STS-94 Mission Science Report # 16s
Thursday, July 10, 1997 6 p.m. CDT
The study of fire dominated the Microgravity Science Laboratory -1 investigations in Columbia’s Spacelab, today.
This morning Payload Specialist Dr. Greg Linteris completed a run in the second phase of the Droplet Combustion Experiment. The run is part of a three phase study to map the burning characteristics of heptane fuel droplets over a range of atmospheric pressures. The first phase --conducted earlier in the mission -- burned fuel droplets at one atmospheric pressure, the same as on Earth. The second phase burned the droplets at one-half atmospheric, while the third will burn droplets at one-quarter atmospheric pressure.
“In each phase, we are keeping the pressure the same and slowly reducing the oxygen to see if the fuels can still burn and if so, how they burn,” said project scientist Dr. Vedha Nayagam of NASA’s Lewis Research Center in Cleveland, Ohio. “On Earth, we encounter low combustion scenarios -- for instance, in gas turbines -- so it’s important to know what happens when pressure is reduced.”
“We wanted to expand our data base at one-half atmospheric pressure,” said co-investigator Dr. Fred Dryer of Princeton University in Princeton, New Jersey, “so we combined two of our gas bottles that had been slated for one-quarter atmospheric pressure studies to yield a one-half atmospheric condition in the test chamber.” The one-quarter atmospheric runs are scheduled for later in the mission.
Linteris burned three sizes of heptane droplets -- 4 mm, 3 mm and 2 mm. The 4 mm droplet extinguished after burning 5.9 seconds--leaving behind a relatively large droplet. The smallest droplet burned about nine seconds -- using almost all of the fuel.
“The large droplet extinguished early in its burn time due to loss of significant combustion energy by radiation,” said Dryer. “The small droplet burned to near completion because less energy is lost by radiation as the droplet’s initial diameter is decreased. We would have received opposite results if we’d conducted this same experiment on Earth.”
Basic knowledge gained by the mapping of these various burning regimes will be used by scientists to design better combustion systems, such as combustors and propulsion systems, to extract maximum efficiency while minimizing unwanted pollutants.
After Linteris completed the series of runs to study burning fuel drops, both he and Mission Specialist Dr. Don Thomas took a planned half-day break.
Late this morning, a palladium-silicon sample completed an 11-hour processing period in the TEMPUS levitating furnace facility. The sample went from a solid state to a molten state and then was undercooled 16 times. The co- investigator, Bob Hyers of the Massachusetts Institute of Technology in Cambridge, Massachusetts, said this particular sample was chosen because it is a glass forming metal with many industrial applications.
“Preliminary results look very promising,” said Hyers. “We got a wide range of temperatures and achieved a reasonable amount of undercooling.”
A sample of palladium copper and silicon is now processing in the levitation furnace. Knowledge gained from this study, led by Dr. Ivan Egry of the German Aerospace Research Establishment in Cologne, may be used to improve materials processing techniques on Earth, and in turn, products manufactured from these processes.
Early this evening Payload Commander Dr. Janice Voss performed a run of the flame ball experiment using a 4 percent hydrogen in air fuel mixture. “The rich fuel mixture matches the lean flammability limit of combustion on Earth,” said project scientist Dr. Karen Weiland of NASA’s Lewis Research Center in Cleveland, Ohio.
Voss’ sparking attempt resulted in eight flame balls. By studying flame balls, scientists hope to understand the physics of near-limit combustion, thereby leading to the design of leaner-burning fuels and improvements in engine efficiency - along with reduced emissions. The Structure of Flame Balls at Low Lewis-number experiment is led by Dr. Paul Ronney of the University of Southern California in Los Angeles.
This afternoon, Payload Specialist Dr. Roger Crouch performed the Bubble Drop and Non-linear Dynamics Experiment led by Dr. L.G. Leal of the University of California at Santa Barbara. During the experiment, Crouch deployed a bubble into the center of a water-filled container and then flattened it. On the ground the science team measured the bubble’s movement as the shape of the bubble changed--revealing mechanical properties of the bubble under large forces or distortions. Later, Crouch will deploy two bubbles and try to create one bubble from the two--shedding light on bubble control and manipulation. Results of the bubble experiment could lead to techniques that eliminate or counteract the complications that bubbles cause during materials processing.
Processing of a germanium sample to study diffusion processes in molten semiconductors ended this morning when the control thermocouple, or temperature sensor on the sample, malfunctioned. The sensor inadvertently told the furnace to heat the sample beyond the high temperature limit which caused the Large Isothermal Furnace to shut itself off. The furnace is designed to monitor temperature and will shut off automatically if a sample reaches a certain temperature. The science team on the ground says the Large Isothermal Furnace is operating normally, and are assessing the control thermocouple which is part of this particular sample run. The orbiter crew initiated another scheduled sample run of the experiment at 5:15 p.m. -- after the furnace had cooled down. This run is proceeding normally.
Ahead, Voss will conduct another run of the flame ball experiment and Crouch will continue the bubble experiment.
The next scheduled Public Affairs status report will be issued at approximately 6 a.m., July 11.
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