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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).

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.

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.

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.

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.

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.

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.

The first part of the paper gives an overview of the current results obtained with the first-generation of GDI-powered vehicles launched on the European market. In view of the rather limited success in fuel consumption gain the second-generation of very lean stratified layouts has begun, but this process requires the development and application of new high-level analysis tools. A possible high performance approach is the multi-purpose use of 3-D numerical simulation both in the development and the engine control strategy calibration phases. The development of a small 1.6 liter lean stratified engine project was chosen to demonstrate the dual application capability of the NCF-3D simulation tool. The paper continues with a description of the engine application frame, the basic features of the NCF-3D simulation tool and the latest enhancements made to combustion and fuel composition models within the software frame.

The first part of the paper outlines the main potential advantages of the direct fuel injection concept and describes the overall layout of a system in which the keystones are a piston rotary fuel delivery pump with integrated pressure regulation and electromechanical fast responding fuel injectors. Three different nozzle designs are discussed, a divergent pintle solid cone, a pintle hollow cone swirl layout and a closed cap multijet design. In the second part of the paper the used experimental high pressure dynamic test equipment is discussed. Then the results obtained by the use of phase illuminated visualisation techniques and phase Doppler analysis as well as by a 3D CFD approach are presented. The paper concludes by relating the spray patterns and the associated droplet penetration velocities, produced by the different nozzle types, to the combustion chamber layout and to the possible manufacturing precision requirements for each nozzle type.