Refine Your Search



Search Results

Technical Paper

Application of an Integrated CFD Methodology for the Aerodynamic and Thermal Management Design of a Hi-Performance Motorcycle

Though CFD methods have become very popular and widespread tools in the early as well as more advanced automotive design stages, they are still not so common in the motorcycle industry branch. The present work aims at the development of a comprehensive simulation environment, based on the open-source finite volume toolbox OpenFOAM®, for the aerodynamic and thermal fluxes optimization of a full motorcycle-and-rider geometry. The paper is divided in two parts: in the first one, the OpenFOAM® code is evaluated for a cold flow aerodynamic analysis, using a slightly simplified version of the Aprilia RSV4 motorbike geometry; in the second one, a mixed reduced scale-full scale methodology is proposed for the simultaneous assessment of aerodynamic forces and heat transfer performances of the engine cooling system. Results have been compared against other well established commercial CFD packages and, where available, with experimental measurements.
Technical Paper

On the Steady and Unsteady Turbulence Modeling in Ground Vehicle Aerodynamic Design and Optimization

Computational Fluid Dynamics is nowadays largely employed as an effective optimization tool in the automotive industry, especially for what concerns aerodynamic design driven by critical factors such as the engine cooling system optimization and the reduction of drag forces, both limited by continuously changing stylistic constraints. The Ahmed reference model is a generic car-type bluff body with a slant back, which is frequently used as a benchmark test case by industrial as well as academic researchers, in order to investigate the performances of different turbulence modeling approaches. In spite of its relatively simple geometry, the Ahmed model possesses many of the typical aerodynamic features of a modern passenger car - a bluff body with separated boundary layers, recirculating flows and complex three-dimensional wake structures.
Journal Article

Modeling liquid break-up through a kinetic approach

Liquid atomisation is an important technical field for a wide range of engineering and industrial applications, particularly in the field of internal combustion engines. In these engines, in fact, the amount of pollutants at the engine-out interface is directly related to the quality of the combustion process, which is in turn determined by the quality of the air-fuel mixture preparation in Direct Injection (DI) engines. As a consequence numerical-experimental research is crucial to their development. Despite the significant amount of research that has been carried out on DI engines simulation, breakup modelling is still a challenge. In this paper we present a new numerical model for multiphase flows that could be particularly suited for liquid jet and droplet breakup simulation. The model is based on a Lattice Boltzmann (LB) solver coupled to a higher order finite difference treatment of the kinetic forces arising from non-ideal interactions (potential energy).
Technical Paper

Parametric Study of Physical Requirements for Optimization of the EGR-rate and the Spray Formation for Minimum Emissions Production Over a Broad Range of Load/Speed Conditions

The present paper describes a study, which can enable a small displacement (1.3 liter) turbocharged European CR-diesel engine to tolerate an important increase in EGR-level. The analysis is performed by use of a 3D virtual numerical engine model, which isolates the main parameters that must be optimized within the perimeter of the combustion chamber. The paper gives a short introduction to the physical background for NOx and soot-formation as well as a recall of the main issues related to the simulation models used in the virtual engine simulation. The analysis is performed in a 9 points load/speed test matrix. Several EGR-rates are studied as well as the impact of a precise temperature control of the exhaust gas re-introduced in the intake manifold. The paper concludes by an analysis of the cumulated impact on the EGR-level tolerated by the engine after the introduction of the suggested optimization measures.
Technical Paper

Study of the Influence of the Injection System in a Multi-Dimensional Spray Simulation

The introduction of the high-pressure fully electronic-controlled injection systems has opened a number of new possibilities to optimize diesel engine performance and to reduce pollutant emissions. However greater research efforts are required to meet future European emission legislation. The control of the combustion process, which determines to a large extent the amount of pollutant emissions, requires primarily an understanding of its physics and chemistry as well as the capability to modify one or more of the interdependent process parameters in a given direction. Since many parameters have to be considered, a combined experimental-numerical approach is required.
Technical Paper

Optimization by CFD Simulation of Spray Formation Parameters to Adapt Direct Injection High-Pressure Fuel Injectors to High-Speed SI-Engines

