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The selection and tuning of the Fuel Injection System (FIS) are among the most critical tasks for the automotive diesel engine design engineers. In fact, the injection strongly affects the combustion phenomena through which controlling a wide range of related issues such as pollutant emissions, combustion noise and fuel efficiency becomes feasible. In the scope of the engine design optimization, the simulation is an efficient tool in order to both predict the key performance parameters of the FIS, and to reduce the amount of experiments needed to reach the final product configuration. In this work a complete characterization of a solenoid ballistic injector for a Light-Duty Common Rail system was therefore implemented in a commercially available one-dimensional computational software called GT-SUITE. The main phenomena governing the injector operation were simulated by means of three sub-models (electro-magnetic, hydraulic and mechanical).

Nowadays, injection rate shaping and multi-pilot events can help to improve fuel efficiency, combustion noise and pollutant emissions in diesel engine, providing high flexibility in the shape of the injection that allows combustion process control. Different strategies can be used in order to obtain the required flexibility in the rate, such as very close pilot injections with almost zero Dwell Time or boot shaped injections with optional pilot injections. Modern Common-Rail Fuel Injection Systems (FIS) should be able to provide these innovative patterns to control the combustion phases intensity for optimal tradeoff between fuel consumption and emission levels.

In the present paper the results of an experimental and numerical analysis of a common-rail, high pressure Diesel spray evolving in high counter pressure conditions is reported. The experimental study was carried out mainly in terms of spray momentum flux indirect measurement by the spray impact method; the measurement of the impact force time-histories, along with the CFD analysis of the same phenomenon, gave interesting insight in the internal spray structure. As well known, the overall spray structure momentum flux along with the injection rate measurements can be used to derive significant details about the in-nozzle flow and cavitation phenomena intensity. The same global spray momentum and momentum flux measurement can be useful in determining the jet-to-jet un-uniformities also in transient, engine-typical injection conditions which can assist in the matching process between the injection system and the combustion chamber design.

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.

The injection rate modulation and the spray characteristics are determining factors for the quality of mixture formation when applying GDI. Their variation with load and speed is a basic criterion for the adaptability of a type of injection system to an engine with known requirements. The increased interest for the utilization of regenerative fuels - such as methanol obtained from biomass - as well as the success of previous utilization scenarios of variable gasoline/methanol mixture using manifold injection formed the base of the present analysis: the paper describes the results concerning injection performances and spray characteristics when using gasoline/methanol mixtures with different ratios in a direct injection system with high pressure modulation. The results are compared for different parameters of the injection systems as follows: injection volume, injector opening pressure, needle lift, pintle/seat geometry.

A hybrid model for the atomization of Diesel sprays was developed [1]. The model was added to the KIVA code to better simulate spray evolution. Different implementation for low-medium and high injection pressure sprays are performed. It has already been validated for the low-pressure case [1,2] and in this work it was tested for high injection pressure systems, in a vessel at ambient conditions. It distinguishes between jet primary breakup and droplet secondary breakup. For the latter distinct models are used, as the droplet Weber number changes in the various regimes, in order to take into account the effects of the different relevant forces. For high pressure Diesel spray the effects of jet turbulence, cavitation and nozzle flow on liquid core primary breakup must be considered. Due to the high droplet velocity the catastrophic secondary breakup regime may occur.

The recent introduction of electronic controlled, high pressure injection systems has deeply changed the scenario for light duty, automotive diesel engines. This change is mainly due to the enhanced flexibility in obtaining the desired injection law (time history and injected fuel quantity), while high injection pressures also favour a suitable mixture formation. This results in higher engine performance (efficiency and power) and in better pollutant emissions control. At the same time, in order to reduce the greenhouse gases net production, research is analyzing alternative resources, such as bio-derived fuels. In particular, methyl esters derived by different vegetable oils are characterized by high cetane numbers and very small sulfur content. The present work reports the results of a comparative analysis performed on a modern DI, common-rail, turbocharged engine by using three different bio-derived fuels (rape seed, soybean, waste cooked oil) and conventional fossil diesel fuel.

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.

In order to evaluate the potentialities of bioderived diesel fuels, the effect of fueling a 1.9 l displacement HSDI automotive Diesel engine with biodiesel and fossil/biodiesel blend on its emission and combustion characteristics has been investigated. The fuels tested were a typical European diesel, a 50% biodiesel blend in the reference diesel, and a 100% biodiesel, obtained by mixing rape seed methyl ester (RME) and recycled cooking oil (CME). Steady state tests were performed at two different engine speeds (2500 and 4000 rpm), and for a wide range of loads, in order to evaluate the behavior of the fuels under a large number of operating conditions. Engine performance and exhaust emissions were analyzed, along with the combustion process in terms of heat release analysis. Experimental evidences showed appreciably lower CO and HC specific emissions and a substantial increase in NOx levels. A significant reduction of smoke emissions was also obtained.

The potentialities in terms of engine performance and emissions reduction of pure biodiesel were examined on a Common Rail HSDI Diesel engine, trying to define a proper tuning of the injection strategies to bio-fuel characteristics. An experimental investigation was therefore carried out on a typical European passenger car Diesel engine, fuelled with a soybean oil derived biodiesel. A standard European diesel fuel was also used as a reference. In particular, the effects of an equal relative air/fuel ratio at full load condition were analysed; further, a sensitivity study on the outcome of the pilot injection timing and duration at part load on engine emissions was performed. Potentialities in recovering the performance gap between fossil fuel and biodiesel and in reducing NOx specific emissions, affecting only to a limited extent the biodiesel emission benefit in terms of CO, HC and FSN, were highlighted.

