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During gasoline direct injection (GDI) in spark ignition engines, droplets may hit piston or liner surfaces and be rebounded or deposit in the liquid phase as wallfilm. This may determine slower secondary atomization and local enrichments of the mixture, hence be the reason of increased unburned hydrocarbons and particulate matter emissions at the exhaust. Complex phenomena indeed characterize the in-cylinder turbulent multi-phase system, where heat transfer involves the gaseous mixture (made of air and gasoline vapor), the liquid phase (droplets not yet evaporated and wallfilm) and the solid walls. A reliable 3D CFD modelling of the in-cylinder processes, therefore, necessarily requires also the correct simulation of the cooling effect due to the subtraction of the latent heat of vaporization of gasoline needed for secondary evaporation in the zone where droplets hit the wall. The related conductive heat transfer within the solid is to be taken into account.

In the last years, increasing concerns about environmental pollution and fossil sources depletion led transport sectors research and development towards the study of new technologies capable to reduce vehicles emissions and fuel consumption. Direct-injection systems (DI) for internal combustion engines propose as an effective way to achieve these goals. This technology has already been adopted in Gasoline Direct Injection (GDI) engines and, lately, a great interest is growing for its use in natural gas fueling, so increasing efficiency with respect to port-fuel injection ones. Alone or in combination with other fuels, compressed natural gas (CNG) represents an attractive way to reduce exhaust emission (high H/C ratio), can be produced in renewable ways, and is more widespread and cheaper than gasoline or diesel fuels. Gas direct-injection process involves the occurrence of under-expanded jets in the combustion chamber.

Very high pressures for injecting gasoline in internal combustion (i.c.) engines are recently explored for improving the air/fuel mixing process in order to control unburned hydrocarbons (UBHC) and particulate matter emissions such as for investigating new combustion concepts. The challenge remains the improvement of the spray parameters in terms of atomization, smaller droplets and their spread in the combustion chamber in order to enhance the combustion efficiency. In this framework, the raise of the injection pressure plays a key role in GDI engines for the trade-off of CO2 vs other pollutant emissions. This study aims contributing to the knowledge of the physical phenomena and mechanisms occurring when fuel is injected at ultra-high pressures for mapping and controlling the mixture formation.

Today, Direct-Injection systems are widely used on Spark-Ignition engines in combination with turbo-charging to reduce the fuel-consumption and the knock risks. In particular, the spread of Gasoline Direct Injection (GDI) systems is mainly related to the use of new generations of multi-hole, high-pressure injectors whose characteristics are quite different with respect to the hollow-cone, low-pressure injectors adopted in the last decade. This paper presents the results of an experimental campaign conducted on the spray produced by a GDI six-holes injector into a constant volume vessel with optical access. The vessel was filled with air at atmospheric pressure. Different operating conditions were considered for an injection pressure ranging from 3 to 20 MPa. For each operating condition, spray images were acquired by a CCD camera and then post processed to evaluate the spray penetration and cone angles.

This paper is focused on the development and application of a CFD methodology that can be applied to predict the fuel-air mixing process in stratified charge, sparkignition engines. The Eulerian-Lagrangian approach was used to model the spray evolution together with a liquid film model that properly takes into account its effects on the fuel-air mixing process into account. However, numerical simulation of stratified combustion in SI engines is a very challenging task for CFD modeling, due to the complex interaction of different physical phenomena involving turbulent, reacting and multiphase flows evolving inside a moving geometry. Hence, for a proper assessment of the different sub-models involved a detailed set of experimental optical data is required. To this end, a large experimental database was built by the authors.

Mixture formation is fundamental for the development of the combustion process in internal combustion engines, for the energy release, the consumption, and the pollutant formation. Concerning the spark ignition engines, the direct injection technology is being considered as an effective mean to achieve the optimal air-to-fuel ratio distribution at each operating condition, either through charge stratification around the spark plug and stoichiometric mixture under the high power requirements. Due to the highest injection pressures, the impact of a spray on the piston or on the cylinder walls causes the formation of liquid film (wall-film) and secondary atomization of the droplets. The wall-film could have no negligible size, especially where the mixture formation is realized under a wall-guided mode. The present work aims to report the effects of the ambient pressure and wall temperature on the macroscopic parameters of the spray impact on a wall.

In spark ignition engines, the nozzle design, fuel pressure, injection timing, and interaction with the cylinder/piston walls govern the evolution of the fuel spray inside the cylinder before the start of combustion. The fuel droplets, hitting the surface, may rebound or stick forming a film on the wall, or evaporate under the heat exchange effect. The face wetting results in a strong impact on the mixture formation and emission, in particular, on particulate and unburned hydrocarbons. This paper aims to report the effects of the injection pressure and wall temperature on the macroscopic behavior, atomization, and vaporization of impinging sprays on the metal surface. A mono-component fuel, iso-octane, was adopted in the spray-wall studies inside an optically-accessible quiescent vessel by imaging procedures using a Z-shaped schlieren-Mie scattering set-up in combination with a high-speed C-Mos camera.

In the aim of reducing CO2 emissions and fuel consumption, the improvement of the diesel engine performance is based on the optimization of the whole combustion system efficiency. The focus of new technological solutions is devoted to the optimization of thermodynamic efficiency especially in terms of reduction of losses of heat exchange. In this context, it is required a continuous development of the engine combustion system, first of all the injection system and in particular the nozzle design. To this reason in the present paper a new concept of an open nozzle spray was investigated as a possible solution for application on diesel engines. The study concerns some experimental and numerical activities on a prototype of an open nozzle. An external supplier provided the prototypal version of the injector, with a dedicated piezoelectric actuation system, and with an appropriate choice of geometrical design parameters.

