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The U.S. Army Tank-Automotive Command is developing a future high power, low heat rejection military diesel engine. Performance requirements for the engine result in a predicted cylinder wall temperature of 560°C at the top piston ring reversal location. Thermal stresses imposed on the lubricant will therefore be unusually severe. Midwest Research Institute is developing the tribological system for this engine. A new general concept for high temperature diesel engine lubrication has been formulated. Our concept includes advanced synthetic liquid lubricants, solid lubricant additives, and self-lubricating materials. The lubricants, additives, and materials that have been selected for initial laboratory and engine evaluations of the concept are reported here.

Contrary to the thick thermal barrier coating approach used in adiabatic diesel engines, the authors have investigated the merits of thin coatings. Transient heat transfer analysis indicates that the temperature swings experienced at combustion chamber surfaces depend primarily on material thermophysical properties, i.e., conductivity, density, and specific heat. Thus, cyclic temperature swings should be alike whether thick or thin (less than 0.25 mm) coatings are applied, Furthermore, thin coatings would lead to lower mean component temperatures and would be easier to apply than thick coatings. The thinly-coated engine concept offers several advantages including improved volumetric efficiency, lower cylinder liner wall temperatures, improved piston-liner tribological behavior, and improved erosion-corrosion resistance and thus greater component durability.

High thermal stresses in the cylinder heads of low heat rejection (LHR) engines can lead to low cycle fatigue failure in the head. In order to decrease these stresses to a more acceptable level, novel designs are introduced. One design utilizes scallops in the bridge area, and three others utilize a high-strength, low thermal conductivity titanium faceplate inserted into the firedeck (combustion face) of a low heat rejection engine cylinder head. The faceplates are 5mm thick disks that span the firedeck from the injector bore to approximately 10mm outside of the cylinder liner. Large-scale finite element models for these four different LHR cylinder head configurations were created, and used to evaluate their strength performance on a pass/fail basis. The complex geometry of this cylinder head required very detailed three-dimensional analysis techniques, especially in the valve bridge area. This area is finely meshed to allow for accurate determination of stress gradients.

A large scale, high resolution, finite element methodology for analysis of generic thermomechanical behavior of complex, low heat rejection engine components has been developed. This paper describes this process and presents an example evaluation of a low heat rejection cylinder head. Because of symmetry considerations, a one cylinder section of the head was modeled. However, the geometric nature of this cylinder head section required very precise three-dimensional analysis techniques. The completed three-dimensional model contains 40,696 elements and 48,536 nodes. The results of this example model show high stresses at the valve bridge and injector bore. These stresses result from a constrained thermal expansion of the head, and are generally compressive and radial in nature. A comparison of three different material types indicated that two of the three exceeded, and one was below the elastic limit.

Even under steady state operating conditions, the pressure variation in individual cylinders, and the corresponding gas-pressure torque are subjected to small random fluctuations from cycle to cycle. The gas-pressure torque of a cylinder may be expressed as a sum of harmonically variable components, each harmonic being affected by these fluctuations. A probabilistic model of the vector interpreting such a harmonic component is developed and used to determine the statistical parameters of the resultant random vector representing the corresponding harmonic order of the engine torque. At the low frequencies of the lowest harmonic orders of the engine torque the crankshaft behaves like a rigid body. This behavior permits to correlate the statistical parameters of the same harmonic components of the resultant torque and of the measured engine speed. This correlation is proved by experiments and used to identify faulty cylinders.

The non-uniform character of the torque produced by a reciprocating I.C. engine is reflected in the cyclic variation of the crankshaft's speed. Because the crankshaft is an elastic structure, its response to the different harmonic components of the torque is different and changes with engine speed. The lowest harmonic components of the engine torque do not excite torsional vibrations and correlate fairly well with the corresponding harmonic orders of the crankshaft's speed. Based on a random vector model of the harmonic components of the gas-pressure torque, a statistical correlation is obtained between amplitudes and phases of the same harmonic component of the gas-pressure torque and of the crankshaft's speed. The lowest major harmonic order determines the average IMEP of the engine and the half-order detects if a cylinder is a lesser contributor to the total engine output and identifies the deficient cylinder.

