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Aerodynamic had played a primary role in high performance car since the late 1960s, when introduction of the first inverted wings appeared in some formulas. Race car aerodynamic optimisation is one of the most important reason behind the car performance. Moreover, for high performance car using naturally aspired engine, car aerodynamic has a strong influence also on engine performance by its influence on the engine airbox. To improve engine performance, a detailed fluid dynamic analysis of the car/airbox interaction is highly recommended. To design an airbox geometry, a wide range of aspects must be considered because its geometry influences both car chassis design and whole car aerodynamic efficiency. To study the unsteady fluid dynamic phenomena inside an airbox, numerical approach could be considered as the best way to reach a complete integration between chassis, car aerodynamic design, and airbox design.

The increasing of the overall engine performance requires the investigation of the unsteady engine phenomena affecting intake air flow and the air-fuel mixing process. The “standard” RANS methodology often doesn't allow one to achieve a qualitative and quantitative accurate prediction of these phenomena. The aim of this paper is to show the potential and the limits of LES numerical technique in the simulation of actual IC engine flows and to assess the influence of some basic parameters on the LES simulation results. The paper introduces the use of a merit parameter suggested by Pope for evaluating the quality of the LES solution. The CFD code used is Fluent v6.2 and two basic test cases have been simulated. The first one is the flow over a backward facing step in order to perform a preliminary parametric numerical analysis. A one-equation dynamic subgrid-scales turbulence model is used.

The optimization of the air-fuel mixture formation plays a very important role in order to reduce the total amount of emissions from an SI engine. To comply with the EURO5 emission restrictions is necessary to understand the influence of injection timing (with respect to engine load) and injector geometry on the air-fuel dynamic interaction. The aim of this paper is to define a CFD methodology for the simulation of a PFI engine. The goals of this analysis are the evaluation of the injector geometry and injection timing influences on the air-fuel mixture preparation and so on the equivalence ratio distribution inside the combustion chamber. Preliminary assessments of the wall-film and droplet-wall interaction sub models have been carried out in order to validate the methodology [1].

The efficiency of engine operations, i.e. cold start, transient response and operating at idle, depends on the capability of the injection fuel system to promote a homogeneous mixture formation through an efficient interaction with engine fluid dynamics and geometry. The paper presents the development and the application of a methodology for running a CFD PFI engine simulation. A preliminary assessment of the wall-film and droplet-wall interaction sub models has been carried out in order to validate the methodology. Then a three-step numerical procedure has been adopted. The first two steps are aimed to properly initialize the secondary breakup model depending on the type of injector installed on board in order to achieve accurate predictions of spray characteristics.

A very stringent problem in most of European cities is the individual mobility. This problem is mainly caused by traffic jam and arising from this are two particularly interesting environmental issues: pollution and noise [1]. Use of two wheeler vehicles does not represent the final solution to these problems, nevertheless they can supply a useful aid to ease them. Recently, two stroke engines are being replaced with four stroke engines. For small capacity engines this means a true reduction in exhaust emissions, especially unburned hydrocarbons (HC), but, on the other hand it involves a performance reduction, particularly for sudden accelerations, which constitute an essential requirement for these vehicles [2, 3, 4, 5]. Hybridisation can help to fill the gap between two stroke engines and cleaner, but less performing four stroke engines [6]. At the same time, it can help to lower fuel consumption, by means of a reduction in the revolution speed [2, 5].

An ignition model based on Lagrangian approach was set-up. A lump model for the electrical circuit of the spark plug is used to compute breakdown and glow energy. At the end of shock wave and very first plasma expansion, a spherical kernel is deposited inside the gas flow at spark plug location. A simple model allows one to compute initial flame kernel radius and temperature based on physical mixture properties and spark plug characteristics. The sphere surface of the kernel is discretized by triangular elements which move radially according to a lagrangian approach. Expansion velocity is computed accounting for both heat conduction effect at the highest temperatures and thermodynamic energy balance at relatively lower temperatures. Turbulence effects and thermodynamic properties of the air-fuel mixture are accounted for. Restrikes are possible depending on gas flow velocity and mixture quality at spark location.

The increasing of the overall engine performance requires the investigation of the unsteady engine phenomena affecting intake air flow and the air-fuel mixing process. The “standard” RANS methodology often doesn't allow one to achieve a qualitative and quantitative accurate prediction of these phenomena. The aim of this paper is to show the potential and the limits of LES numerical technique in the simulation of actual IC engine non reactive flows in fixed grids. The paper introduces the use of a merit parameter suggested by Pope for evaluating the quality of the LES turbulence resolution [14]. A basic engine steady flow bench case has been simulated. The CFD code used is Fluent v6.2. The numerical results of a previous LES basic numerical analysis were used for setting up calculations. Large Eddy Simulations using the dynamic one-equation model and a simulation with the WALE sgs model [25] have been performed.

