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Selective reinforcement of squeeze-cast aluminum pistons by fiber matrix inserts is a method of improving high temperature strength in piston zones subject to severe thermal and mechanical loads in highly loaded diesel engines. An investigation was carried out into the effects of selective fiber-matrix reinforcement on the thermal and stress state of an aluminum piston for a heavy-duty truck diesel engine application. Specifically, effects of geometry of the reinforced zone (fiber matrix), fiber density in the matrix, fiber orientation and piston combustion bowl shape were sought. Thermal and structural finite element analysis of the configurations were carried out. Thermal analyses were fully coupled to a simulation of a highly rated heavy-duty diesel.

This paper describes a comprehensive model of piston skirt lubrication, developed for use in conjunction with piston secondary dynamic analysis, to accurately characterize the effects of the skirt-cylinder oil film on piston motions. The model represents both hydrodynamic and boundary lubrication modes and applies an asperity contact pressure when surfaces are in close proximity with each other. In addition to skirt dimensions and surface roughness properties, the circumferential extent of lubrication, an arbitrary skirt profile and bore distortion are specifiable inputs to the model. The model is also extended to represent the oil starvation at the cylinder end of the skirt by allowing the axial extent of lubrication on the skirt surface to vary circumferentially and with time to satisfy continuity of oil.

This paper describes a general model for the analysis of secondary motions in conventional and articulated piston assemblies. The model solves for the axial, lateral and rotational departures in positions and motions from the nominal kinematics, resulting from clearances within the piston assembly and also between the piston assembly components and the cylinder. The methodology allows the characterization of conventional and articulated piston secondary motions in the thrust plane of the cylinder. Motions of the piston, pin, rod and (for articulated pistons) skirt are separately calculated, by integrating equations of motion for individual components and dynamic degrees of freedom. Various configurations with respect to rigid attachment of the wristpin to other components can also be represented. In the equations of motions solved, all gas pressure, inertia, friction and oil or contact pressure forces are accounted for.

The duration of piston durability tests is often shortened by increasing mechanical and thermal engine loads and loading frequency. Such durability tests are useful for assessing the structural integrity of new piston designs, but test results are generally not indicative of the expected service life. Furthermore, improper test procedures can introduce illegitimate failure modes which are not present in actual service. Two aluminum pistons were analyzed to gain a fundamental understanding of piston response due to accelerated test loads. The influence of engine speed, fuel/air ratio, intake manifold pressure and crankcase oil temperature on piston fatigue life was studied. Guidelines were established to aid in developing a more effective durability test procedure for natural gas engine pistons.

An integrated simulation methodology for the analysis of piston tribology is presented. The methodology is comprised of coupled models of piston secondary dynamics, skirt oil film elastohydrodynamic lubrication and wristpin bearing hydrodynamics, developed earlier by the authors. Models have been further expanded to calculate distributions of cumulative wear load on the skirt and cylinder and to account for details of skirt crankcase end geometry. The skirt elasticity model has also been improved to account for the effects of piston crown and pin boss stiffness in conventional, one-piece pistons. The model predicts piston assembly secondary motions, piston (skirt) friction, skirt and wristpin oil film pressures, transient deformations, skirt-cylinder contact/impact pressures and skirt and cylinder wear loads.

A model for oil consumption due to in-cylinder evaporation of oil in reciprocating engines, has been developed. The model is based on conservation of mass and energy on the surface of the oil film left on the cylinder by a piston ring pack, at the oil/gas interface, and also conservation of energy within the oil film and cylinder/coolant interface. The model is sensitive to in-cylinder conditions and is part of an integrated model of ring pack performance, which provides the geometry of the oil film left by the ring pack on the cylinder. Preliminary simulation results indicate that a relatively small but not insignificant fraction (2-5%) of the total oil consumption may be due to evaporation losses for a heavy duty diesel at the rated condition. The evaporation rate was shown to be sensitive to oil grade and upper cylinder temperature. Much of these losses occur during the non-firing half of the cycle.

A comprehensive diesel engine system model, representing in detail engine heat transfer processes, has been applied to a study of insulated diesel engines. The study involved a broad design analysis matrix covering a range of engine configurations with and without inter-cooling and exhaust heat recovery devices, three operating conditions and seven heat rejection packages. The main findig of this study is that the retained heat conversion efficiency (RHCE), of the in-cylinder heat retained by insulation to piston work, is 35-40 percent; these levels of RHCE are larger than those predicted by previous models. This means that a significant part of the retained heat is converted directly to piston work rather than being merely available in the exhaust stream, from which it would be recoverable with a much lower efficiency.