A correct prediction of the initial stages of the combustion process in SI engines is of great importance to understand how local flow conditions, fuel properties, mixture stratification and ignition affect the in-cylinder pressure development and pollutant formation. However, flame kernel growth is governed by many interacting processes including energy transfer from the electrical circuit to the gas phase, interaction between the plasma channel and the flow field, transition between different combustion regimes and gas expansion at very high temperatures.In this work, the authors intend to present a comprehensive, multi-dimensional model that can be used to predict the initial combustion stages in SI engines. In particular, the spark channel is represented by a set of Lagrangian particles where each one of them acts as a single flame kernel. Each particle is convected by the gas flow and its growth is governed by flame speed and thermal expansion due to the energy transfer from the electrical circuit. From particle positions and size it is then possible to reconstruct the flame surface density distribution, that is then used by the gas phase to compute the fuel reaction rate. A simplified model for the secondary electrical circuit was applied to estimate the amount of energy transferred as function of the circuit properties (equivalent resistance and inductance), discharge energy and time. To compute the flame kernel expansion velocity, the heat conduction equation was solved accounting for real gas properties in the 5000 - 50000 K temperature range. All the effects of the flame kernel growth are grouped into a single source term, that is added to the flame surface density transport equation, solved following the Extended Coherent Flamelet Model (ECFM).The proposed model has been extensively validated with experimental data provided by Herweg et al., illustrated in [1, 2]. A computational mesh reproducing the geometrical details of the optical, pre-chamber SI engine was built, including the electrodes. Initially, cold-flow simulations were carried out to verify the validity of the computed flow-field and turbulent distribution at ignition time. Then, the combustion process was simulated accounting for the effects of different engine speeds, air/fuel ratio, ignition systems and spark-plug position. Validation was performed by comparing computed and experimental evolution of the burned gas volume. Encouraging results were achieved for a wide range of operating conditions.

The increasing need of more and more efficient gearboxes implies the need of predictive models in order to compare, during the design stage, different design solutions. The models provided by literature are mostly experimentally derived and not accurate on real applications. A new trend suggests the adoption of computational fluid dynamics (CFD) for the calculation of the no‐load losses of gear transmissions. In this sense, literature provides some works, but most of them involve only one single phase. In this paper, the real operating condition in which the gears are immersed in an oil lubricant mixture is studied. Adopting an open‐source code, OpenFOAM®, the influence of some operating and geometrical parameters on the churning losses has been investigated. The aims are both to provide data that can be effectively used by engineers in the design practice and to prove, once again, CFD to be an effective approach for this kind of investigations. Copyright © 2014 John Wiley & Sons, Ltd.

Efficiency improvement is one of the main challenges in all fields of design. The reduction of power losses is becoming a great concern also in the design of power transmissions. For this reason it is important to have specific models available in order to quantify the power losses during the design stage. The power losses of a gear transmission can be subdivided into bearing losses, seal losses, meshing losses and hydraulic losses. Although literature provides models for the prediction of losses related to bearings or to gear meshing, for the calculations of the losses generated by the interaction with the lubricant, only few and simplified models are available. For this reason the authors recognize that a general purpose method is required in order to overcome this lack of fit and to improve the capability to predict the efficiency of gearboxes. Being able to compare different design solutions means being able to improve the efficiency, reduce the operating temperature and, consequently, improve the reliability of the system. In this paper, the windage losses generated by a single rotating gear have been studied exploiting different numerical approaches. The results obtained have been compared with measurements showing good agreement.