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Thermal barrier coatings (TBC) are perceived as enabling technology to increase low heat rejection (LHR) diesel engine performance and improve its longevity. ...The state of the art of thermal barrier coating is the plasma spray zirconia. In addition, other material systems have been investigated for the next generation of thermal barrier coatings. ...In addition, other material systems have been investigated for the next generation of thermal barrier coatings. The purpose of this TBC program is to focus on developing binder systems with low thermal conductivity materials to improve the coating durability under high load and temperature cyclical conditions encountered in the real engine.

The low thermal conductivity of Titanium Alloy 6242 inherently provides a significant level of thermal resistance which effectively reduces the required coating thickness, reduces thermal stresses, and nearly eliminates coating thermal expansion mismatch. ...In addition, zirconia coatings and chrome-oxide-densified Eirconia coatings have been screened in a small bore diesel engine. ...The only coating which remained free of visual surface cracks was the chrome-oxide-densified coating. This paper will present the second year's results and future plans of the low-heat-rejection engine component technology development program for high output military engines sponsored by the U.S.

Tests were carried out over a range of engine speeds at full load for a standard metal piston and two pistons insulated with 0.5 mm and 1.0 mm thick ceramic coatings. The thinner (0.5 mm) ceramic coating resulted in improved performance over the baseline engine, with the gains being especially pronounced with decreasing engine speed. ...An experimental investigation of the effects of ceramic coatings on diesel engine performance and exhaust emissions was conducted. Tests were carried out over a range of engine speeds at full load for a standard metal piston and two pistons insulated with 0.5 mm and 1.0 mm thick ceramic coatings. ...In contrast, the relatively thicker coating (1 mm), resulted in as much as 6% lower thermal efficiency compared to baseline. On the other hand, the insulated engines consistently presented an attractive picture in terms of their emissions characteristics.

Densification or thermal sealing the plasma spray layer, a process developed on the project, improves the coating's tribological properties. These coating materials are awaiting to be tested in the single cylinder engine.

Titanium Alloy and Steel pistons were coated with various 1.25 mm thick thermal sprayed zirconia coatings. All of the coatings experienced failure by cracking except for the slurry densified coating. ...The designs all utilize thermal barrier coatings, titanium alloy, and interfacial air-gaps to provide thermal resistance. Finite element modeling including diesel cycle simulation has been utilized to screen and optimize material and design concepts relative to program objectives, while small-bore engine testing has been utilized to demonstrate component integrity. ...An improved slurry densified thermal barrier coating has been demonstrated by testing on a high temperature small-bore engine. Titanium Alloy and Steel pistons were coated with various 1.25 mm thick thermal sprayed zirconia coatings.

The piston concept is composed of a relatively low thermal conductivity titanium alloy type 6242 structural material and a 1.25 mm thick slurry densified thermal barrier coating. The piston material, structural configuration, and detail design features were selected through computer aided modelling and qualified through small-bore engine testing. ...Screening of plasma sprayed thermal barrier coatings was performed on a simple thermal test rig and final selection of a system was made through small-bore engine testing.

The cylinder liner, head plate and the piston crown were coated with ceramic slurry coating. An adiabaticity of 35 percent was predicted for the insulated engine. The top ring reversal area on the cylinder liner was oil cooled.

This engine concept is composed of a titanium piston, headface plate and cylinder liner insert with thermal barrier coatings. Monolithic zirconia valve seat inserts, and thermal barrier coated valves and intake-exhaust ports complete the insulation package.

The combustion chamber components were insulated with thermal barrier coatings. The engine components included a titanium piston, titanium headface plate, titanium cylinder liner insert, M2 steel valve guides and monolithic zirconia valve seat inserts.

These included: (1) the valve actuation system which included monolithic Silicon Nitride exhaust valves and clevis pins, (2) the fuel injection system which incorporated a monolithic Silicon Nitride injector needle valve, (3) the power transfer system design which included pistons with plasma sprayed thermal barrier coatings and (4) the air handling system which was modified to include abradable compressor and turbine housing coatings. ...These included: (1) the valve actuation system which included monolithic Silicon Nitride exhaust valves and clevis pins, (2) the fuel injection system which incorporated a monolithic Silicon Nitride injector needle valve, (3) the power transfer system design which included pistons with plasma sprayed thermal barrier coatings and (4) the air handling system which was modified to include abradable compressor and turbine housing coatings. The ACTIP engine successfully completed the 400 Hour cyclic durability test. Final inspection of the engine components at the completion of the test showed there were no problematic conditions which would have precluded continuation of testing.