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The materials commonly employed in the automotive industry are various and depend on the specific application field. For what concern the internal combustion engines the choice is guided by the thermomechanical performance required, technological constraints and production costs. Actually, for high-performance engines, steel and aluminium are the most common materials selected for the piston and the cylinder liner manufacturing. This study analyses the effect of possible material choice on the interaction between piston and cylinder liner, via Finite Element analyses. A motorcycle engine is investigated considering two possible pistons: one (standard) made of aluminium and one made of steel. Similarly, two possible cylinder liners are considered, the original one made of aluminium and a different version made of steel obtained by simply thinning the aluminium component in order to obtain two structurally equivalent components.

Bearings represent one of the main causes of friction losses in internal combustion engines, and their lubrication performance has a crucial influence on the operating condition of the engine. In particular, the conrod small-end bearing is one of the most critical engine parts from a tribological point of view since limited contact surfaces have to support high inertial and combustion forces. In this contribution an analysis is performed of the tribological behavior of the lubricated contact between the piston pin and the conrod small-end of a high performance motorbike engine. A mass-conserving algorithm is employed to solve the Reynolds equation based on a complementarity formulation of the cavitation problem. The analysis of the asperity contact problem is addressed in detail. A comparison between two different approaches is presented, the former based on the standard Greenwood/Tripp theory and the latter based on a complementarity formulation of the asperity contact problem.

Modern high performance engines are usually characterized by high power densities, which lead to high mechanical and thermal loadings acting on engine components. In this scenario, aluminum may not represent the best choice for piston manufacturing and steel may be considered as a valid alternative. In this article, a methodology involving optimization techniques is presented for the design of an internal combustion engine piston. In particular, a design strategy is preliminary investigated aiming at replacing the standard aluminum piston, usually manufactured by forging or casting, with an alternative one made of steel and manufactured via an Additive Manufacturing process. Three different loading conditions are employed for the topology optimizations setup. Optimization results are then interpreted and the various structural features of the steel piston are designed starting from the density distribution contour plots.

A 2200 cc engine head for marine applications has been analysed and optimized by means of decoupled CFD and FEM simulations in order to assess the fatigue strength of the component. The fluid distribution within the cooling jacket was extensively analysed and improved in previous works, in order to enhance the performance of the coolant galleries. A simplified methodology was then proposed in order to estimate the thermo-mechanical behaviour of the head under actual engine operation [1, 2]. As a consequence of the many complex phenomena involved, an improved approach is presented in this paper, capable of a better characterization of the fatigue strength of the engine head under both high-cycle and low-cycle fatigue loadings. The improved methodology is once again based on a decoupled CFD and FEM analysis, with relevant improvements added to both simulation realms.

In this paper a detailed analysis focused on lumped parameters numerical modeling of high speed direct injected internal combustion engine cooling systems is presented and discussed. More in details, the cooling systems here studied are characterized by extreme performance, both in terms of circulating flow rates and thermal loads. First of all, a comprehensive description of the simulation environment properly tailored for cooling systems modeling is introduced and all its geometric, fluid-dynamic and thermodynamic characteristics are described in depth. Then, the model has been validated through an exhaustive numerical vs. experimental comparison, involving both cold and hot engine operation, for a wide range of rotational speeds. The general good accordance obtained between calculated and measured results clearly demonstrate the reliability of the numerical model.

For the investigation of the tribological behavior of lubricated contacts, the choice and the calibration of the adopted asperity contact model is fundamental, in order to properly mimic the mixed lubrication conditions. The Greenwood/Tripp model is extensively adopted by the commercial software commonly employed to simulate lubricated contacts. This model, based on a statistic evaluation of the number of asperities in contact and on the Hertzian contact theory, has the advantage of introducing a simple relationship between oil film thickness and asperity contact pressure, considerably reducing the simulation time. However, in order to calibrate the model, some non-standard roughness parameters are required, that are not available from commercial roughness measuring equipment. Standard values, based on some limited experiences, are typically used, and a limited literature can be found focusing on how to evaluate them, thus reducing the predictivity of the model.

The paper presents a combined experimental and numerical activity carried out to improve the accuracy of conjugate heat transfer CFD simulations of a high-performance S.I. motorbike engine water cooling jacket. The computational domain covers both the coolant jacket and the surrounding metal components (head, block, gasket, valves, valve seats, valve guides, cylinder liner, spark plug). In view of the complexity of the modeled geometry, particular care is required in order to find a tradeoff between the accuracy and the cost-effectiveness of the numerical procedure. The CFD-CHT simulation of water cooling jackets involves many complex physical phenomena: in order to setup a robust numerical procedure, the contribution of some relevant CFD parameters and sub-models was discussed by the authors in previous publications and is referred to [1, 2, 3, 4].

This paper reports an analysis of the lubrication mechanism and the dynamic behaviour of axial piston pumps and motors slipper bearings. A numerical procedure is used to solve the Reynolds equation, written here with respect to the slipper-swash plate gap, whose height is considered variable in a two dimensional field and with time. The contributions of forces and moments acting on the slipper are illustrated and discussed, then the numerical method is presented to solve the Reynolds equation. Taking into consideration the slipper surface that is facing the swash plate, different geometry profiles are considered and the subsequent dynamic behaviour of the slipper is investigated; in particular, it is shown that a flat profile cannot always guarantee the bearing capability of the slipper and the lubrication in the gap is compromised for some critical operating conditions.