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A study of the droplet gasification and combustion characteristics of hydrocarbon fuel droplets was conducted at sub- and supercritical. The experimental setup provided quiescent and convective environments under supercritical pressure and temperature conditions. The droplet combustion experiment hardware consisted of: a liquid pressurizing and transfer system; a high pressure and temperature combustion chamber; a droplet formation, deployment and ignition system; and a high speed CCD imaging system. The gasification and combustion characteristics of droplets of several hydrocarbons under quiescent environments were studied. Specifically, the mass emission rates and combustion characteristics of 1.5-mm-diameter suspended droplets of a series of hydrocarbons ranging from hexane (C6) to tetradecane (Cl4) were measured at sub- and supercritical pressures and temperatures using the high-speed image system. The images of droplet gasification and combustion revealed interesting phenomena and provided better understanding of the droplet behavior in sub- and supercritical pressure and temperature environments.

A Laser Doppler Velocimetry (LDV) system and a high speed imaging system were acquired for the Department of Defense (DoD) Grant N00014-97-1-0511 and setup in the Combustion and Emission Control Laboratory at Clark Atlanta University. These instruments have provided an integrated diagnostic system in the areas of combustion, propulsion, emission control, chemical kinetics and fluid dynamics for time resolved flow visualization and detailed quantitative measurements of flow velocities in complex reacting and non-reacting flows. Research projects supported with the acquired instruments included: turbulent premixed combustion, optimization of non-thermal plasma discharge for pollution control, droplet behavior under supercritical conditions, interaction between acoustic waves and fuel droplets and sprays, and combustion instabilities in ramjet combustors. The instruments will also be used on the precombustion pyrolytic degradation of hydrocarbon fuels under normal and microgravity conditions. Seven (7) undergraduate and graduate students from the Department of Engineering and Department of Chemistry at Clark Atlanta University have, so far, been trained and educated on the instruments. The acquired instrumentation has significantly strengthened the University's research infrastructure, and enhanced CAU's capabilities to undertake research that is relevant to the critical technology areas of DoD. These include the chemical kinetics, combustion and propulsion, and fluid dynamics programs of the Army Research Lab (ARL); the aerodynamics, turbulence and internal flows, air-breathing combustion, space power and propulsion, and physical mathematics and applied analysis programs of the Air Force Office of Scientific Research (AFOSR); and the turbulence, propulsion and flow structure interactions, and propulsion programs of the Office of Naval Research (ONR).

A project to conduct experiments to understand the flow and thermodynamic characteristics of liquid fuel droplets and jets in subcritical and supercritical environments was initiated. In the project initiation phase (Phase I), the literature on the subject matter was updated, the experimental setup was designed and modifications in the setup including installation of thermocouples, pressure transducers and analytical and diagnostic devices (LDV, PIV and high speed video imaging systems were either initiated or completed. Preliminary experiments on suspended and free falling hexane droplet gasification and combustion under subcritical and supercritical pressure conditions were undertaken. The preliminary results were very interesting and promising especially with respect to the variation of gasification rate with increasing pressure and decreasing droplet size and the effect of buoyancy on the burning droplet. The project remained slightly ahead of schedule at the end of the reporting period.

Nitrogen oxides (NOx) contribute to the formation of acid rain and ground-level ozone. Cost-effective technologies that destroy NOx from gas stReams are needed. Of particular interest are Non-thermal plasma technologies that offer an innovative approach to the solution of NOx emission control. This study investigates the use of a particular electrical discharge technique, the barrier discharge. Experiments were conducted in double dielectric barrier discharge (DDBD) reactors to elucidate the effects of physical and chemical variables on the NOx removal efficiencies. Analysis instruments included a FT-IR with a length adjustable gas cell, a GC-ms, several gas analyzers and an emission spectrometer. The variables investigated include input power, chemical composition, residence time, and gap spacing. Through this investigation, an overall optimization of DDBD performance was obtained. Of these, we primarily investigated the effect of discharge gap spacing on the electrical and chemical processes that occur in non-thermal plasma discharge (NTPD). A numerical model was developed to simulate the physical and chemical processes during the oxidation and reduction of NOx. Experiments and 1 calculations were performed to investigate the effects of the above-mentioned variables on breakdown electric field, free electron energy distribution, electron impact kinetic rates, and chemical reactions. Results from the calculations and experiments demonstrated the complex relations between NOx removal efficiency and the tested variables. A mechanism of NOx destruction in a NTPD was proposed. This study revealed that the characteristics of microdischarges are the key to understanding the NTPD process. Optical measurements, by means of a high speed intensified imager, provided important information on the microdischarge. This information helped to develop the numerical model, which established the relation between surface charge and charge density within a microdischarge. Results of th