Understanding Combustion On Earth And In Space

After this procedure was finished, on 5 April Linteris started the LSP investigation, provided by Gerard Faeth of the University of Michigan at Ann Arbor, which was designed to gather data on flame shapes, together with the quantities, temperatures and types of soot produced under various conditions. The experiment supported ongoing efforts to better understand how to control fires and help to limit the number of deaths on Earth from carbon monoxide poisoning associated with soot. A frightening demonstration of how fire behaves in space had already occurred just two months before Columbia's launch.

In February 1997, NASA astronaut Jerry Linenger was entering his fifth week of a planned four-month stay on board the Russian Mir space station, when an accidental fire - triggered by an oxygen-regeneration canister - burned for 10 minutes, filled the complex with smoke and forced the entire six-man crew to don breathing masks. Linenger later commented that he was ''stunned'' at how rapidly the smoke spread. The experience, said Joel Kearns of NASA's microgravity office, ''just heightens our concern that we understand this phenomenon both in space and on Earth''.

''Soot has a lot of negative attributes and that's why we're concerned about it. It's a pollutant,'' said Gerard Faeth. ''It is harmful to public health. It is the major source of difficulties of unwanted fires in homes. Soot has carbon monoxide associated with it, which is toxic and in that role soot is responsible for the deaths of about 4,000 people a year in the United States and fire injuries of about 25,000.''

By 6 April, a mere two days into the mission, the experiment gave him his first glimpse of the concentration and structure of soot from a fire burning in microgravity. ''We've hit a home run: it's the first truly steady, non-buoyant flame that's been observed by anybody, anywhere on Earth,'' Faeth exulted. ''It's a real first and the pictures we saw today will probably find their way into textbooks of the future.''

Another major study in this area was the Droplet Combustion Apparatus (DCA), which occupied Voss during one of her early shifts on 5 April and housed a variety of experiments to investigate burning drops of different fuels and monitor conditions at the instant of their extinction. A significant amount of the energy produced around the world comes from burning fuels, Vedha Nayagam of Lewis Research Center said, and by studying them in space and comparing their data to theoretical models it was hoped to learn more about their chemical makeup.

Combustion of fuel droplets is an important element in heating materials-processing furnaces, homes and businesses, providing power by gas turbines and for car engines. Ultimately, it was expected that such understanding would enable the development of technologies to burn fuels far more efficiently, minimising pollutant quantities in the process. Inside the DCA, which filled one rack in the MSL-1 module, was the Droplet Combustion Experiment (DCE) which investigated the fundamental combustion aspects of isolated drops under different pressures and oxygen concentrations. Each drop varied between 2 and 5 mm in diameter.

In most practical combustion devices, liquid fuels are mixed with oxidisers and burned in the form of sprays. An essential prerequisite for an understanding of such 'spray combustion' and its application to the design of efficient and clean combustion systems is knowledge of the laws governing droplet combustion. In the absence of buoyancy-induced convection currents, a droplet ignited in microgravity burns with spherical symmetry and yields a simple, one-dimensional system capable of being very precisely modelled. Previous experiments using 'drop towers' at Lewis Research Center could only produce data for droplets up to 3 mm in diameter.

The microgravity environment on board the Spacelab module, on the other hand, provided scientists with an opportunity to better investigate the complicated interactions of physical and chemical processes during droplet combustion. As well as permitting experimentation with varying droplet sizes, it also became possible to study them over longer periods of time. During typical DCE activities, images of the burning droplets and surrounding flames were taken and processed to obtain precise data on their 'burn rates' and other characteristics, including phenomena surrounding the extinction process.

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