TransForum Vol. 3, No. 3

ULTRA-TOUGH CARBON COATINGS ARE FINDING MANY UNDERHOOD USES

More trucks are in use today than ever before, and even though diesel truck emissions have been greatly reduced over the years, further cuts are needed. The U.S. Environmental Protection Agency (EPA) has scheduled more restrictive emissions quotas for 2004 and proposed even tougher standards for 2007. Meeting such strict standards will mean reducing the sulfur content of diesel fuel and developing more advanced engine and emission-control technologies.

The impact of the EPA mandates will fall heaviest on diesel fuel-injection components, particularly injectors and fuel pumps. Fuel injectors, which already operate at 20,000 psi, will be expected to function at pressures of at least 30,000 psi and perhaps even 45,000 psi. Because an injector thrusts fuel into a cylinder by means of a plunger sliding inside a barrel, higher pressures mean smaller clearances between the two components, leading to reliability and durability issues. The main concerns involve wear and scuffing. Reducing the sulfur content of diesel fuel heightens the probability of wear and scuffing failures because there is less sulfur present to lubricate contacting surfaces with a slippery film of iron sulfide.

Argonne was among the first research organizations to offer a solution to higher injection pressures and reduced sulfur levels with its near-frictionless carbon coating technology. There are now many commercial diamond-like carbon coatings in the marketplace, but Argonne's ultra-hard films remain among the best in wear resistance and low-friction characteristics. "Our coatings exhibit the best friction coefficients in an inert atmosphere and the lowest coefficients that I have seen for dry sliding in air," says George Fenske, ANL's Tribology Section Manager. "They also have shown a very high resistance to scuffing."

Argonne is working with CemeCon to adapt the company's production-scale deposition system to coat components with near-frictionless carbon films.

Argonne's Tribology Section is working with Diesel Technology Corp. to develop near-frictionless carbon coatings for the company's heavy-duty diesel fuel-injector plungers. The results have been so promising that the Argonne group has begun focusing on coating the plungers and other automotive components on a commercial scale. Argonne has also entered into a Cooperative Research and Development Agreement (CRADA) with CemeCon to adapt the company's CC800/9 deposition system for coating components in 1,000- to 3,000-piece batches.

Fuel-injector plungers are by no means the only emerging application area for Argonne's coating technology. The group is also working with companies that are interested in coating critical surfaces in fuel pumps, hydraulic fluid pumps, and even heavy-duty truck axles. Fenske and his colleagues are also investigating using the coatings on fuel injector tips, cams, and turbocharged rotors. Yet another new application involves coating components in compressors designed to force air through fuel cells. "Many of these systems have components that cannot have any organic lubricant on them," Fenske explains. "Under those conditions, frictional losses can be quite high without an inert, low-friction coating like ours."

Perhaps the most exciting new area for the group involves the prospect of developing ultra-hard, low-friction coatings for micromachines. The group hopes to begin working with scientists from Northwestern University on nanotech devices that would gather information about engine performance while operating inside the running engines.

The group continues to maintain a strong commitment to basic research. Its members are now working at Argonne's Advanced Photon Source (APS) to gain a fundamental understanding of how lubricants interact with surfaces. The high brilliance of the APS enables them to do tests with oil films present; other techniques require that oil be removed. The group plans to eventually conduct dynamic tests under realistic loads and stresses at the APS.