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An advanced low heat rejection engine concept has been selected based on a trade-off between thermal insulating performance and available technology. The engine concept heat rejection performance is limited by available ring-liner tribology and requires cylinder liner cooling to control the piston top ring reversal temperature. 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 tribological system is composed of chrome oxide coated cylinder, M2 steel top piston ring, M2 steel valve guides, and an advanced polyol ester class lubricant.

Significant reductions in valve and valve-seat insert wear have been demonstrated with the use of advanced materials for natural gas fueled engines. Total valve and insert wear was reduced by a factor of 10. It was demonstrated that the seat insert wear can be completely eliminated by using ceramic materials. All wear is then limited to the valve seat-face. The direct benefits to users of natural gas engines with advanced technology valve system materials can include reduced operating costs, greater convenience, and improved availability.

An advanced low heat rejection engine concept has successfully completed a 100 hour endurance test. 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. The tribological system was composed of a ceramic chrome oxide coated cylinder liner, chrome carbide coated piston rings and an advanced polyolester class lubricant. The top piston compression ring Included a novel design feature to provide self-cleaning of ring groove lubricant deposits to prevent ring face scuffing. The prototype test engine demonstrated 52 percent reduction in radiator heat rejection with reduced intake air aftercooling and strategic forced oil cooling.

Significant headway has recently been achieved in advanced high-temperature component design. Progress has been made in selecting a highly effective thermal insulating design composed of a titanium alloy piston with 1.0 mm thermal barrier coating which provides the same level of insulating effectiveness as a ductile iron piston with 2.5 mm coating. 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. Other benefits of the titanium alloy piston include low weight and increased high temperature strength. Thermal rig testing has been completed on several plasma-sprayed zirconia coatings and a critical durability threshold thickness of 1.25 mm has been identified. In addition, zirconia coatings and chrome-oxide-densified Eirconia coatings have been screened in a small bore diesel engine.