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The paper compares two different design concepts for a range extender engine rated at 30 kW at 4500 rpm. The first project is a conventional 4-Stroke SI engine, 2-cylinder, 2-valve, equipped with port fuel injection. The second is a new type of 2-Stroke loop scavenged SI engine, featuring a direct gasoline injection and a patented rotary valve for enhancing the induction and scavenging processes. Both power units have been virtually designed with the help of CFD simulation. Moreover, for the 2-Stroke engine, a prototype has been also built and tested at the dynamometer bench, allowing the authors to make a reliable theoretical comparison with the well assessed 4-Stroke unit.

This paper proposes the CFD simulation of the oil splashing within the discs’ chamber of a novel concept for axle dry braking system in off-highway vehicles. The system completely removes the lubricating oil from the discs’ chamber during the not-engaged configuration of the friction plates and it quickly restore it at the beginning of the braking stage when the discs’ cooling becomes crucial, thus ensuring a significant reduction of the power losses. The CFD analysis of the real component is performed to predict the efficiency of the system in terms of both the time needed to replenish the discs’ chamber when brake is actuated, and the hydraulic torque exerted by the splashing of the oil. The entire three-dimensional geometry of the domain is accurately discretized, and the multi-phase flow nature is addressed by means of the volume of fluid approach.

Knock is one of the main limitations on Spark-Ignited (SI) Internal Combustion Engine (ICE) performance and efficiency and so has been the object of study for over one hundred years. Great strides have been made in terms of understanding in that time, but certain rather elementary practical problems remain. One of these is how to interpret if a running engine is knocking and how likely this is to result in damage. Knocking in a development environment is typically quantified based on numerical descriptions of the high frequency content of a cylinder pressure signal. Certain key frequencies are observed, which Draper [1] explained with fundamental acoustic theory back in 1935. Since then, a number of approaches of varying complexity have been employed to correlate what is happening within the chamber with what is measured by a pressure transducer.

The increasing limitations in engine emissions and fuel consumption have led researchers to the need to accurately predict combustion and related events in gasoline engines. In particular, knock is one of the most limiting factors for modern SI units, severely hindering thermal efficiency improvements. Modern CFD simulations are becoming an affordable instrument to support experimental practice from the early design to the detailed calibration stage. To this aim, combustion and knock models in RANS formalism provide good time-to-solution trade-off allowing to simulate mean flame front propagation and flame brush geometry, as well as “ensemble average” knock tendency in end-gases. Still, the level of confidence in the use of CFD tools strongly relies on the possibility to validate models and methodologies against experimental measurements.

With the aim of identifying technical solutions to lower the particulate matter emissions, the engine research community made a consistent effort to investigate the root causes leading to soot formation. Nowadays, the computational power increase allows the use of advanced soot emissions models in 3D-CFD turbulent reacting flows simulations. However, the adaptation of soot models originally developed for Diesel applications to gasoline direct injection engines is still an ongoing process. A limited number of studies in literature attempted to model soot produced by gasoline direct injection engines, obtaining a qualitative agreement with the experiments. To the authors’ best knowledge, none of the previous studies provided a methodology to quantitatively match particulate matter, particulate number and particle size distribution function measured at the exhaust without a case-by-case soot model tuning.

CFD simulations of reacting flows are fundamental investigation tools used to predict combustion behaviour and pollutants formation in modern internal combustion engines. Focusing on spark-ignited units, most of the flamelet-based combustion models adopted in current simulations use the fuel/air/residual laminar flame propagation speed as a background to predict the turbulent flame speed. This, in turn, is a fundamental requirement to model the effective burn rate. A consolidated approach in engine combustion simulations relies on the adoption of empirical correlations for laminar flame speed, which are derived from fitting of combustion experiments. However, these last are conducted at pressure and temperature ranges largely different from those encountered in engines: for this reason, correlation extrapolation at engine conditions is inevitably accepted. As a consequence, relevant differences between proposed correlations emerge even for the same fuel and conditions.

