A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Using a Burning Rate Emulator to Analyze Flame Extinction Time on the International Space Station(2021) Wright, Anna Elizabeth; Sunderland, Peter B; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There is limited understanding of the fire hazards of liquids and solids in microgravity conditions. As interest in space exploration increases, the need to understand these hazards within spacecraft is of paramount importance. As one of NASA’s Advanced Combustion in Microgravity Experiments, the Burning Rate Emulator (BRE) is used to improve the fundamental understanding of material flammability in microgravity, including the conditions that affect extinction behavior. Oscillation onset and extinction times were measured for emulated flames burning gaseous ethylene and methane diluted with varying amounts of nitrogen using porous 25 and 50 mm BRE burners aboard the International Space Station. Tests were performed with varying fuel flow rates, oxygen mole fractions (XO2) ranging from 0.21-0.4, and pressures ranging from 0.57-1 bar. Relationships between the extinction times and the various experimental parameters were explored to determine what conditions produce longer lasting flames. The measurements are reasonably well correlated by scaling the oscillation onset and extinction times with XO23 Re–0.5, where Re is the jet Reynolds number. These times decrease with increasing burner diameter but are independent of pressure. This is further support of the significant hazards of using enriched oxygen atmospheres in spacecraft.Item Clinorotation time-lapse microscopy for live-cell assays in simulated microgravity(2013) Yew, Alvin G.; Hsieh, Adam; Atencia, Javier; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)To address the health risks associated with long-term manned space exploration, we require an understanding of the cellular processes that drive physiological alterations. Since experiments in spaceflight are expensive, clinorotation is commonly used to simulate the effects of microgravity in ground experiments. However, conventional clinostats prohibit live-cell imaging needed to characterize the time-evolution of cell behavior and they also have limited control of chemical microenvironments in cell cultures. In this dissertation, I present my work in developing Clinorotation Time-lapse Microscopy (CTM), a microscope stage-amenable, lab-on-chip technique that can accommodate a wide range of simulated microgravity investigations. I demonstrate CTM with stem cells and show significant, time-dependent alterations to morphology. Additionally, I derive momentum and mass transport equations for microcavities that can be incorporated into various lab-on-chip designs. Altogether, this work represents a significant step forward in space biology research.Item SMOKE POINTS OF MICROGRAVITY AND NORMAL GRAVITY COFLOW DIFFUSION FLAMES(2009) Dotson, Keenan Thomas; Sunderland, Peter B; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Smoke points were measured in microgravity aboard the International Space Station (ISS) as part of the Smoke Points in Coflow Experiment (SPICE), and in normal gravity conditions. In microgravity conditions increasing the coflow velocity or decreasing the burner diameter increased the smoke point flame length. A simplified prediction of centerline jet velocity did not yield residence-time-based criticalities or data collapse. Simulation of non-reacting flows showed that the simplified centerline velocity prediction was able to predict velocity decay for only relatively weak coflows. An improved model may yield different results. In normal earth gravity coflow velocity exhibited mixed effects. For burner diameters of 0.41, 0.76, and 1.6 mm, smoke points increased with increases of coflow velocity. For an unconfined coflow burner with a burner diameter of 13.7 mm smoke point length decreased with increasing coflow velocity for ethylene and propylene, while increasing for propane flames.Item EFFECTS OF PREHEATED COMBUSTION AIR ON LAMINAR COFLOW DIFFUSION FLAMES UNDER NORMAL AND MICROGRAVITY CONDITIONS(2005-08-30) Ghaderi Yeganeh, Mohammad; Gupta, Ashwani K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Global energy consumption has been increasing around the world, owing to the rapid growth of industrialization and improvements in the standard of living. As a result, more carbon dioxide and nitrogen oxide are being released into the environment. Therefore, techniques for achieving combustion at reduced carbon dioxide and nitric oxide emission levels have drawn increased attention. Combustion with a highly preheated air and low-oxygen concentration has been shown to provide significant energy savings, reduce pollution and equipment size, and uniform thermal characteristics within the combustion chamber. However, the fundamental understanding of this technique is limited. The motivation of the present study is to identify the effects of preheated combustion air on laminar coflow diffusion flames. Combustion characteristics of laminar coflow diffusion flames are evaluated for the effects of preheated combustion air temperature under normal and low-gravity conditions. Experimental measurements are conducted using direct flame photography, particle image velocimetry (PIV) and optical emission spectroscopy diagnostics. Laminar coflow diffusion flames are examined under four experimental conditions: normal-temperature/normal-gravity (case I), preheated-temperature/normal gravity (case II), normal-temperature/low-gravity (case III), and preheated-temperature/low-gravity (case IV). Comparisons between these four cases yield significant insights. In our studies, increasing the combustion air temperature by 400 K (from 300 K to 700 K), causes a 37.1% reduction in the flame length and about a 25% increase in peak flame temperature. The results also show that a 400 K increase in the preheated air temperature increases CH concentration of the flame by about 83.3% (CH is a marker for the rate of chemical reaction), and also increases the C2 concentration by about 60% (C2 is a marker for the soot precursor). It can therefore be concluded that preheating the combustion air increases the energy release intensity, flame temperature, C2 concentration, and, presumably, NOx production. Our work is the first to consider preheated temperature/low-gravity combustion. The results of our experiments reveal new insights. Where as increasing the temperature of the combustion air reduces the laminar flame width under normal-gravity, we find that, in a low-gravity environment, increasing the combustion air temperature causes a significant increase in the flame width.