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The aim of the paper is the comparison of the injection process with different fuels, i.e. a standard diesel fuel and a pure biodiesel. Multiphase cavitating flows inside diesel nozzles are analyzed by means of unsteady CFD simulations using a two-fluid approach with consideration of bubble dynamics, on moving grids from needle opening to closure. Two five-hole nozzles with cylindrical and conical holes are studied and their behaviors are discussed taking into account the different properties of the two fuels. Extent of cavitation regions is not much affected by the fuel type. Biodiesel leads to significantly higher mass flow only if the nozzle design induces significant cavitation which extends up to the outlet section and if the injector needle is at high lift. If the internal hole shaping is able to suppress cavitation, the stabilized mass flows are very similar with both fuels.

In the present work, an experimental and numerical analysis of high pressure Diesel spray evolution is carried out in terms of spray momentum flux time history and instantaneous injection rate. The final goal of spray momentum and of injection rate analyses is the evaluation of the nozzle outlet flow characteristics and of the nozzle internal geometry possible influences on cavitation phenomena, which are of primary importance for the spray evolution. Further, the evaluation of the flow characteristics at the nozzle exit is fundamental in order to obtain reliable boundary conditions for injection process 3D simulation. In this paper, spray momentum data obtained in ambient temperature, high counter-pressure conditions at the Perugia University Spray Laboratory are presented and compared with the results of 3D simulations of the momentum rig itself.

This paper implements a coupled approach to integrate the internal nozzle flow and the ensuing fuel spray using a Volume-of-Fluid (VOF) method in the CONVERGE CFD software. A VOF method was used to model the internal nozzle two-phase flow with a cavitation description closed by the homogeneous relaxation model of Bilicki and Kestin [1]. An Eulerian single velocity field approach by Vallet et al. [2] was implemented for near-nozzle spray modeling. This Eulerian approach considers the liquid and gas phases as a complex mixture with a highly variable density to describe near nozzle dense sprays. The mean density is obtained from the Favreaveraged liquid mass fraction. The liquid mass fraction is transported with a model for the turbulent liquid diffusion flux into the gas.

This paper reports investigations on diesel jet transients, accounting for internal nozzle flow and needle motion. The calculations are performed with Large Eddy Simulation (LES) turbulence model by coupling the internal and external multiphase flows simultaneously. Short and multiple injection strategies are commonly used in internal combustion engines. Their features are significantly different from those generally found in steady state conditions, which have been extensively studied in the past, however, these conditions are seldom reached in modern engines. Recent researches have shown that residual gas can be ingested in the injector sac after the end-of-injection (EOI) and undesired dribbles can be produced. Moreover, a new injection event behaves differently at the start-of-injection (SOI) depending on the sac initial condition, and the initial spray development can be affected for the first few tens of μs.

This work involves modeling internal and near-nozzle flows of a gasoline direct injection (GDI) nozzle. The Engine Combustion Network (ECN) Spray G condition has been considered for these simulations using the nominal geometry of the Spray G injector. First, best practices for numerical simulation of the two-phase flow evolution inside and the near-nozzle regions of the Spray G injector are presented for the peak needle lift. The mass flow rate prediction for peak needle lift was in reasonable agreement with experimental data available in the ECN database. Liquid plume targeting angle and liquid penetration estimates showed promising agreement with experimental observations. The capability to assess the influence of different thermodynamic conditions on the two-phase flow nature was established by predicting non-flashing and flashing phenomena.

A new camless system (referred to as Hydraulic Valve Control - HVC - system) is in an advanced state of prototyping and development. The present paper aims to support the new incoming activities concerning the possible modifications to the geometrical and mechanical characteristics of the system. The optimization of the new HVC system prototype is done using a multi-objective tool that integrates the hydraulic/mechanical simulator reproducing the physical model, with an optimization software. The latter tool can be used choosing a specific approach among different probabilistic mathematical models; the Genetic Algorithm approach was chosen to achieve the goal of the present study. The paper describes design optimization of the pilot stage of the actuator for given characteristics of the power stage and of the poppet valve.

In order to improve understanding of the primary atomization process for diesel-like sprays, a collaborative experimental and computational study was focused on the near-nozzle spray structure for the Engine Combustion Network (ECN) Spray D single-hole injector. These results were presented at the 5th Workshop of the ECN in Detroit, Michigan. Application of x-ray diagnostics to the Spray D standard cold condition enabled quantification of distributions of mass, phase interfacial area, and droplet size in the near-nozzle region from 0.1 to 14 mm from the nozzle exit. Using these data, several modeling frameworks, from Lagrangian-Eulerian to Eulerian-Eulerian and from Reynolds-Averaged Navier-Stokes (RANS) to Direct Numerical Simulation (DNS), were assessed in their ability to capture and explain experimentally observed spray details. Due to its computational efficiency, the Lagrangian-Eulerian approach was able to provide spray predictions across a broad range of conditions.

