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Ever increasing specific power of diesel engines has put huge demand on effective thermal management of the pistons for the desired reliability and durability. The piston temperature control is commonly achieved by injecting cooling oil into piston galleries, but the design of the cooling system as well as the boundary conditions used in FEA simulations have so far relied mostly on empirical methods. A numerical procedure using 3D computational fluid dynamics (CFD) has therefore been developed to simulate the cooling process and to estimate the cooling efficiency of gallery. The model is able to predict the detailed oil flow and heat transfer in gallery, of different designs and engine applications, under dynamic conditions. The resulted spatially resolved heat transfer coefficient from the CFD model, with better accuracy, enables improved prediction of piston temperature in finite element analysis (FEA).

Standard bonded transmission piston design specifies the use of low carbon steel for the piston carrier material. High strength low alloy (HSLA) steel is proposed for applications where load and packaging requirements dictate. The impact of carrier material selection on piston design and manufacturing needs to be comprehensively evaluated in these cases. This paper will discuss considerations for using HSLA steel and make recommendations for its application to bonded transmission pistons.

This paper introduces a new hypereutectic aluminum alloy for piston casting, an improved casting process and a new re-melting procedure. The resulting microstructures improve the fatigue performance of the piston combustion bowl region exposed to severe cyclic thermal and mechanical loading in modern diesel engine applications. It is shown how composition and material properties of the new alloy increase the material's fundamental properties, compared to an existing hypereutectic alloy. The new casting process minimizes the occurrence of fine oxide inclusions which helps to exploit the fundamental material strength. Finally the paper describes the combustion bowl re-melting process and gives engine validation results to illustrate its considerable influence on premature fatigue failure.

Bore distortion was measured in a 2.0 liter in-line 4-cylinder gasoline engine, chosen because its siamesed bore design was expected to incur high bore distortion. The method adopted was to install 10 Micro-Epsilon eddy-current transducers in an invar carrier attached to the under crown of the piston. The transducers emerged through apertures in the piston at second ring level where they were in close proximity to the bore surface. A 2-beam linkage system was used to carry miniature co-axial cables to the engine exterior. Measurements were recorded at various speeds and loads up to 6000 rev/min. Maximum bore distortion was 86 microns, arising from clamping loads, thermal effects and combustion pressure. The head bolts spaced around the bore gave rise to fourth order distortion, but the dominant influence was thermal loading which induced second order distortion, attributed directly to the siamesed bore design. The combustion pressure proved to have the least influence.

The objective was to rank piston friction and noise for three piston architectures at three cold clearance conditions. Piston secondary motion was measured using four gap sensors mounted on each piston skirt to better understand the friction and noise results. One noticeable difference in friction performance from conventional designs was as engine speed increased the friction force during the expansion stroke decreased. This was accompanied by relatively small increases in friction force during the other strokes so Friction Mean Effective Pressure (FMEP) for the whole cycle was reduced. Taguchi's Design of Experiment method was used to analyze the variances in friction and noise.

Due to increasing economic and environmental performance requirements of internal combustion engines, piston manufacturers now focus more on lower friction designs. One factor strongly influencing the friction behavior of pistons is the dynamic interaction between lubricating oil, cylinder bore and piston. Therefore, the dynamic effect of the oil film in the gap between the liner and piston has been studied, using a single cylinder engine equipped with a sapphire window. This single cylinder engine was also equipped with a floating liner, enabling real-time friction measurement, and directly linking the oil film behavior to friction performance of pistons.

This paper deals with the friction performance results for various new concept piston skirt profiles. The program was conducted under the assumption that friction performance varies by the total amount of oil available at each crank angle in each stroke and the instantaneous distribution of the oil film over the piston skirt area. In previous papers [1,2] it was that lower friction designs would be expected to show higher skirt slap noise. This paper discusses the correlation between friction and skirt slap for each new concept profile design. Finally, this paper explains the friction reduction mechanism for the test samples for each stroke of the engine cycle by observing the skirt movement and oil lubrication pattern using a visualization engine.

An analytical method is presented in this paper for simulating piston secondary dynamics and piston-bore contact for an asymmetric half piston model including elastohydrodynamic (EHD) lubrication at the bore-skirt interface. A piston EHD analysis is used based on a finite-difference formulation. The oil film is discretized using a two-dimensional mesh. For improved computational efficiency without loss of accuracy, the Reynolds’ equation is solved using a perturbation approach which utilizes an “influence zone” concept, and a successive over-relaxation solver. The analysis includes several important physical attributes such as bore distortion effects due to mechanical and thermal deformation, inertia loading and piston barrelity and ovality. A Newmark-Beta time integration scheme combined with a Newton-Raphson linearization, calculates the piston secondary motion.