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Engine knock is one of the most limiting factors for modern Spark-Ignition (SI) engines to achieve high efficiency targets. The stochastic nature of knock in SI units hinders the predictive capability of RANS knock models, which are based on ensemble averaged quantities. To this aim, a knock model grounded in statistics was recently developed in the RANS formalism. The model is able to infer a presumed log-normal distribution of knocking cycles from a single RANS simulation by means of transport equations for variances and turbulence-derived probability density functions (PDFs) for physical quantities. As a main advantage, the model is able to estimate the earliest knock severity experienced when moving the operating condition into the knocking regime.

External gear pumps and motors are robust and low cost positive displacement machines and are widely used in industrial and mobile applications. Nowadays however, optimal global efficiency represents a more crucial aspect to be considered when designing a hydraulic machine. For this reason, it becomes a primary necessity to investigate the phenomena which determine and affect the hydraulic machine total efficiency. In this work, the volumetric efficiency dependence on the operating speed and delivery pressure of external gear pumps is investigated by means of a mathematical model already presented in a previous paper and the results obtained are compared with experimental data. First of all, the mathematical model is briefly presented; then the predicted results are discussed considering the influence of the pump operating conditions.

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.