OAK RIDGE, Tenn. -- Heavy-equipment engines that operate around the clock in huge mine-haul trucks can be a pain in the neck if the engine valves fail in service. Researchers at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) have participated in the development of ceramic valves that offer longer life and better durability.
The ceramic valves were developed as part of the Ceramic Technology Project, an ORNL-led DOE Office of Transportation Technologies program begun in 1983 for the development of an industrial technology base to provide reliable and cost-effective, high-temperature ceramic components for applications in advanced heat engines. The three areas of the project were materials and processing, design methodology and life prediction analyses.
Through an ORNL-managed research and development contract in advanced ceramic manufacturing technology, Norton Advanced Ceramics Corp. (NAC), a division of Saint-Gobain/Norton Industrial Ceramics Corporation, is heading a development team to cost-effectively manufacture and test ceramic diesel valves. Detroit Diesel Corp. (DDC), also on this team, designed the valves. Then, NAC's responsibility is to develop the cost-effective manufacturing technology, and DDC is to test the valves in their engines.
In related projects, ORNL and DDC entered into a cooperative research and development agreement (CRADA) to design the valves and ORNL initiated a project to develop life-prediction methodology using algorithms originally developed for ceramic turbine engines.
The problem with conventional, metallic valves is that the vehicles in which they operate are driven continuously in adverse conditions and mountainous terrain.
"Ceramic valves are best suited for diesel mining trucks that carry enormous loads in severe environments -- places like Peru and Chile," said Arvid Pasto, director of the High Temperature Materials Laboratory (HTML) in the Metals and Ceramics Division at ORNL. "In addition, we've found that ceramics are better suited for marine environments, such as in some types of diesel-engine powered boats."
The researchers discovered early on the reason for the high failure rate of the metallic valves.
"Metallic valves fail due to corrosion caused by sulfur in the fuel," said D. Ray Johnson, program manager of ORNL's Ceramic Technology Project. "The industry people call the phenomenon 'guttering.' The grooves shorten the effective lifespan of the valves."
The first goal of the Ceramic Technology Project, the production of reliable ceramics for engines, was completed in 1993. It was met by the completion of the first phase of the program plan, but further work was needed to reduce the cost of the ceramic valves.
To help in the process of making the valves cost-effective for manufacturers, the Revised Program Plan for Cost-Effective Ceramics for Heat Engines was developed and implemented in 1993.
"As for price, it's not advantageous for a manufacturer to buy the ceramic valves, right now," said Pasto, who is also serving as the technical monitor for the contract between ORNL, DDC and NAC. "Even though they are more durable, it's just not as cost-effective as using special-alloy metallic valves. Some time in the future I believe ceramic valves will sell for about the same price, though."
In the past, the biggest problem, other than cost, was the unreliability of the ceramic valves. Now, that problem has been overcome because ceramic valves have passed the reliability and durability test criteria of the conventional valves.
"Four valves are currently running in an engine in a mine haul truck and have accumulated over 2,000 hours already," Pasto said. "If the ceramic valves were going to fail, they likely would have failed in the first 1,000 hours."
Static and cyclic tests conducted by Jim Corum of ORNL's Engineering Technology Division have proven that the valves can tolerate more severe conditions than metallic valves.
"There is not a problem with holding up under high temperatures as with the metallic valves," Corum said. "We built a machine that hydraulically applies combustion pressure to the valves and tests them both cyclically and statically. The valves are put under greater loads during the tests than they would have to endure in regular engine-operating conditions.
"Our tests proved that ceramic valves had very good margin against failure. The tests gave the CRADA partner, DDC, confidence and validated our predictions for the lifespan of the valves."
In addition, ORNL researchers are developing methods for forecasting how long the ceramic valves will last. Andy Wereszczak, staff development engineer at ORNL, is adapting computer codes for predicting the lifetime of the valves. This includes performing two-and three-dimensional life prediction analyses along with many static and fatigue failure tests.
The codes were initially developed for gas turbine components, but Wereszczak adapted them for diesel components. The results have been encouraging because they indicate a high level of structural integrity for the ceramic valves.
ORNL, one of DOE's multiprogram national research and development facilities, is managed by Lockheed Martin Energy Research Corporation.