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Things That Efficiently Go Ka-Bump in the Night

November 04, 1996|KATHLEEN WIEGNER

Anyone who has heard an older automobile make a "ka-bump, ka-bump" sound after the ignition is turned off has encountered a phenomenon known as pulse combustion.

Although this "dieseling" is not desirable in cars, pulse combustion is actually an inherently efficient process: Once it is sparked, it is self-sustaining, drawing in gas in a pulsating pressure wave and automatically firing on the order of 100 times a minute. Some top-of-the-line domestic water heaters and furnaces using pulse combustion show thermal efficiencies of 96%, well above those of conventional systems.

Now researchers at Sandia National Laboratories in Livermore, Calif., have received a patent on a form of pulse combustion that is not only efficient but also environmentally friendly. The process minimizes emissions by mixing fuel and air before burning, and by keeping the fuel-air ratio lean. Both the fuel and air are separate until the valve opens.

Both gases mix after they pass through the valve, which minimizes fuel-rich combustion, a major source of pollutants. Sandia's patented approach creates only five parts per million of nitrogen oxide, a pollutant that contributes to smog. It also emits very low amounts of carbon monoxide.


Salmonella Probe: The spread of salmonella from raw eggs has led egg producers to begin cleaning up their act. Raw eggs are disinfected by washing them with a detergent and then dipping them in a wax solution to seal eggshell pores. But professor Shmuel Yannai at Technion-Israel Institute for Technology argues that the real danger of salmonella transmission comes from the eggshells themselves, not the interior of the egg.

Only one in 10,000 to 20,000 eggs is infected with salmonella, Yannai says. More frequently, bacteria found on the shell surface infect the egg when it is cracked open or when uncooked food is prepared on contaminated surfaces. In fact, he says, the current method of disinfecting eggs actually dissolves the shell's external protective layer and facilitates the bacteria's entry into the egg through the shell.

Yannai's alternative is a low concentration of ozone gas. An "ozonator" he developed at Technion generates an ozone-and-air mixture that kills pathogens as well as bacteria and fungal spores on the eggshells. The ozone does not penetrate the edible parts of the egg and spontaneously breaks down into common oxygen within a matter of minutes. Ozone-disinfected eggs will be marketed in Israel in the near future and are expected to cost only a few cents more than those conventionally disinfected.


A Flashier Form of Welding: It's often hard for soldiers in the field to lug around a welding torch in order to repair their equipment. Now two researchers at Johns Hopkins University may have solved the problem with a piece of foil and a match.

By slipping a metallic film, as thin as aluminum foil, between the broken parts and igniting it with a match, a soldier can create a sturdy seal and be on his way.

The foil is created by microscopic layering of two elements in alternating rows. The researchers choose elements that create strong bonds--nickel and aluminum for example. When a match flame or the spark from a 9-volt battery is applied to the foil, the molecules quickly bond, triggering an exothermic reaction that causes the entire sheet of foil to ignite, quickly raising its temperature to 2,900 degrees Fahrenheit.

Because the heat erupts and ends so quickly, it can bond objects at their surface without damaging the rest. And because the process uses no oxygen, it can be used under water or in airless outer space.

Flashy foils won't replace conventional welding in the near future because they are expensive and difficult to make. But in certain military and industrial applications, the additional cost could be justified.

Freelance writer Kathleen Wiegner can be reached at

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