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Large Eddy Simulation (LES) represents nowadays one of the most promising techniques for the evaluation of the dynamics and evolution of turbulent structures characterizing internal combustion engines (ICE). In the present paper, subdivided into two parts, the capabilities of the open-source CFD code OpenFOAM® v2.3.0 are assessed in order to evaluate its suitability for engine cold flow LES analyses. Firstly, the code dissipative attitude is evaluated through an inviscid vortex convection test to ensure that the levels of numerical dissipation are compatible with LES needs. Quality and completeness estimators for LES simulations are then proposed. In particular the Pope M parameter is used as a LES completeness indicator while the LSR parameter provides useful insights far calibrating the grid density. Other parameters such as the two-grid LESIQk index are also discussed.

In scooter/motorbike engines coherent and stable tumble motion generation is still considered an effective mean in order to both reduce engine emissions and promote higher levels of combustion efficiency. The scientific research also assessed that squish motion is an effective mean for speeding up the combustion in a combustion process already fast. In a previous technical paper the authors demonstrated that for an engine having a high C/D ratio the squish motion is not only not necessary but also detrimental for the stability of the tumble motion itself, because there is a strong interaction between these two motions with the consequent formation of secondary vortices, which in turn penalizes the tumble breakdown and the turbulent kinetic energy production.

Faster combustion and lower cycle-to-cycle variability are mandatory tasks for naturally aspirated engines to reduce emission levels and to increase engine efficiency. The promotion of a stable and coherent tumble structure is considered as one of the best way to promote the in-cylinder turbulence and therefore the combustion velocity. During the compression stroke the tumble vortex is deformed, accelerated and its breakdown in smaller eddies leads to the turbulence enhancement process. The prediction of the final level of turbulence for a particular engine operating point is crucial during the engine design process because it represents a practical comparative means for different engine solutions. The tumble ratio parameter value represents a first step toward the evaluation of the turbulence level at ignition time, but it has an intrinsic limit.

Today, multi-hole Diesel injectors can be mainly characterized by three different nozzle hole shapes: cylindrical, k-hole, and ks-hole. The nozzle hole layout plays a direct influence on the injector internal flow field characteristics and, in particular, on the cavitation and turbulence evolution over the hole length. In turn, the changes on the injector internal flow correlated to the nozzle shape produce immediate effects on the emerging spray. In the present paper, the fluid dynamic performance of three different Diesel nozzle hole shapes are evaluated: cylindrical, k-hole, and ks-hole. The ks-hole geometry was experimentally characterized in order to find out its real internal shape. First, the three nozzle shapes were studied by a fully transient CFD multiphase simulation to understand their differences in the internal flow field evolutions. In detail, the attention was focused on the turbulence and cavitation levels at hole exit.

Metallic open-cell foams have proven to be valuable for many engineering applications. Their success is mainly related to mechanical strength, low density, high specific surface, good thermal exchange, low flow resistance and sound absorption properties. The present work aims to investigate three principal aspects of real foams: the geometrical characterization, the flow regime characterization, the effects of the pore size and the porosity on the pressure drop. The first aspect is very important, since the geometrical properties depend on other parameters, such as porosity, cell/pore size and specific surface. A statistical evaluation of the cell size of a foam sample is necessary to define both its geometrical characteristics and the flow pattern at a given input velocity. To this purpose, a procedure which statistically computes the number of cells and pores with a given size has been implemented in order to obtain the diameter distribution.

In PFI and GDI engines the tumble motion is the most important charge motion for enhancing the in-cylinder turbulence level at ignition time close to the spark plug position. In the open literature different studies were reported on the tumble motion, experimental and not. In the present paper the research activity on the tumble generation at partial load and very partial load conditions was presented. The added value of the analysis was the study of the effect of the throttle valve rotational direction on the tumble motion and the final level of turbulence at the ignition time close to the spark plug location. The focus was to determine if the throttle rotational direction was crucial for the tumble ratio and the turbulence level. The analyzed engine was a PFI 4-valves motorcycle engine. The engine geometry was formed by the intake duct and the cylinder. The CFD code was FIRE AVL code 2013.1.