The main objective of the paper is to describe the optimization work performed to adjust direct injection (DI)-technology to SI-engines running at high (8000 to 10000 rpm.) and extremely high speeds (more than 18000 rpm). In the first category are located a certain number of small and middle displacement two-stroke series produced engines. In the second category are the typical high power racing engines used for competitions like the formula 1. The first part of the paper describes the particular requirements that an in-cylinder fuelling and mixture preparation will have to fulfill with the extremely short period available for introduction and vaporization of the fuel. The paper continues with a description of the different spray shapes, spray penetration velocities and atomization capabilities, which are optimal for the different combustion chamber architectures.
Technical Paper

Study of the Impact on the Spray Shape Stability and the Combustion Process of Supply Pressure Fluctuations in CR-Diesel Injectors

The paper presents a study of the influence of fuel pressure supply fluctuations on the upstream side of the fuel injector atomizer. The study is performed over a wide range of pressures (70 to 130 Mpa) with two different common-rail (CR) high-pressure fuel injectors. The common atomizer is a VCO-type equipped with conically shaped atomizer bores. With the injector tip (nozzle) mounted in a counter-pressure vessel the pressure fluctuations in the fuel-rail and in the injector body are recorded simultaneously with stroboscopic Schlieren-visualization of the time-resolved spray behavior. It is demonstrated that not only the instantaneous mass flow is affected. As a function of rail-pressure, pulse-width and injection strategy the pressure fluctuations change the spray hard-core structure and its break-up behavior.
Technical Paper

Study of the Impact on the Combustion Process of Injector Nozzle Layout creating Enhanced Secondary Spray Break-up

The paper presents a study of a key-element in the mixture preparation process. A typical common-rail (CR) high-pressure fuel injector was fitted with a prototype injector nozzle with atomizer bores of a particular conical layout. It is demonstrated within certain layout limits, that a considerable enhancement can be obtained for the secondary break-up of the hard-core fluid sprays produced by the nozzle. The impact on the combustion process is examined in terms of pressure and heat release as well as of the engine-out pollutant emission. The results are compared to those of an earlier developed CR high-pressure injector nozzle. The atomization behavior of the prototype nozzle is illustrated through experimental results in terms of engine-out emissions from a 1.3-liter turbo-charged passenger car diesel engine. The detailed spray behavior is visualized on a component test rig by use of specially developed optical visualization techniques.
Technical Paper

Experimental Analysis and CFD Simulation of GDI Sprays

Numerical and experimental analyses of hollow cone sprays generated by pressure-swirl injectors for Direct Injection Spark Ignition (DISI) engines have been performed. Spray characteristics have been measured by a gathering and processing system for spray images, including a CCD camera, a frame grabber and a pulsed sheet obtained by the second harmonic of Nd-YAG laser (wavelength 532 nm, width 12 ns, thickness 100 μm). A detailed spatial and temporal characterization of the emerging spray has been carried out showing interesting peculiarities of the jet for different operative conditions. Some results of a work in progress, aiming to select and to validate proper models for the spray development simulation are, also, discussed. Numerical calculations are based on the KIVA 3V code modified in basic spray sub models. Some important physical phenomena are captured in the computations at the backpressure of 0.1 MPa.
Technical Paper

Direct Injection for Future SI-Engines - Stand Alone Combustion Layout or Integrated Part of Multi-Function Fuel/Air Management Approach?

In the future generation of low consumption SI-engine layouts, it has become necessary to reduce costs as well as the complexity level and, increase the system reliability by the latter. To avoid driving the GDI-system in the critical, very lean stratified operation mode without losing the fuel consumption benefit, a solution is suggested, which combines a fully variable valve control system with a low level, robust GDI combustion layout. The first part of the present paper presents the latest development in the field of high precision multi-hole GDI injector spray nozzles. The basic aspects of mixture preparation with multi-hole gasoline atomizers are highlighted and their spray behavior compared to that of the current swirl atomizer nozzle. The second part of the paper presents primary optimization of a largely homogeneous GDI combustion layout combined with a fully variable valve timing control system including complete cylinder de-activation.
Technical Paper