The paper tries to establish the possible correlations between the fluctuations of the angular motion of the crankshaft -which may be easily measured-with the variations of the pressure time-histories in the engine's cylinders. The model of the dynamic system of an engine shafting and the appropriate computing code are validated by comparison with measured angular motion of the front-end of the crankshaft. The algorithm of the code - based on the transfer matrix method - is then reversed in order to obtain the harmonic components of the exciting torques acting along the crankshaft from the harmonic components of the motion of the free-end of the crankshaft. Different ways of performing this task and the influence of nonuniform cylinder contributions are investigated and discussed.

This paper documents the successful operation of a modified Cummins T46 turbocharger with a ceramic rotor. This turbocharger is modified to incorporate a 4.6 inch diameter ceramic turbine rotor (pressureless sintered silicon nitride) on the hot end. These results document the most complete ceramic turbine rotor performance map, for a large ceramic turbocharger rotor, available to date.

In marine propulsion systems with direct-coupled two-stroke large diesel engines, the angular position of the propeller with respect to the crankshaft remains unchanged during the whole operation of the engine. The interference between major harmonic orders of the engine torque is avoided by choosing a number of blades, different from any divisor of the cylinder number. However, interferences between other harmonic orders of the engine torque and the major harmonic order of the propeller torque -which is equal to the number of blades- may increase the amplitude of torsional vibrations. The paper shows that there is an optimum Phasing between crankshaft and propeller for which a decrease, up to 20%, of the dynamic shear stress of the shafting -in comparison with the worst possible phasing- may be achieved. This results points out the importance of being able to calculate, in the design stage, the best phasing of engine and propeller

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.

A high output experimental single cylinder diesel engine that was fully coated and insulated with a ceramic slurry coated combustion chamber was tested at full load and full speed. The cylinder liner and cylinder head mere constructed of 410 Series stainless steel and the top half of the articulated piston and the cylinder head top deck plate were made of titanium. 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. In spite of the high boost pressure ratio of 4:1, the pressure charged air was not aftercooled. No deterioration in engine volumetric efficiency was noted. At full load (260 psi BMEP) and 2600 rpm, the coolant heat rejection rate of 12 btu/hp.min. was achieved. The original engine build had coolant heat rejection of 18.3 btu/hp-min and exhaust energy heat rejection of 42.3 btu/hp-min at full load.

The instantaneous frictional torque (IFT) of many components of a single cylinder diesel engine was determined by considering the forces acting on each component and the resulting change in the angular velocity. The IFT for the basic system, consisting of the crankshaft with the flywheel and oil pump, was first determined. The effect of adding each of the following to the basic system was determined: balancer shaft, cam shaft, piston with different ring combinations, inlet valve, exhaust valve and fuel injection pump. All the tests were conducted without gas pressure in the cylinder in a coast down mode. The results indicated the contribution of each component in the total frictional torque and its mode of lubrication. The energy absorbed by the valve springs and released back to the system was clearly Identified. The effect of speed on IFT and energy lost in friction was determined.

This paper deals with the analysis of heat release characteristics of an insulated turbocharged, six cylinder, DI contemporary diesel engine. The engine is fully insulated with thin thermal barrier coatings. Effect of insulation on the heat release was experimentally verified. Tests were carried over a range of engine speeds at 100%, 93%, 75% and 50% of rated torque. Fuel injection system was instrumented to obtain injection pressure characteristics. The study shows that rate of heat release, particularly in the major portion of the combustion, is higher for the insulated engine. Improvement in heat release and performance are primarily attributed to reduction in heat transfer loss due to the thin thermal barrier coating. Injection pressure at the rated speed and torque was found to be 138 MPa and there was no degradation of combustion process in the insulated engine. Improvements in BSFC at 93% load are 3.25% and 6% at 1600 and 2600 RPM, respectively.

Significant progress has been achieved in the development of advanced high-temperature, insulated, in-cylinder components for high-power-output miliraty diesel engines. Computer aided modeling and small-bore engine component testing have both been utilized extensively during the exploratory development process. Specific insulated optimal designs for the piston, cylinder headface, and cylinder liner have been identified. 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.