This paper deals with the assessment of the use of LES simulation technique on a real airbox geometry designed for a high-performance engine. Large Eddy Simulation is a promising technique to yield a CFD tool able to predict flow unsteadiness: in LES modeling only a small part of the energy spectrum is modeled while the large scales of motion (correlated with the energy transport phenomena) are directly resolved. Given this observation, LES model becomes a very attractive tool for the fluid dynamic analysis of components characterized by a strong dynamic flow behavior like an airbox geometry. The airbox simulations were performed by Fluent v6.3 CFD code and the Wall Adaptive Local Eddy-Viscosity (WALE) sub-grid (sgs) stress model was used. A bounded second order central differencing scheme (BCD) was adopted and a discussion of the kinetic energy conservation attitude of this scheme was performed.

This paper deals with a CFD three-dimensional multiphase simulation of rotary vane pump. The paper presents a suitable methodology for the investigation of the cavitation effects and/or incondensable gases. All the 3D simulations were performed by using Fluent v12 (Beta version). A moving mesh methodology was defined to reproduce the change-in-time shape of the internal pump volumes. In particular, the pump analysis was focused on the generation, and evolution of the cavitation phenomena inside the machine to identify the locations where this phenomena could occur. Moreover, the influence of incondensable gas dissolved inside the operator fluid on both pump performance and cavitation evolution was evaluated. Significant results were obtained about the analysis of incondensable gas influence on the cavitation evolution showing that, today, CFD analysis can provide detailed information on such harmful phenomena which can not be achieved by experiments.

The preparation of the air-fuel mixture represents one of the most critical tasks in the definition of a clean and efficient SI engine. Therefore it becomes necessary to consolidate the numerical methods which are able to describe such a complex physical process. Within this context, the authors developed a CFD methodology into an open-source code to investigate the air-fuel mixture formation process in PFI engines. Attention is focused on moving mesh algorithms, Lagrangian spray modeling and spray-wall interaction modeling. Since moving grids are involved and the mesh quality during motion strongly influences the computed in-cylinder flow-field, a FEM-based automatic mesh motion solver combined with topological changes was adopted to preserve the grid quality in presence of high boundary deformations like the interaction between the piston bowl and the valves during the valve-overlap period.

Upcoming Euro 4 and Euro 5 emission standards are increasing efforts on injection system developments in order to improve mixture quality and combustion efficiency. The target features of advanced injection systems are related to their capability of operating multiple injection with a precise control of the amount of injected fuel, low cycle-by-cycle variability and life drift, within flexible strategies. In order to accomplish this task, injector performance must be optimised by acting on: optimisation of electronic, driving circuit, detailed investigation of different nozzle hole diameter configurations, assessment of the influence of manufacturing errors on hole diameter and inlet rounding on injector performance. The paper will focus on the use of an integrated lump-1D/3D methodology for the design of advanced new fast solenoid Common Rail (C.R.) injector for high speed diesel engines. A lump-model built up in AMESim® environment was used to address the injector design.

The introduction of high-pressure injection systems in D.I. diesel engines has highlighted already known drawbacks of in-cylinder turbulence modeling. In particular, the well known equilibrium hypothesis is far from being valid even during the compression stroke and moreover during the spray injection and combustion processes when turbulence energy transfer between scales occurs under non-equilibrium conditions. The present paper focuses on modeling in-cylinder engine turbulent flows. Turbulence is accounted for by using the RNG k-ε model which is based on equilibrium turbulence assumptions. By using a modified version of the Kiva-3 code, different mathematically based corrections to the computed macro length scale are proposed in order to account for non-equilibrium effects. These new approaches are applied to a simulation of a recent generation HSDI Diesel engine at both full load and partial load conditions representative of the emission EUDC cycle.

A second generation of Common-Rail injection systems is coming into production making feasible multiple injection strategies. This paper aims to assess the capability of multiple injection in reducing NOx and soot emissions of HSDI Diesel engines. The analysis has been carried out at a characteristic point of the EUDC emission test cycle by using a customized version of the CFD code Kiva3, with updated sub-models developed by University of Bologna and University of Wisconsin. In particular, a recent modification has been introduced in the fuel conversion rate calculation in order to account for turbulence non-equilibrium effects. Different multiple injection profiles and combustion chamber configurations have been simulated and their effects on mixture formation, heat release rate and NOx and soot formation have been analyzed. The main target was to comply with emission standards without significant loss in engine performance.

