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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.

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.

A two-equation Zonal-DES (ZDES) approach has been recently proposed by the authors as a suitable hybrid URANS/LES turbulence modeling alternative for Internal Combustion Engine flows. This approach is conceptually simple, as it is all based on a single URANS-like framework and the user is only required to explicitly mark which parts of the domain will be simulated in URANS, DES or LES mode. The ZDES rationale was initially developed for external aerodynamics applications, where the flow is statistically steady and the transition between zones of different types usually happens in the URANS-to-DES or URANS-to-LES direction. The same “one-way” transition process has been found to be fairly efficient also in steady-state internal flows with engine-like characteristics, such as abrupt expansions or intake ports with fixed valve position.

The onset of cavitating conditions inside the nozzle of diesel injectors is known to play a major role on spray characteristics, especially on jet penetration and break-up. In this work, for the first time a Direct Numerical Simulation (DNS) based on the Lattice Boltzmann Method (LBM) is applied to study the fluid dynamic field inside the nozzle of a cavitating diesel injector. The formation of the cavitating region is determined via a multi-phase approach based on the Shan-Chen Equation of State and its most recent enhancements. The evolution of cavitation bubbles is followed and the characteristic numbers, i.e., Cavitation Number (CN) and discharge coefficient (Cd) are evaluated. The results obtained by the LBM simulation are compared to both numerical and experimental data present in literature.

An engine head of a common rail direct injection engine with three in line cylinders for Light Transportation Vehicle (LTV) applications has been analyzed and optimized by means of uncoupled CFD and FEM simulations in order to assess the strength of the components. This paper deals with a structural stress analysis of the cylinder head considering the thermal loads computed through an CFD simulation and a detailed FV heat-transfer analysis. The FE model of the cylinder head includes the contact interaction between the main parts of the cylinder head assembly and it is subjected to the gas pressure, thermal loads and the effects of bolts tightening and valve springs. The results, in term of temperature field, are validated by comparing with those obtained by means of experimental analyses. Then a fatigue assessment of the cylinder head has been performed using a multi-axial fatigue criterion.

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.