High-pressure fuel injection combustion is being applied as an approach to increase the power density of diesel engines. The high-pressure injection enables higher air utilization and thus improved smoke free low air-fuel ratio combustion is obtained. It also greatly increases the injection rate and reduces combustion duration that permits timing retard for lower peak cylinder pressure and improved emissions without a loss in fuel consumption. Optimization of these injection parameters offers increased power density opportunities. The lower air-fuel ratio is also conducive to simpler air-handling and lower pressure ratio turbocharger requirements. This paper includes laboratory data demonstrating a 26 percent increase in power density by optimizing these parameters with injection pressures to 200 mPa.

The cylinder block of a high-speed marine diesel engine is a complex structure subjected to a complex loading. The design optimization of the cylinder block requires a reliable Finite Element Model (FEM), capable to predict, with a reasonable accuracy, the actual strains and stresses. The experimental investigation presented in the paper is meant to provide the necessary information for a better estimation of the boundary conditions and the validation of the FEM of the cylinder block. In order to obtain an image of the stress field in the cylinder block, a system of 10 strain gauge rosettes have been placed at significant locations on the cylinder block. The temperature at the location of the rosettes was measured with an optical pyrometer and a method has been developed to calculate this temperature using the measured strain. A fairly good agreement was obtained between the measured and the calculated temperatures during the cooling of the engine.

An experimental method for determining the Instantaneous Frictional Torque (IFT) using pressure transducers on every cylinder and speed measurements at both ends of the crankshaft is presented. The speed variation measured at one end of the crankshaft is distorted by torsional vibrations making it difficult to establish a simple and direct correlation between the acting torque and measured speed. Using a lumped mass model of the crankshaft and modal analysis techniques, the contributions of the different natural modes to the motion along the crankshaft axis are determined. Based on this model a method was devised to combine speed measurements made at both ends of the crankshaft in such a way as to eliminate the influence of torsional vibrations and obtain the equivalent rigid body motion of the crankshaft. This motion, the loading torque and the gas pressure torque are utilized to determine the IFT.

The increased interest for using alternative fuels in modern diesel engines requires better combustion control to achieve safe and efficient operation with fuels characterized by different physical and chemical properties. Knowing the ignition delay and the cylinder peak pressure will allow adapting the injection strategy, mainly injection timing to maintain good engine efficiency when operating with different alternative fuels. The use of the measured instantaneous crankshaft speed to estimate peak cylinder pressure and ignition delay is very attractive because speed is already a parameter in the ECU of the engine. Based on models using powertrain dynamics, the paper presents the development of several techniques using the measured speed to estimate the main combustion parameters for single cylinder and four cylinder diesel engines.

The simulation of I.C. Engines operation, especially during transients, requires a fairly accurate estimation of the internal mechanical losses of the engine. The paper presents generic friction models for the main friction components of the engine (piston-ring-liner assembly, bearings and valve train), considering geometry of the engine parts and peculiarities of the corresponding lubrication processes. Separate models for the mechanical losses introduced by the injection system, oil and water pumps are also developed. All models are implemented as SIMULINK modules in a complex engine simulation code developed in SIMULINK and capable to simulate both steady state and transient operating conditions. Validation is achieved by comparison with measurements made on a four cylinder, common rail diesel engine, on a test bench capable to run controlled transients.

The experimental emissions testing of a turbocharged six cylinder Caterpillar 3116 diesel engine converted to the Miller cycle operation was conducted. Delayed intake valve closing times were also investigated. Effects of intake valve closing time, injection time, and insulation of piston, head, and liner on the emission characteristics of the Miller cycle engine were experimentally verified. Superior performance and emission characteristic was achieved with a LHR insulated engine. Therefore, all emission and performance comparisons are made with LHR insulated standard engine with LHR insulated Miller cycle engine. Particularly, NOx, CO2, HC, smoke and BSFC data are obtained for comparison. Effect of increasing the intake boost pressure on emission was also studied. Poor emission characteristics of the Miller cycle engine are shown to improve with increased boost pressure. Performance of the insulated Miller cycle engine shows improvement in BSFC when compared to the base engine.