Using PLIF determined flame structure to analyze supersonic combustion efficiencies

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77112/1/AIAA-1999-445-972.pd

Studies of two-region subcritical uranium heavy water lattices

"February 1969.""MIT-2344-13."Some technical reports have the series numbering of MITNE-84Substantially the same as J.W. Gosnell's Ph. D. thesis in the Dept. of Nuclear Engineering, 1969Includes bibliographical references (leaves [212]-215)Reactor physics parameters were measured in eleven two-region subcritical assemblies moderated by heavy water. The regions of the assemblies consisted of nine different lattices of various fuel rod size, U235 enrichment, and spacing. The following parameters were measured in the assemblies: bare and cadmium-covered gold foil radial traverses; bare gold foil axial traverses; the ratio of epicadmium to subcadmium capture r tes in U238 (P28); and the ratio of fissions in U238 to fissions in U233(628)- From analysis of axial traverses at various radial positions, it was determined that the axial buckling was independent of radial position in the assemblies. A method was developed to apply the age equation to the experimental gold foil traverses. This analysis yielded the quantity [ ... ] for each region of the assemblies. Calculated values of [ ... ] were used to obtain values of the infinite multiplication factor from this parameter.For assemblies of sufficiently large inner regions, the values of km so found agreed within experimental uncertainty with independent determinations. The slowing-down spectra. arising from the age theory analysis were used to extrapolate two-region assembly measurements of P28 to critical assembly values. General agreement was found between these extrapolated values and the results of measurements made in full, single region lattices. The heterogeneous expressions for uncollided flux derived by Pilat were extended to two-region assemblies and used to determine single rod values of 628 from two-region assembly measurements. The theory was also used to predict values of 628 for each of the lattices composing the two-region assemblies. Both the single rod values and the full lattice predictions agreed within experimental error with previously reported results. The determination of material buckling from two-region subcritical assemblies is also discussed.!Because of the nature of the assemblies investigated, satisfactory measurements of the material buckling could not be made.U.S. Atomic Energy Commission contract AT(30-1)-234

Images of dissipation layers to quantify mixing within a turbulent jet

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77254/1/AIAA-13435-811.pd

Flame-vortex interactions - Effects of buoyancy from microgravity imaging studies

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76483/1/AIAA-1997-669-671.pd

Visualization of the structure of premixed turbulent flames

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76854/1/AIAA-1988-146.pd

The study of the turbulent burning velocity by imaging the wrinkled flame surface

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76129/1/AIAA-2002-482-348.pd

Combustion Species Sensor for Scramjet Flight Instrumentation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76361/1/AIAA-2005-3574-730.pd

Relationship Between Intermittent Separation and Vortex Structure in a Three-Dimensional Shock/Boundary-Layer Interaction

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140686/1/1.J053905.pd

Blowout of nonpremixed flames: Maximum coaxial air velocities achievable, with and without swirl

The present study demonstrates how to optimize parameters in order to maximize the amount of coaxial air that can be provided to a nonpremixed jet flame without causing the flame to blow out. Maximizing the coaxial air velocity is important in the effort to reduce the flame length and the oxides of nitrogen emitted from gas turbines and industrial burners, a majority of which use coaxial air. Previous measurements by the latter two authors have shown that a sixfold reduction in the NOx emission index of a jet flame is possible if sufficient coaxial air can be provided without blowing the flame out. The coaxial air shortens the flame and forces the reaction zone to overlap regions of higher gas velocity, which reduces the residence time for NOx formation. The present work concentrates on demonstrating ways to prevent flame blowout when the following two constraints are imposed: (1) the coaxial air velocities must be sufficient to shorten the flame to a specified length (in order to reduce NOx emissions) and (2) the coaxial air flow rate must be sufficient to complete combustion without the need for ambient air, which is a common practical constraint. The zero swirl case is considered first, and the effects of adding swirl are measured and directly compared. The following were systematically varied: fuel velocity, air velocity, fuel tube diameter, air tube diameter, fuel type, and swirl number.Measurements demonstrate that coaxial air alone (with zero swirl) can cause up to a twofold reduction in flame length. However, the flame is stable only if the velocity-to-diameter ratio of the fuel jet does not exceed a critical value. It is found that the addition of swirl improves the maximum-air blowout limits by as much as a factor of 6. The results identify a strain parameter, based on the ratio of air velocity to air tube diameter (UA/dA), which collapses the blowout curves for ten different conditions (burner size, swirl number) approximately to a single curve. A physical mechanism that explains the swirl flame data is presented. Swirl is believed to be beneficial because it reduces the local velocities, and thus the local strain rates, near the forward stagnation point of the recirculation vortex, where the flame is stabilized.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29152/1/0000194.pd

Enhancement of flame blowout limits by the use of swirl

The blowout limits of a number of swirl-stabilized, nonpremixed flames were measured, and the observed trends are successfully explained by applying certain concepts that previously have been applied only to nonswirling flames. It is shown that swirl flame blowout limits can be compared to well-known limits for nonswirling simple diffusion flames by using the proper nondimensional parameter, i.e., the inverse Damkohler number (UF/dF)/(SL2/[alpha]F). The fuel velocity at blowout (UF) was measured while four parameters were systematically varied: the fuel tube diameter (dF), the fuel type and thus reaction rate, which is related to the maximum laminar burning velocity (SL), the coaxial air velocity (UA), and the swirl number. Results show that for zero swirl, the blowout curves agree with curves predicted by previous analysis. However, as swirl is added, the flame becomes five times more stable (based on maximum fuel velocity). To explain the effect of swirl, a simple analysis is presented that is an extension of previous nonswirling flame blowout theory. It shows that the conventional swirl number is not the appropriate governing parameter. Instead, a Damkohler number based on swirl velocity is suggested by the analysis and is found to help collapse the data at the rich blowout limit to a single, general curve. Swirl causes a jet-vortex interaction; the recirculation vortex reduces the fuel jet velocity on centerline, which strongly stabilizes the lifted flame. As one increases the fuel tube diameter or the reaction rate (by adding hydrogen), the swirl flame becomes more stable, in a manner similar to a nonswirling flame. Another advantage of swirl is that it makes overall fuel-lean operation possible; the present flame is unstable without swirl for fuel-lean conditions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28591/1/0000399.pd