A free-piston rapid-compression facility (RCF) has been developed at the University of Michigan (UM) for use in studying high-temperature combustion phenomena, including gasphase combustion synthesis and homogeneous charge compression ignition systems. The facility is designed to rapidly compress a mixture of test gases in a nearly adiabatic process. A range of compression ratios, currently 16 to 37, can be obtained. The high temperatures and pressures generated by the RCF can be maintained for in excess of 50 ms, providing an order of magnitude increase in observation time over what can be obtained using shock tubes. The facility is instrumented for temperature and pressure measurements as well as optical access for use with laser and other optical diagnostics. This work describes the UM-RCF and its operation, establishes obtainable pressures and temperatures (over 1900 kPa and 970 K for predominately N 2 gas mixtures, and over 785 kPa and 2000 K for Ar gas mixtures), and demonstrates the repeatability of the UM-RCF experiments (< 3% run-to-run variability in peak pressure) for combustion studies. The experimental results for time histories of temperature and pressure are interpreted using analytical isentropic models. Comparison between the isentropic predictions and the experimental data indicate excellent agreement and support the conclusion that the core region of the test gases is nominally uniform and is compressed isentropically.2
The current work presents the results of an experimental investigation of gas-phase combustion synthesis of silica (SiO 2 ) particles using a multi-element diffusion flame burner (MEDB, a Hencken burner). Silane (SiH 4 ) was added to hydrogen/oxygen/argon (H 2 /O 2 /Ar) flames to produce SiO 2 nanoparticles at various burner operating conditions ( ϭ 0.47-2.16). To characterize the burner performance, temperature measurements were made using water absorption spectroscopy and uncoated, fine-wire thermocouples. The results demonstrated the non-premixed flow arrangement of the fuel tubes and oxidizer channels of the MEDB provided uniform, ϳ1D conditions above the surface of the burner, with temperature variations of less than Ϯ3% in the transverse direction (parallel to the surface of the burner) for elevations above the mixing region (z ϭ 0 -7 mm), extending to heights Ն 30 mm. At heights above the mixing region, approximately constant axial temperatures are also observed. Silica particle formation and growth were examined for comparison with current understanding of the physical mechanisms important in combustion synthesis of SiO 2 . The particle properties were determined using transmission electron microscope (TEM) imaging. Geometric mean diameters of the primary particles varied from d p ϭ 9 to 18 nm. The current study demonstrates the utility of the MEDB in providing a controlled environment for fundamental studies of gas-phase combustion synthesis phenomena, as well as offering broad flexibility in experimental design with control over process variables such as temperature field, particle residence time, scalable reactant loading, and particle precursor selection.
Results of an experimental study of the application of frequency-modulated UV laser absorption spectroscopy to silica (SiO 2 ) particle-forming flames (SiH 4 /H 2 /O 2 /Ar) are presented. An argon-ion pumped ring-dye laser system in the rapid wavelength scanning configuration was used to obtain multiple line shape profiles of the R 1 (7) and R 1 (11) , respectively). Temperature and OH mole fraction were determined by a best fit of a convolved Voigt absorption profile to the data. Measurements were made in the multiphase regions of silane/hydrogen/oxygen/argon flames, verifying the applicability of the diagnostic approach to combustion synthesis systems. Absorption measurements were taken over a range of particle environments found at increasing heights above the burner surface (5-20 mm) and equivalence ratios ( ס 1.0 and 1.2). The experimental data were compared with thermocouple measurements, equilibrium, and one-dimensional modeling simulations. The results of the study successfully demonstrate OH UV absorption spectroscopy as a highly sensitive and accurate (uncertainties less than %01ע in the current work) diagnostic approach for in situ measurements of temperature and OH mole fractions in combustion synthesis flames.
: The Illinois v. Milwaukee Federal District Court decision is the most far reaching application yet of the federal common law of nuisance to interstate water pollution conflicts. Although a Federal Appelate Court recently rescinded part of the district court decision, Milwaukee must still upgrade its metropolitan sewage system to a level beyond that required by federal and state regulations. The improvements must be completed with or without federal aid. The case points out the apparent inability of the Clean Water Act, the most comprehensive federal legislation affecting the nation's water quality, to deal with certain interstate water quality conflicts. The Milwaukee decision could set a precedent for similar settlements elsewhere which may in turn affect the U.S. Environmental Protection Agency's water quality clean up program. A more integrated, ecosystem conscious approach to management of shared water resources (e.g., the Great Lakes) would help reduce the need for court decisions like Illinois v. Milwaukee.
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