The U.S. Navy and U.S. Air Force (USAF) in collaboration with ESTCP are demonstrating a novel protective coating that will reduce wear on compressor airfoils in gas turbine engines, significantly increase fuel efficiency, and reduce overhaul and maintenance requirements. Additional benefits for the Department of Defense (DoD) include substantial cost savings and a reduction in its overall industrial footprint.

DoD operates in harsh environments that accelerate the erosion of the compressor airfoils in gas turbine engines used in fixed and rotary-winged aircraft as well as certain ground vehicles. Erosion of the compressor  airfoils can increase fuel consumption by as much as 5 percent and increase the frequency of repairs required to keep engines in service. The resulting increase in maintenance and repair leads to an increase in industrial waste streams associated with the life cycle of the engine. Additionally, engines with worn compressor airfoils generally produce between 10 and 25 percent more nitrogen oxide (NOx) emissions than a new or rebuilt engine.

To address these concerns, Naval Air Systems Command (NAVAIR) and the USAF with oversight by the Office of the Secretary of Defense are demonstrating a new erosion/corrosion resistant coating. The erosion/corrosion resistant coating, developed by MDS Coating Technologies (MCT), is a multilayer ceramic-metallic matrix that is applied in a vacuum via a cathodic arc, physical vapor deposition (CAPVD) process, which is a proven coating process. Design elements in the MCT erosion/corrosion resistant coating allow it to survive in the harsh environments of a gas turbine engine and withstand specific failure mechanisms. It is the first erosion/corrosion resistant coating in the industry to pass corrosion tests successfully on a repeatable basis.

Under this ESTCP project, the MCT erosion/corrosion resistant coating is being demonstrated on several types of engines including the T56 used in the C-130 and E-2 aircraft, the AGT1500 used in the Abrams M1A tank, and the F414 used in the F/A-18 aircraft. The coatings for the T56 engine completed a sand ingestion test comparing the performance and hardware condition of an uncoated and coated compressor. The coating for the AGT1500 engine will complete a similar engine sand ingestion test. Computer performance modeling comparisons of coated and uncoated engines will also be conducted on the fixed-wing engine applications. The F414 engine will rely solely on modeling and analyses based on field data to determine potential fuel savings for aircraft such as the F/A-18.

The T56 sand ingestion test results demonstrated three times greater performance retention for the coated compressor versus the uncoated compressor and significant erosion protection for the coated compressor airfoils. The sand ingestion test for the AGT1500 engine is scheduled to be completed in mid-2012.

Based on the results from the T56 sand ingestion test, it is expected that DoD will realize significant benefits in future operations with coated compressors. For example, the USAF and NAVAIR overhaul approximately 300 T56 engines per year with engine maintenance costs exceeding $200 million annually. It is expected that application of the erosion/corrosion resistant coating will increase average engine mean-time-between-repair and, hence, reduce annual maintenance costs and industrial waste by decreasing the number of engines inducted for repair and overhaul. Additionally, the coating has demonstrated up to 5 percent fuel savings in various tests.

Using a conservative 2 percent potential fuel savings, the USAF would realize approximately $12 million in annual fuel savings for its C-130 fleet. Similar benefits would be realized if the MCT erosion/corrosion resistant coating transitions into the programs using the AGT1500 and F414 engines. Further, operating at or near this peak efficiency throughout the T56-A-15’s operational cycle can potentially reduce engine exhaust pollutants such as NOx, SOx  and carbon dioxide by 5 to 15 percent.

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