This work reports a CFD study on a 2-stroke (2-S) opposed piston high speed direct injection (HSDI) Diesel engine. The engine main features (bore, stroke, port timings, et cetera) are defined in a previous stage of the project, while the current analysis is focused on the assembly made up of scavenge ports, manifold and cylinder. The first step of the study consists in the construction of a parametric mesh on a simplified geometry. Two geometric parameters and three different operating conditions are considered. A CFD-3D simulation by using a customized version of the KIVA-4 code is performed on a set of 243 different cases, sweeping all the most interesting combinations of geometric parameters and operating conditions. The post-processing of this huge amount of data allow us to define the most effective geometric configuration, named baseline.

The recent interest in alternative non-fossil fuels has led researchers to evaluate several alcohol-based formulations. However, one of the main requirements for innovative fuels is to be compatible with existing units’ hardware, so that full replacement or smart flexible-fuel strategies can be smoothly adopted. n-Butanol is considered as a promising candidate to replace commercial gasoline, given its ease of production from bio-mass and its main physical and chemical properties similar to those of Gasoline. The compared behavior of n-butanol and gasoline was analyzed in an optically-accessible DISI engine in a previous paper [1]. CFD simulations explained the main outcomes of the experimental campaign in terms of combustion behavior for two operating conditions. In particular, the first-order role of the slower evaporation rate of n-butanol compared to gasoline was highlighted when the two fuels were operated under the same injection phasing.

Large-eddy simulation (LES) applications for internal combustion engine (ICE) flows are constantly growing due to the increase of computing resources and the availability of suitable CFD codes, methods and practices. The LES superior capability for modeling spatial and temporal evolution of turbulent flow structures with reference to RANS makes it a promising tool for describing, and possibly motivating, ICE cycle-to-cycle variability (CCV) and cycle-resolved events such as knock and misfire. Despite the growing interest towards LES in the academic community, applications to ICE flows are still limited. One of the reasons for such discrepancy is the uncertainty in the estimation of the LES computational cost. This in turn is mainly dependent on grid density, the CFD domain extent, the time step size and the overall number of cycles to be run. Grid density is directly linked to the possibility of reducing modeling assumptions for sub-grid scales.

Polymer Electrolyte Membrane Fuel Cell (PEMFC) are among the most promising technologies as energy conversion devices for the transportation sector due to their potential to eliminate, or greatly reduce, the production of greenhouse gases. One of the current issues with this type of technology is thermal management, which is a key aspect in the design and optimization of PEMFC, whose main aim is an effective and balanced heat removal, thus avoiding thermal gradients leading to a cell lifetime reduction as well as a decrease in the output performance. In addition, a uniform temperature distribution contributes to the achievement of a uniform current density, as it affects the rate of the electrochemical reaction. This is made even more challenging due to the low operating temperature (80°C), reducing the temperature difference for heat dissipation, and leaving a critical role to the design and optimization of the cooling circuit design.

Hydrogen-fueled Proton Exchange Membrane Fuel Cells (PEMFC) are considered one of the most promising technologies for a fully sustainable power generation in the transportation sector, thanks to the direct conversion of chemical-electrical energy, the absence of harmful emissions, the optimal power density, and the allowable long-distance driving range. A current technological issue preventing their large-scale industrialization is the thermal management of PEMFC stacks, due to the absence of the heat removal action operated by exhaust gases in internal combustion engines, the low-temperature generated heat and the limited exchange areas in mobile applications. A relevant role in heat dissipation is played by bipolar plates, being the components with the largest volume occupation and greatly contributing to the PEMFC weight and cost.

