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The future of maintaining a superior mobile military ground vehicle fleet rests in high power density propulsion systems. As the U.S. Government desires to convert its powerplant base to heavy fuel operation, there arises the opportunity to incorporate new advanced materials into these heavy fuel engines. These newer materials serve the purpose of decreasing powerplant weight and develop new component designs to take advantage of improved strength and temperature capability of those materials. In addition, the military continues the effort for a non-watercooled Low Heat Rejection (LHR) diesel engine. This type of engine demands the use of ceramic and advanced ceramic composite material hardware. Furthermore, today's higher pressure fuel injection systems, coupled with reduced air/fuel ratio as a means of increasing horsepower to size and weight, will require thermal protection or change in material specification for many of the engine's components.

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. 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. Research and development (R&D) and analysis were conducted on aluminum alloy piston for high output turbocharged diesel engine coated with TBC.

A proprietary high hardness carbon thin film coating has been used to enhance the performance capability of engine components for racing applications. Coating properties, including high surface conformance, high adhesion, high hardness, flexibility, and low friction produce benefits for metal components in scuffing and impact applications. Methods to validate the coating's properties include surface topography, adhesion testing, hardness and friction coefficient measurements, and wear rate testing. Hardness testing is accomplished with a nano-indentation tool capable of isolating the coating's properties from those of the substrate, thereby minimizing measurement variations among substrates of varying hardness. The nano-indentation tool also measures elastic properties. Traditional lubricated test methods are used to demonstrate differences in friction and wear rates with coated surfaces compared to uncoated substrates.

This paper presents tribological modeling, experimental work, and validation of tribology parameters of a single cylinder turbocharged diesel engine run at various loads, speeds, intake boost pressures, and cylinder liner temperatures. Analysis were made on piston rings and liner materials, rings mechanical and thermal loads, contact pressure between rings and liner, and lubricant conditions. The engine tribology parameters were measured, and used to validate the engine tribology models. These tribology parameters are: oil film thickness, coefficient of friction between rings and liner, friction force, friction power, friction torque, shear rate, shear stress and wear of the sliding surfaces. In order to measure the oil film thickness between rings and liner, a single cylinder AVL turbocharged diesel engine was instrumented to accept the difference in voltage drop method between rings, oil film, and liner.

Experimental results focused towards developing tribological surface coatings coupled with liquid lubricant boundary layer effects, for advanced high temperature military diesel engine applications are presented. The primary focus of this work is in the area of advanced, low heat rejection (LHR) high output diesel engines, where high temperature boundary lubrication between the piston ring and the cylinder liner wall surface is critical for successful engine operation. The target temperature focused upon in our research is an operating top ring reversal (TRR) temperature of approximately 538°C. The technology advancement used for this application involves treating porous iron oxide/titanium oxide (Fe2O3/TiO2) and molybdenum (Mo) based composite thermal sprayed coatings with chemical binders to improve coating strength, integrity, and tribological properties. This process dramatically decreases open porosity to form an almost monolithic appearing coating at the surface1.

Adiabatics, Inc., with the support of the U.S. Army Tank Automotive Research & Development Engineering Center (TARDEC) has developed a low cost, durable ceramic composite cylinder bore coating for diesel engines operating under severe conditions. This bore coating is a ceramic composite consisting primarily of Iron Oxide, Iron Titanate and Partially Stabilized Zirconia. It is applied by unique chemical thermal bonding technology developed at Adiabatics, Inc. and is referred to as Low Temperature Iron Titanate (LTIT). This coating has been tested against a wide range of cylinder bore treatments ranging from hard chrome plate to hard Nickel Silicon Carbide (NikaSil) and found to provide a superior sliding wear surface. It is superior because it is compatible against most common piston ring materials and coatings.

Valve wear has been identified as a major durability problem in natural gas fueled reciprocating engines. Over the years, progress has been made to alleviate this problem through improved valve design and materials development. Recently high performance ceramics have shown promise for wear component applications. This paper presents the results of a valve train component materials investigation supported by the Gas Research institute. Testing tools and methods are described. The testing program culminated in a 300 hour component test in a full size turbocharged natural gas engine. Results of the engine test appeared to confirm preceding laboratory tests. Sintered silicon nitride valve seat inserts and Stellite 6 coated 21-12 stainless steel valves appeared to be the most promising material combination evaluated.

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.

The trend toward lighter vehicles for improved performance has recently introduced the use of aluminum and plastic materials for vehicle bodies and drive trains. In particular, the aluminum alloy block for engine application is certain to reappear. The soft aluminum cylinder liner will require additional treatment before acceptance. Three possible approaches appear to solve the aluminum cylinder liner dilemma. These approaches are: 1. Use of high silicon aluminum such as the 390 aluminum. 2. Insert or cast steel liners into the aluminum engine block. 3. Ceramic coat the low cost standard aluminum engine block. Each has known advantages and disadvantages. It is the purpose of this paper to present the merits of Option 3, the ceramic coated aluminum cylinder bore from the standpoint of low weight, cost, and tribological effectiveness. The advantages of approaches (1) and (2) are obvious. High temperature after treatment of the ceramic engine components is not required.

The high temperature tribology issue for uncooled Low Heat Rejection (LHR) diesel engines where the cylinder liner piston ring interface exceeds temperatures of 225°C to 250°C has existed for decades. It is a problem that has persistently prohibited advances in non-watercooled LHR engine development. Though the problem is not specific to non-watercooled LHR diesel engines, it is the topic of this research study for the past two and one half years. In the late 1970s and throughout the 1980s, a tremendous amount of research had been placed upon the development of the LHR diesel engine. LHR engine finite element design and cycle simulation models had been generated. Many of these projected the cylinder liner piston ring top ring reversal (TRR) temperature to exceed 540°C[1]. In order for the LHR diesel to succeed, a tribological solution for these high TRR temperatures had to be developed.