Flow Characterization of a High Performance S.I. Engine Intake System - Part 2: Numerical Analysis

In this paper a numerical analysis is carried out of the flow characteristics in the intake system of a high performance engine. To this aim, the experimental flow bench results - obtained in tests performed on a Ducati Corse 4 valves racing engine head and presented in the parallel work [1] - are compared with the numerical ones. In [1] an experimental analysis was performed to evaluate the influence, on the flow characteristics in the intake system of a high performance 4 stroke - 4 valve internal combustion engine Notwithstanding the macroscopic meaning of the measured global coefficients Cd (Discharge Coefficient) and Nt (Tumble Number), the comparative analysis of their respective trends allowed some hypotheses to be drawn on the flow development internally to intake system ducts. In order to confirm the conclusions drawn in [1] and to reach a deeper insight in the flow characteristics, numerical simulations were performed.
Technical Paper

Combustion and Spray Simulation of a DI Turbocharged Diesel Engine

The recent innovations on automotive Diesel engines require significant research efforts. The new generation of fully electronically controlled injection systems have opened new ways to reduce emissions and improve the efficiency of the engine. The free mapping of injection law together with the enhanced injection pressures favor, in fact, the optimization of mixture formation. In this field, the 3D simulation is playing a substantial role to support the design of combustion chamber. This paper presents a computational model to simulate the multi-injection process, the mixture formation and the combustion of DI diesel engines with high-pressure injection systems. The main code is a modified version of the KIVA 3V and the modifications presented in this work are a high pressure break up model and a multi component evaporation model. The code has been validated through experimental data on a 4-cylinder, 1910 cc, DI turbocharged Diesel engine (Fiat 1.9 JTD).
Technical Paper

CFD-Aided Design of an Airbox for Race Cars

The design of a “high-performance” airbox for a naturally aspirated internal combustion engine (ICE) of a car racing in prototype sport competitions is described. A computational approach to achieve optimum airbox geometry in terms of fluid dynamical losses reduction and engine volumetric efficiency improvement is proposed. Experiments on race track have been carried out to test the car performances improvement. The numerical calculations have been done using a 3D numerical code. The code solves finite-difference approximation of the fluid dynamic governing equations (continuity, momentum and energy balance). The solution has been performed numerically by an integration both in space and time by means of the Arbitrarian Lagrangian Eulerian (ALE) technique. The numerical simulations have been carried out imposing steady and unsteady boundary conditions.
Technical Paper

Experimental Validation of a GDI Spray Model

A computational model and an experimental analysis have been performed to study the atomisation processes of hollow cone fuel sprays from a high pressure swirl injector for gasoline direct injection (GDI) engines. The objective has been to obtain reliable simulations and better understood structure and evolution of the spray and its interaction with air the flow field. The 3D computations are based on the KIVA 3 code in which basic spray sub models have been modified to simulate break-up phenomena and evaporation process. Spray characteristics have been measured using a system, able to gather and to process spray images, including a CCD camera, a frame grabber and a pulsed sheet obtained by the second harmonic of Nd-YAG laser (wavelength 532 nm, width 12 ns, thickness 80 μm). The readout system has been triggered by a TTL signal synchronized with the start of injection. A digital image processing software has been used to analyse the collected pictures.
Technical Paper

Study of the Benefits and Drawbacks of a Substantial Increase of Rail-Pressure in GDI-Injector Assemblies

In the present paper are examined the consequences of a substantial rise in the injection pressure for Gasoline Direct Injection (GDI) injector assemblies. The paper presents a comparative study of the spray behavior of two different injector nozzle layouts submitted to current 10 Mpa rail-pressure as well as to a 30 Mpa injection pressure. To evaluate the differences in the fundamental physical spray parameters are used several specially developed optical visualization techniques, which enable phase-Doppler, PIV, Laser-sheet and high-speed recordings of dense high pressure fuel sprays. A recently developed injector actuator and the necessary modifications to existing high-pressure pumps to reach a 30 MPa pressure level in the fuel system are presented. The change in basic spray parameters (time-resolved droplet distribution and spray momentum) caused by the rail-pressure rise is examined.
Technical Paper

