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The slow road to ceramic engines.

The slow road to ceramic engines

Ceramic materials appear to have many of the properties necessary to improve the fuel efficiency of diesel engines. Unlike metals, they can withstand high temperatures without weakening, and they are good insulators. Ceramics, however, are brittle and may readily fracture or shatter. This failing has slowed the development of ceramic engines and engine parts. In recent years, most manufacturers and researchers have concentrated on developing ceramic parts for a few specific applications and for insulating an engine's cylinders to cut down heat losses.

Now a National Research Council study concludes that merely adding a layer of ceramic insulation improves fuel economy by only a few percent. "While the outlook for substantial gains in fuel economy was less encouraging than previously reported,' says mechanical engineer Phillip S. Myers of the University of Wisconsin in Madison, who chaired the study committee, "we found considerable potential for use of ceramics in other places in the engine besides insulating the cylinder.' Such applications, by lowering friction and by substituting lighter, harder materials for metals, could add up to significant savings. Myers and several members of his committee presented their conclusions last week at a seminar at the National Academy of Sciences in Washington, D.C.

What's needed is a systems approach, says committee member John H. Johnson of the Michigan Technological University in Houghton. "We need to integrate new technologies, materials and electronics. Together, that would have an impact on fuel economy.'

For instance, insulating an engine isn't the only way to minimize heat losses. Hot gases, instead of escaping in the exhaust, could be diverted to drive a turbine and increase the engine's power. Furthermore, by keeping heat losses to a minimum, an engine can run at a higher temperature, using fuel more efficiently. But even if higher operating temperatures are achieved, few lubricants can survive long periods at such temperatures, says Myers. "We need to develop new lubricants.'

Despite the difficulties in developing efficient diesel engines, the study recommends that research on "low heat rejection' engines continue. The U.S. Army, which along with the Department of Energy sponsored the study, has 25,000 tracked vehicles, such as tanks, and 250,000 trucks and other wheeled vehicles. A fuel-economy improvement of 5 to 10 percent, combined with the energy savings from operating a smaller cooling system, would allow greater design flexibility. Vehicles with improved diesel engines would likely be more reliable and better able to survive combat conditions.

The situation is more complicated for cars and light trucks that aren't powered by diesel engines. Raising operating temperatures in conventional engines increases the likelihood of engine knock (SN: 9/13/86, p.165).

"Engine developments come not as revolutions but as small-increment changes,' says Myers. The problem is that, unlike Japan and several European countries, "we [the United States] don't have a national, coordinated effort,' he says. "And we don't have quite the innovative spirit seen abroad.'

Adds Johnson, "We've got the technologies. It's matter of putting them all together. That takes a great commitment of resources.'
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Title Annotation:diesel engine research
Author:Peterson, Ivars
Publication:Science News
Date:Oct 3, 1987
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