The internal structure of Diesel fuel injectors is known to have a significant impact on the nozzle flow and the resulting spray emerging from each hole. In this paper the three-dimensional transient flow structures inside a Diesel injector is studied under nominal (in-axis) and realistic (including off-axis lateral motion) operating conditions of the needle. Numerical simulations are performed in the commercial CFD code CONVERGE, using a two-phase flow representation based on a mixture model with Volume of Fluid (VOF) method. Moving boundaries are easily handled in the code, which uses a cut-cell Cartesian method for grid generation at run time. First, a grid sensitivity study has been performed and mesh requirements are discussed. Then the results of moving needle calculations are discussed. Realistic radial perturbations (wobbles) of the needle motion have been applied to analyze their impact on the nozzle flow characteristics.

Among variable valve actuation systems, fully flexible systems such as camless devices are the most attractive valvetrains for near-future engines. This paper presents a research activity about an electro-hydraulic camless system for internal combustion engines. The Hydraulic Valve Control (HVC) system uses hydraulic forces to open the valve while a mechanical spring is used for the closure. The system is fed by an hydraulic pump and two pressure regulators which provide two different pressure levels: a high pressure level (approximately 100 bar) for the pilot stage and a low adjustable pressure level (from 20 to 90 bar) for the actuator power stage. The valve opening duration is controlled by varying the timing of the opening signal of the pilot stage; the valve lift is adjusted varying the oil pressure of the power stage. From a general point of view, the HVC system is an open loop device for engine valve actuation.

This paper presents the current research activity about an electro-hydraulic camless valve actuation system for internal combustion engines. From a general point of view, this system (Hydraulic Valve Control - HVC) is an open loop device for engine valve fully flexible camless actuation. In the HVC system, the valve actuation timing and duration are controlled by varying the driving signal of the pilot stage, which is governed by a solenoid, fast-acting, three-way valve; the valve lift is adjusted by varying the oil pressure of the power stage. This system uses hydraulic forces to open the engine valve while a mechanical spring is used for its closure. The HVC key element is a spool valve, which operates as a three way / three position valve. This element is designed in order to ensure the synchronization of its own motion with that of the poppet valve mass-spring system.

This work aims at analyzing the fluid dynamic characteristics of a Ducati 4 valves SI engine, for racing motorcycle, during the intake and compression strokes, focusing on the correlation between steady state flow test data (experiments and simulations) and transient CFD simulation results, including the effect of variable valve actuation strategies with independent intake valve actuation. Several steady state flow test data were available in terms of maps of the discharge, tumble and swirl coefficients, at any combination of asymmetric lifts of the two intake valves. From these steady state data it can be argued that asymmetric strategies could enhance engine full load and part load operation characteristics, by exploiting favourable trade off occurring between the opposing needs for high mass flow rate and high charge motion intensity.

This paper presents the further development of an electro-hydraulic camless valve actuation system for internal combustion engines. The system (Hydraulic Valve Control - HVC) is an open loop device for engine valve fully flexible camless actuation. Valve timing and duration are controlled by a pilot stage governed by a solenoid, fast-acting, three-way valve. Valve lift is controlled by varying the oil pressure of the power stage. The system exploits an energy recovery working principle that plays a significant role in reducing the power demand of the whole valve train. In the present paper a new HVC actuator design is presented and its performances in terms of valve lift profile, repeatability and landing are discussed. Experimental data obtained by the application of the HVC system to a motored, single-cylinder research engine have been used to support the numerical evaluation of the potentialities of non-conventional valve actuation in engine part-load operation.

In the present paper, a detailed numerical and experimental analysis of a spray momentum flux measurement device capability is presented. Particular attention is devoted to transient, engine-like injection events in terms of spray momentum flux measurement. The measurement of spray momentum flux in steady flow conditions, coupled with knowledge of the injection rate, is steadily used to estimate the flow mean velocity at the nozzle exit and the extent of flow cavitation inside the nozzle in terms of a velocity reduction coefficient and a flow section reduction coefficient. In the present study, the problem of analyzing spray evolution in short injection events by means of jet momentum flux measurement was approached. The present research was based on CFD-3D analysis of the spray-target interaction in a momentum measurement device.