The paper investigates the lubrication flow within multi plate wet-clutches for hydro-mechanical variable transmissions in order to optimize the oil distribution and to reduce the thermo-mechanical stresses on the plates. Since experimental measurements are very difficult to carry out on a real system, CFD numerical tools are used for predicting the flow distribution in a real geometry under actual operating conditions. A modular approach is adopted for the domain subdivision in order to represent accurately the three dimensional geometrical features, while the volume of fluid approach is used to model the multi-phase flow that characterizes the component. Poor lubrication is predicted where high thermal stresses were observed during tests. Furthermore, the numerical modeling is validated against measurements carried out on an ad-hoc designed test rig, which adopts transparent PMMA and 3D-printed inserts for the flow investigation.

Oxygen enriched air (EA) is a well known industrial mixture in which the content of oxygen is higher respect the atmospheric one, in the range 22-35%. Oxygen EA can be obtained by desorption from water, taking advantage of the higher oxygen solubility in water compared to the nitrogen one, since the Henry constants of this two gases are different. The production of EA by this new approach was already studied by experimental runs and theoretical considerations. New results using salt water are reported. EA promoted combustion is considered as one of the most interesting technologies to improve the performance in diesel engines and to simultaneously control and reduce pollution. This paper explores, by means of 3-dimensional computational fluid dynamics simulations, the effects of EA on the performance and exhaust emissions of a high-speed direct-injection diesel engine.

The accurate representation of Internal Combustion Engine (ICE) flows via CFD is an extremely complex task: it strongly depends on a combination of highly impacting factors, such as grid resolution (both local and global), choice of the turbulence model, numeric schemes and mesh motion technique. A well-founded choice must be made in order to avoid excessive computational cost and numerical difficulties arising from the combination of fine computational grids, high-order numeric schemes and geometrical complexity typical of ICEs. The paper focuses on the comparison between different mesh motion technologies, namely layer addition and removal, morphing/remapping and overset grids. Different grid strategies for a chosen mesh motion technology are also discussed. The performance of each mesh technology and grid strategy is evaluated in terms of accuracy and computational efficiency (stability, scalability, robustness).

The paper reports a wide numerical analysis of the well-known “Darmstadt engine” operated under motored condition. The engine, which features multiple optical accesses and is representative of currently made four-valve pentroof GDI production engines, is simulated using computational grids of increasing density and two widely adopted approaches to model turbulence, Reynolds Averaged Navier Stokes (RANS) and Large Eddy Simulation (LES). In the first part of the paper, attention is focused on the increase of grid density within the RANS modelling framework: both bulk-flow grid density and near-wall grid density are varied in order to analyse potentials and limitations of the different grid strategies and evaluate the trade-off between accuracy and computational cost.

The basic requirements for range extender engines are low cost, compact dimensions, high specific power, good efficiency, low pollutant emission levels, excellent NVH behavior. For a power rate lower than 30 kW, it is very difficult to find an off-the-shelf engine meeting all the requirements listed above, so that a new generation of dedicated engines is under development. Following a preliminary theoretical work presented in 2012 [1], the current paper reviews the design process and the first experimental tests carried out on a novel 2-stroke GDI single-cylinder engine, rated at 30 kW at 4500 rpm, featuring a patented induction valve and a piston pump for scavenging. A prototype has been designed with the support of CFD simulations, then built and tested at the BRC laboratories, in Cherasco (Italy).

After-treatment sensors are used in the ECU feedback control to calibrate the engine operating parameters. Due to their contact with exhaust gases, especially NOx sensors are prone to soot deposition with a consequent decay of their performance. Several phenomena occur at the same time leading to sensor contamination: thermophoresis, unburnt hydrocarbons condensation and eddy diffusion of submicron particles. Conversely, soot combustion and shear forces may act in reducing soot deposition. This study proposes a predictive 3D-CFD model for the analysis of the development of soot deposition layer on the sensor surfaces. Alongside with the implementation of deposit and removal mechanisms, the effects on both thermal properties and shape of the surfaces are taken in account. The latter leads to obtain a more accurate and complete modelling of the phenomenon influencing the sensor overall performance.