on inhibition and extinction of opposed-flow propane (C&)-air tlaines by DMMP (CxH.,OIP). as well as N? and FM-200 (CIF7H) as reference inhibitors. For the dilute flame conditions used in this work (high Z,,), inhibitor effectiveness was si&rnificantly enhanced compared tu previous results with undiluted fuel. However, unlike the previous wwk. OH fluorescence signals. and thus concentrations. did not decrease as the inhibitant concentration wab increased, even near extinction. The cause for this i.emains to be determinrd. Modeling results for a I-D opposrd flow flainc ofthe smie conditions agree with the present results of strady OH levels, while having iilso predicted the decreasing levels fkr the pi-evious work with undiluted fuel.

The application of Laser-Induced Breakdown Spectroscopy (LIBS) is being investigated as a tool for the determination of energetic/explosive materials for a variety of applications.

As part of the continuing effort to find an effective, yet safe, replacement compound for the commonly used halon fire suppression agents, we have begun a study of reduced pressure counterflow diffusion flames inhibited with iron pentacarbonyl (Fe(CO)5). Iron pentacarbonyl has been shown to be a very effective fire suppression agent in small quantities, but there is little understanding of the mechanism of its activity. The goal of this study is to understand the mechanism by which Fe(CO)5 inhibits flames by coupling experimental measurements with computer modeling of diffusion flames. This project is part of the Next Generation Fire Suppression Program (NGFSP).

The goal of this research project is to develop and demonstrate/validate new laser-based instrumentation for the measurement of concentrations of candidate suppressants, oxygen, fuels, and combustion byproducts during suppression of flames and explosions. Time resolved measurement of concentrations of suppressants, oxygen, fuels, and combustion byproducts serve as a check on the repeatability of the tests and help determine why a suppressant is behaving well or poorly in a given full-scale suppression test.

Laser induced breakdown spectroscopy (LIBS) is a variation on the method of spark spectroscopy in which the light from a pulsed laser is focused to produce the spark rather than an electric discharge. This technique (LIBS) has been largely developed at Los Alamos National Laboratory and shown to be useful for elemental analysis, concentration determination, or molecular species differentiation depending upon the experimental configuration. The capability of determining concentration of analytes at high sensitivity gives LIBS an advantage over some other measurement techniques.

Our project on understanding the mechanisms of flame suppression using agents more effective than halon 1301 depends heavily on our ability to study the detailed chemistry of diffusion flames. This paper presents the details of the experimental design of the laser induced fluorescence spectroscopy equipment as well as detection schemes for OH, H, 0 radicals and FeO molecules. INSTRUMENTAL CONSIDERATIONS

As part of the continuing effort to fmd an effective, yet safe, replacement compound for the commonly used halon fIre suppression agents, we have begun a study of reduced pressure counterflow diffusion flames inhibited with iron pentacarbonyl (Fe(CO)s)' Iron pentacarbonyl has been shown to be a very effective fIre suppression agent in small quantities, but there is little understanding to the mechanism of its activity. Unfortunately, Fe(CO)s is highly toxic and thus cannot be used in occupied spaces. The goal of this study is to understand the mechanism by which Fe(CO)s inhibits flames by coupling experimental measurements with computer modeling of diffusion flames. Presented here are results from the spectroscopic examination of uninhibited and inhibited counterflow diffusion flame using emission spectroscopy of active flame species at reduced pressure. The species studied include OH, CH, C2, and iron and iron containing compounds. This project is part of the Next Generation Fire Suppression Technology Program (NGFSTP).

LIBS is a very powerful technique for spectrochemical analysis, particularly for the detection of metals in vapors, aerosols, liquids, and solids. Much of the pioneering work in LIBS development has occurred at Los Alamos National Laboratory1. Typically, a short-pulse laser beam is focussed into the sample causing optical breakdown and the plasma light is collected unto a spectrograph and detected by an array detector. This relatively straightforward set-up affords high sensitivity and efficiency in terms of data generation and collection. In traditional LIBS analyses a single laser is used to vaporize and ionize the sample.

Knowledge of flame velocities is an important factor in the design and construction of many devices involving combustion phenomena. Applications include but are not limited to gun design, fire extinguishment, and internal combustion engines. We report here results of flame velocity measurements obtained using pulsed flame velocimetry. The method developed here is based on and is an extension of the pulsed flame photometer detector developed at Tel Aviv University. Flame velocities for burning methane/oxygen mixtures to which a small amount of inhibitant has been added are determined using pulsed flame velocimetry. Results are compared to flame velocities measured for similar mixtures using other techniques. Relative flame velocities for burning methane/oxygen mixtures doped with small amounts of inhibitants are compared with macroscopic properties such as relative peak temperatures and flame inhibition efficiencies. The utility of flame velocities determined using pulsed flame velocimetry as a predictive technique for inhibitor efficiency studies is discussed.

The internal and translational energy distributions of the OD X 2Π photofragment resulting from the 218 nm photolysis of acetic acid-d are presented. Comparison of these results with those of acetic acid-h photolysis reveals the effects of isotopic substitution on the α-cleavage photodynamics of 1(n, π∗)-excited acetic acid. The OD product contains only approximately 17% more rotational energy than the corresponding OH fragment, and the OD translational energy distributions broaden with increasing fragment rotational level. A pure impulsive model for the dissociation dynamics is inadequate to explain these results. Interpretations which also include contributions from excited state bending motions may be more realistic.

The search for viable replacement fire extinguishing compounds for the presently used Halons 1301 and 1211 has been fully underway for some time. A successful replacement compound has to satisfy a number of criteria, including superior fire extinguishment characteristics. Recent advances in combustion science have opened up the possibility of identifying the detailed physical and chemicAl properties that are responsible for fire inhibition and extinction. 1 We report in this paper some early results of a coordinated experimental and detailed kinetic computer modeling research effort aimed at identifying the fundamental aspects of flame inhibition. The experiments involve the use of infrared Tunable Diode Laser (TDL) absorption spectroscopy to measure temperature, major, and minor, species profiles in a low pressure laminar premixed flame. The detailed kinetic model incorporates a comprehensive fluorine flame chemistry mechanism that was developed recently at NIST. The experiments and modeling involve a number of inhibiting compounds including CF4, CF3H. CF2H2, and C2F6 that were doped up to 1% in CH^/air and CHA/02 stoichiometric flames. This work indicates that each inhibiting compound exhibits a unique behavior in both experimental and computational results with respect to flame structure and adiabatic flame speed characteristics. In addition, the flame models are accurately predicting the chemical pathways of agent decomposition in which the CF3 radicals are implicated in the formation of long-lived toxic intermediate species such as CF20. Overall, our results indicate that the detailed chemical kinetic models have the potential for not only predicting the relative fire extinguishment properties of new Halon replacement compounds, or their mixtures, but also to predict the possible formation of toxic compounds during their use in actual fires.

We are presently conducting experiments in which we obtain both temperature and species concentration profiles of a low pressure, premixed methane/oxygen flame, to which small amounts (0.25 -1.0 %) of a halogenated methane compound have been added. We are using the method of Two Line Thermometry [1], in which a pair of IR active transitions are recorded by tunable diode laser (TDL) absorption spectroscopy and analyzed to determine the temperature of the flame and the partial pressure of the absorbing species. This method offers a nonperturbing probe of flame characteristics and has the abilitiy to operate over a broad range of elevated temperatures. TDL absorption spectroscopy can be used wherever a line-of-sight configuration is possible and background gas absorptions do not interfere.