In order to optimize gasoline direct injection combustion systems, a very accurate control of the fuel flow rate from the injector must be attained, along with appropriate spray characteristics in terms of drop sizing and jets global penetration/diffusion in the combustion chamber. Injection rate measurement is therefore one of the crucial tasks to be accomplished in order both to develop direct injection systems and to properly match them with a given combustion system. Noticeably, the hydraulic characteristics of GDI injectors should be determined according to a non-intrusive measuring approach. Unfortunately, the operation of all conventional injection analyzers requires the injection in a volume filled with liquid and the application of a significant counter-pressure downstream of the injector. This feature prevents any operation with low pressure injection systems such as PFIs.

In recent years, the GDI (Gasoline Direct Injection) technology has significantly spread over the automotive market under the continuous push toward the adoption of combustion systems featuring high thermodynamic conversion efficiency and moderate pollutant emissions. Following this path, the injection pressure level has been progressively increased from the initial 5-15 MPa level nowadays approaching 35 MPa. The main reason behind the progressive injection pressure increase in GDI engines is the improved spray atomization, ensuring a better combustion process control and lower soot emissions. On the other hand, increasing injection pressure implies more power absorbed by the pumping system and hence a penalty in terms of overall efficiency. Therefore, the right trade-off has to be found between soot formation tendency reduction thanks to improved atomization and the energetic cost of a high pressure fuel injection system.

The present paper describes the effect of thermal conditions on the hydraulic behavior of Diesel common rail injectors, with a particular focus on low temperatures for fuel and injector body. The actual injection system thermal state can significantly influence both the injected quantity and the injection shape, requiring proper amendments to the base engine calibration in order to preserve the combustion efficiency and pollutant emissions levels. In particular, the introduction of the RDE (Real Driving Emission) test cycle widens the effective ambient temperature range for the homologation cycle, this way stressing the importance of the thermal effects analysis. An experimental test bench was developed in order to characterize the injector in an engine-like configuration, i.e. fuel pump, piping, common rail, pressure control system and injectors.

In the present paper, the results of a detailed experimental analysis of a GDI spray based on Imaging, Phase Doppler Anemometry data and Momentum Flux distribution measurement are presented and discussed. The GDI system used is a three-hole research injector, operated in an injection pressure range of 50 bar to 150 bar. Spray Imaging is performed according to an ensemble average approach, acquiring images at different timings during the injection process; the resulting penetration and cone angle time-histories allow a quantitative description of the spray structure shape. Momentum flux distribution data are obtained by means of a dedicated test bench which detects the impact force of small spray portions. The sensing device is moved in different positions inside the spray structure, with the acquired force transients averaged on several injection events.

The effects of using blended renewable diesel fuel (30% vol.), obtained from Rapeseed Methyl Ester (RME) and Hydrotreated Vegetable Oil (HVO), in a Euro 5 small displacement passenger car diesel engine have been evaluated in this paper. The hydraulic behavior of the common rail injection system was verified in terms of injected volume and injection rate with both RME and HVO blends fuelling in comparison with commercial diesel. Further, the spray obtained with RME B30 was analyzed and compared with diesel in terms of global shape and penetration, to investigate the potential differences in the air-fuel mixing process. Then, the impact of a biofuel blend usage on engine performance at full load was first analyzed, adopting the same reference calibration for all the tested fuels.

The interest towards hydrogen fueling in internal combustion engines (ICEs) is rapidly growing, due to its potential impact on the reduction of the carbon footprint of the road transportation sector in a short-term scenario. While the conversion of the existing fleet to a battery-electric counterpart is highly debated in terms of both technical feasibility and life-cycle-based environmental impact, automotive researchers and technicians are exploring other solutions to reduce, if not to nullify, the carbon footprint of the existing ICE fleet. Indeed, ICE conversion to “green” fuels is seen as a promising short-term solution which does not require massive changes in powertrain production and end-of-life waste management. To better evaluate potentials and challenges of hydrogen fueling, a clear understanding of fuel injection and mixture formation prior to combustion is mandatory.

In an earlier study, a novel type of diesel fuel injector was proposed. This prototype injects fuel via porous (sintered) micro pores instead of via the conventional 6-8 holes. The micro pores are typically 10-50 micrometer in diameter, versus 120-200 micrometer in the conventional case. The expected advantages of the so-called Porous Fuel Air Mixing Enhancing Nozzle (PFAMEN) injector are lower soot- and CO2 emissions. However, from previous in-house measurements, it has been concluded that the emissions of the porous injector are still not satisfactory. Roughly, this may have multiple reasons. The first one is that the spray distribution is not good enough, the second one is that the droplet sizing is too big due to the lack of droplet breakup. Furthermore air entrainment into the fuel jets might be insufficient. All reasons lead to fuel rich zones and associated soot formation.

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.

Ducted Fuel Injection (DFI) is a new technology recently developed with the aim of reducing soot emission formation in diesel compression ignition engines. DFI concept consists of the injection of fuel spray through a small duct located downstream of the injector nozzle leaving a certain gap, the so-called Stand-off distance. Currently, CFD modelers have investigated its performance using classical spray modeling techniques such as the Discrete Drops Method (DDM). However, as discussed in the literature, this type of technique is inappropriate when applied to dense jets as those occurring in diesel sprays, especially in the near-nozzle region (where the duct is placed). Therefore, considering a more appropriate modeling technique for such a problem is mandatory. In this research work, an Eulerian single-fluid diffuse-interface model called Σ-Y and implemented in the OpenFOAM framework is utilized for the simulation of non-reacting conditions.