Study of the Impact of Variations in the Diesel-Nozzle Geometry Parameters on the Layout of Multiple Injection Strategy

In the present paper the impact of three different geometrical layouts of the discharge nozzle of a high-pressure diesel injector designed is examined for a common rail second generation direct injection system. The paper presents a comparative study of the spray behavior of the three different nozzle layouts connected to a 150 MPa rail-pressure when mounted on a 1.6 liter European passenger car engine. To evaluate experimentally the differences in the fundamental physical spray parameters several specially developed optical visualization techniques are used, which enable phase-Doppler, Laser-sheet and high-speed recordings of dense high pressure sprays. The change in basic spray parameters (time-resolved droplet distribution and spray momentum) caused by the nozzle geometry variation is examined. The impact on the in-cylinder penetration and mixing characteristics is studied with a 3D-numerical simulation code NCF-3D.
Technical Paper

Experimental and Computational Study for the Optimization of Race Car Intake Air Flow

The performances increasing of internal combustion engines for race car has driven to develop special systems in order to improve the volumetric efficiency. To this aim, in the last years, a great effort has been done especially in studying geometries for airbox, turbo-compressors, special exhaust systems, etc. In this paper, the project of a “high-performance” airbox for a naturally aspirated internal combustion engine (ICE) of a car racing in prototype sport competitions is described. In order to optimize the airbox geometry under extremely complex operative conditions, the fluid dynamic phenomena inside the airbox have been studied by means of a three dimensional computational code (3D CFD). This approach has allowed to study different airbox geometry and to define the one to be realized and tested on race track. The new airbox geometry, defined in this way, has brought to good results.
Technical Paper

On the Performance of Car Interior Air Filters

In this study, the performances of two filter media, (Cellulose single layer and dual layered wool non wool/cellulose with electrically charged fibre) for automotive cabin air cleaning application, are investigated. Pressure drops of “clean” and dust loaded filter, fractional efficiencies and behaviour of dust loading were measured. The measurements were carried out in a panel filter housing like that specified by the Society of Automotive Engineers SAE J726 Air Cleaner Test Code. Dual-layered filter, as expected, has filtration efficiency and pressure drops very higher than single layer filter. The flow fields inside the test housing were, also, measured using a Pitot tube. The filter in the housing is exposed to non uniform velocity with very high velocities in the center and lower velocities toward the edge. These velocity variations may be expected to affect the performance of the filter, in terms of efficiency, pressure drops and dust holding capacity.
Technical Paper

Numerical and experimental investigation of an impinging gasoline low- pressure spray

Wall film formation by gasoline low-pressure spray and the droplet rebound are important processes to be taken into account in the design of the inlet ducts and in the control optimization. Numerical simulations are nowadays the only tool able to give some information on the evolution of liquid film in the inlet duct or in the combustion chamber of gasoline engines. This paper presents an extensive numerical and experimental study of the behavior of a low- pressure gasoline injector impinging spray. Spray impingement process was analyzed using an experimental setup that is capable to elaborate spray images gathered in different time steps before and after the impact. Calculations were performed using a modified version of the KIVA3V code. New spray, wall film and post-impingement sub-models were introduced in the code.
Technical Paper

Evolution of a high-pressure spray from a swirled gasoline injector

An extensive experimental work has been made in order to analyze the structure of the spray of a large-angle single-hole high-pressure swirl injector for direct-injection spark-ignited (DISI) gasoline engines. Spatial and temporal evolution measurements of the spray have been carried out in an optically accessible vessel. The spray has been lighted by an 80 mm thickness and 12 ns duration pulsed laser sheet, generated by a 532 nm Nd-YAG laser, both along the spray axis and in cross sections perpendicularly to it. The scattered light has been collected at 90° from the laser sheet direction by a digital CCD camera with a frame grabber synchronized to the single-shot injection command and the laser start pulse. A digital image processing system has allowed analyzing the images collected by the CCD camera. It has been possible to visualize the formation and the spatial and temporal evolution of the initial liquid slug (pre-spray) and of the hollow-cone and solid-cone stray structure.