In this paper an experimental analysis is carried out to evaluate the dependence of the flow characteristics in the intake system of a high performance 4 valve, Spark Ignition Internal Combustion Engine, on the experimental conditions at the steady flow test bench. Experimental tests are performed at different pressure levels on a Ducati Corse racing engine head, to measure the Discharge Coefficient Cd and the Tumble Coefficient NT, expanding the work already presented in a previous work by the same research group: with a new test bench, the maximum test pressure level is increased up to 24 kPa, while differently-shaped tumble adaptors are used to evaluate Nt. The study is aimed at determining the influence of the test pressure on Cd and NT measurements, and in particular of the tumble adaptor shape.

In this work an experimental analysis is performed to evaluate the influence of different flow bench test conditions and system configurations on the flow characteristics in the intake system of a high performance 4-valve, SI Internal Combustion Engine: valve lift, test pressure drop, throttle valve aperture, throttle valve opening direction in respect to the intake system layout (i.e. clockwise/counterclockwise), presence of the tumble adaptor. To this aim, experimental tests are performed on a Ducati Corse racing engine cylinder head, by measuring the discharge coefficient and the tumble coefficient. The several experimental data obtained by combining the different operational and geometrical parameters are analysed and discussed.

This work investigates the effects of cavitation on spray characteristics by comparing measurements of liquid and vapor penetration as well as ignition delay and lift-off length. A smoothed-inlet, converging nozzle (nominal KS1.5) was compared to a sharp-edged nozzle (nominal K0) in a constant-volume combustion vessel under thermodynamic conditions consistent with modern compression ignition engines. Within the near-nozzle region, the K0 nozzle displayed larger radial dispersion of the liquid as compared to the KS1.5 nozzle, and shorter axial liquid penetration. Moving downstream, the KS1.5 jet growth rate increased, eventually reaching a growth rate similar to the K0 nozzle while maintaining a smaller radial width. The increasing spreading angle in the far field creates a virtual origin, or mixing offset, several millimeters downstream for the KS1.5 nozzle.

A two-step simulation methodology was applied for the computation of the injector nozzle internal flow and the spray evolution in diesel engine-like conditions. In the first step, the multiphase cavitating flow inside injector nozzle is calculated by means of unsteady CFD simulation on moving grids from needle opening to closure. A non-homogeneous Eulerian multi-fluid approach - with three phases i.e. liquid, vapor and air - has been applied. Afterward, in the second step, transient data of spatial distributions of velocity, turbulent kinetic energy, dissipation rate, void fraction and many other relevant properties at the nozzle exit were extracted and used for the subsequent Lagrangian spray calculation. A primary break-up model, which makes use of the transferred data, is used to initialize droplet properties within the hole area.

An extensive numerical study of two-phase flow inside the nozzle holes and the issuing jets for a multi-hole direct injection gasoline injector is presented. The injector geometry is representative of the Spray G nozzle, an eight-hole counter-bored injector, from the Engine Combustion Network (ECN). Homogeneous Relaxation Model (HRM) coupled with the mixture multiphase approach in the Eulerian framework has been utilized to capture the phase change phenomena inside the nozzle holes. Our previous studies have demonstrated that this approach is capable of capturing the effect of injection transients and thermodynamic conditions in the combustion chamber, by predicting phenomenon such as flash boiling. However, these simulations were expensive, especially if there is significant interest in predicting the spray behavior as well.

The present work concerns the analysis of a concept for a new variable valve actuation system for internal combustion engines, denoted HVC (Hydraulic Valve Control system). The system is an electro-hydraulic device which aims at minimizing the power consumption required for the valve actuation. Unlike lost motion devices, where the excess pumped oil is wasted in order to control the lift profile, the HVC system uses a reduced quantity of energy to ensure the actual lift profile. For that reason interesting potentialities to increase the global fuel conversion efficiency of the engine are expected, in addition to the benefits deriving from the control flexibility. The HVC system has been modeled by means of an hydraulic simulation tool, useful for the dynamic analysis of mechanical and hydraulic systems. In this work the main elements of the device will be described and their relevant modeling parameters will be discussed.

This present work is aimed to the analysis of the possible advantages that could be obtained exploiting Variable Valve Actuation strategies in an high performance engine head. A set of experimental tests was carried out to obtain maps of the discharge, tumble and swirl coefficients, at any combination of asymmetric lifts of the two intake valves. The results show that asymmetric strategies could allow engine part load operation characterized by enhanced tumble/swirl generation, while keeping the same effective flow area of conventional two valves symmetric lift. Numerical simulations allowed a deeper understanding of the tumble motion characteristics at different lift combinations, and in particular for asymmetric low lifts cases where the lack of the typical abrupt tumble rising zone was noted.