The paper is focused on the influence of the eddy viscosity turbulence models (EVM) in CFD three-dimensional simulations of steady turbulent engine intake flows in order to assess their reliability in predicting the discharge coefficient. Results have been analysed by means of the comparison with experimental measurements at the steady flow bench. High Reynolds linear and non linear and RNG k-ɛ models have been used for simulation, revealing the strong influence of both the constitutive relation and the ɛ-equation formulation on the obtained results, while limits in the applicability of more sophisticated near-wall approaches are briefly discussed in the paper. Due to the extreme complexity of typical ICE flows and geometries, the analysis of the behaviour of EVM turbulence models has been subsequently applied to a test-case available in literature, i.e. a high-Reynolds compressible flow over a inclined backward facing step (BFS).

0 In this work we illustrate a data acquisition system realization and set up for the experimental description of an air cooling system for a four stroke, one - cylinder engine used on scooters. The high importance of the power absorbed by cooling system at medium and high rotational speeds is the first reason of this investigation, our target is to point out possible increasing in the forced ventilation cooling system performances. First of all, in order to foresee the magnitude order of the measured variables, we developed a theoretical one-dimensional description of the centrifugal blower, with this approach we can forecast, even if in an approximated way, the measured variables magnitude order. Obviously, in order to realize the blower and flow experimental characterization, it was necessary the choice of the right test rig.

The new European legislation on two-wheeler pollutant emissions has forced two stroke engine manufacturers to study the direct fuel injection (DI) technology. The Piaggio “ET2 Injection” was the first DI engine in production, using the FAST system (Fully Atomized Stratified Turbulence) applied on a 50 cm3 engine. Within the framework of the DOLCE project (Development Of innovative Low pollutant, noise and fuel Consumption two stroke spark ignition Engines for future vehicles for individual urban mobility) coordinated by Piaggio and supported by the European Commission, a 125 cm3 direct injection 2-stroke engine was developed. This paper presents the engine-related part of this work, which was concluded in March 2000. The engine is equipped with the FAST system and the fuel metering is performed by means of a low-pressure electronic fuel injection system integrated in an Engine Management System (EMS) specially developed for this type of application.

The first part of the paper gives an overview of the environmental conditions with which a future two stroke engine must comply. The reasons for which a direct gasoline injection into the combustion chamber offers one of the most promising solutions are explained. In order to understand the potential of different GDI-layouts to produce very lean stratified combustion behavior two different approaches are studied in detail. The latest version of the fuel/air mixture injection used by the F. A. S. T. engine is confronted with a basically liquid high-pressure layout, similar to the design used in automotive four-stroke passenger car engines. A description is given of the basic fluid dynamics of the 50 cc engine used for the study as well as of the experimental and numerical tools applied. The paper concludes with a detailed presentation of the obtained results as well as of the arguments retained to produce the final rating.

The aim of this work is to set up a methodology for simulating Common Rail high-pressure injectors based on coupling a lump-model with CFD two-phase multi-dimensional computations. The unit simulated is the Bosch injector. The injector lump-model resulted in the definition of the three sub-models for hydraulics, mechanics and electro-magnetics. The second-order differential governing equations have been solved in Matlab/Simulink environment and are properly coupled together with the one-dimensional partial differential equations that describe the unsteady pipe flow. A detailed library of thermo-mechanical properties for ISO-4113 oil and diesel fuel is included. Cavitation effects on discharge coefficient in the main orifices were accounted for by using results from CFD steady two-phase flow simulations. The evaluation of the model capability was assessed by using detailed experiments carried out at different practical injector operating conditions.

This paper presents a methodology for the 3D CFD simulation of the intake and compression processes of four stroke internal combustion engines.The main feature of this approach is to provide very accurate initial conditions by means of a cost-effective initialization step. Calculations are applied to a low stroke-to-bore SI engine, operated at full load and maximum engine speed. It is demonstrated that initial conditions for this kind of engines have an important influence on flow field development, particularly in terms of mean velocities close to the firing TDC. Simulation results are used to discuss the choice of a set of parameters for the flow field characterization of low stroke-to-bore engines, as well as to provide an insight into the flow patterns during the overlapping period.

The paper is focused on the influence of the eddy viscosity turbulence models (EVM) in CFD three-dimensional simulations of steady turbulent engine intake flows in order to assess their reliability in predicting the discharge coefficient. Results have been analyzed by means of the comparison with experimental measurements at the steady flow bench. High Reynolds linear and non-linear and RNG k-ε models have been used for simulation, revealing the strong influence of both the constitutive relation and the ε-equation formulation on the obtained results, while limits in the applicability of more sophisticated near-wall approaches are briefly discussed in the paper. Due to the extreme complexity of typical ICE flows and geometries, the analysis of the behavior of EVM turbulence models has been subsequently applied to a test-case available in literature, i.e. a high-Reynolds compressible flow over a inclined backward facing step (BFS).