A detailed understanding of Gasoline Direct Injection (GDI) techniques applied to spark-ignition (SI) engines is necessary as they allow for many technical advantages such as increased power output, higher fuel efficiency and better cold start performances. Within this context, the extensive validation of multi-dimensional models against experimental data is a fundamental task in order to achieve an accurate reproduction of the physical phenomena characterizing the injected fuel spray. In this work, simulations of different Engine Combustion Network (ECN) Spray G conditions were performed with the Lib-ICE code, which is based on the open source OpenFOAM technology, by using a RANS Eulerian-Lagrangian approach to model the ambient gas-fuel spray interaction.

This paper reports an experimental and numerical investigation of the spray structure development for pure gasoline fuel and two different ethanol-gasoline blends (10% and 85% ethanol). A numerical methodology has been developed to improve the prediction of the pure and blends fuel spray. The fuel sprays have been simulated by means of a 3D-CFD code, adopting a multi-component approach for the fuel simulations. The vaporization behavior of the real fuel has been improved testing blends of 7 hydrocarbons and a reduced multi-component model has been defined in order to reduce the computational cost of the CFD simulations. Particular care has been also dedicated to the modeling of the atomization and secondary breakup processes occurring to the GDI sprays. The multi-hole jets have been simulated by means of a new atomization approach combined with the Kelvin-Helmholtz/Rayleigh-Taylor hybrid model.

In recent years, due to the growing problem of environmental pollution and climate change internal combustion engine stroke volume size has been reduced. The use of down-sized engines provides benefit for reducing emissions and fuel consumption especially at the inner city driving conditions. However, when the engine demands additional power, utilizing a turbocharging system is required. This study is a joint work of Istituto Motori CNR with Automotive Laboratory of Mechanical Engineering Faculty of Istanbul Technical University (ITU) and the objective of this study was devoted to increase the understanding of various engine operating conditions on emissions, especially at low load. The trade-off between Nitrogen Oxide (NOx) and Particulate Matter (PM) emissions in a Diesel engine has been examined depending on turbocharging rates and the rate of Exhaust Gas Recirculation (EGR) applied.

The aim of the present work is the study of the combustion process in Gasoline Direct Injection (GDI) engine fuelled with ethanol mixed with gasoline at percentages of 10 and 85. The characterization has been made in terms of performance and emission for different injection pressure conditions and the results correlated to the unperturbed non-evaporating evolution of the fuel injected in a pressurized quiescent vessel. Measurements were performed in the optically accessible combustion chamber made by modifying a real 4-stroke, 4-cylinder, high performance GDI engine. The cylinder head was instrumented by using an endoscopic system coupled to high spatial and temporal resolution camera in order to allow the visualization of the fuel injection and the combustion process. The engine is equipped with solenoid-actuated six-hole GDI injectors, 0.14 mm hole diameter, 9.0 g/s @ 10 MPa static flow.

The combustion quality in modern diesel engines depends strictly on the quality of the air-fuel mixing and, in turn, from the quality of spray atomization process. So air-fuel mixing is strongly influenced by the injection pressure, geometry of the nozzle duct and the hydraulic characteristics of the injector. In this context, spray concepts alternative to the conventional multi-hole nozzles could be considered as solutions to the extremely high injection pressure increase to assure a higher and faster fuel-air mixing in the piston bowl, with the final target of increasing the fuel efficiency and reducing the engine emissions. The study concerns an experimental depiction of a spray generated through a prototype high-pressure hollow-cone nozzle, under evaporative and non-evaporative conditions, injecting the fuel in a constant-volume combustion vessel controlled in pressure and temperature up to engine-like gas densities in order to measure the spatial and temporal fuel patterns.

The use of Gasoline Direct Injection (GDI) continuously increases due to the growing demand of efficiency and power output for i.c. engines. The optimization of the fuel injection process is essential to prepare an air-fuel mixture capable to promote efficient combustion, reduced fuel consumption and pollutant emissions. Good spray atomization facilitates fuel evaporation in i.c. engines thus contributing to the fuel economy and lowering the emissions. One of the key features of a multi-hole injector is to provide an optimal spray pattern in the combustion chamber and a good mixture homogenization considering the engine-specific characteristics such fuel mass-flow rate, cylinder geometry, injector position, and charge motion. This work aims to investigate the injection processes of an eight-hole direct-injection gasoline injector from the Engine Combustion Network (ECN) effort on gasoline sprays (Spray G, serial #19).

Gasoline direct injection (GDI) combustion with un-throttled lean stratified operation allows to reduce engine toxic emissions and achieve significant benefits in terms of fuel consumption. However, use of gasoline stratified charges can lead to several problems, such as a high cycle-to-cycle variability and increased particle emissions. Use of multiple injection strategies allows to mitigate these problems, but it requires the injection of small fuel amounts forcing the traditional solenoid injectors to work in their “ballistic” region, where the correlation between coil energizing time and injected fuel amount becomes highly not linear. In the present work a closed-loop control system able to manage the delivery of small quantities of fuel has been introduced. The control system is based on a particular feature found on the coil voltage command signal during the de-energizing phase.

In internal combustion engines, the direct injection at high pressures produces a strong impact of the fuel on the combustion chamber wall, especially in small-bore sizes used for passenger cars. This effect is relevant for the combustion process resulting in an increase of the pollutant emissions and in a reduction of the engine performances. This paper aims to report the effects of the injection pressure and wall temperature on the macroscopic behavior and atomization of the impinging sprays on the wall. The gasoline spray-wall interaction was characterized inside an optically accessible quiescent chamber using a novel make ready Z-shaped schlieren-Mie scattering set-up using a high-speed C-Mos camera as imaging system. The arrangement was capable to acquire alternatively the schlieren and Mie-scattering images in a quasi-simultaneous fashion using the same line-of-sight.

The increasing diffusion of gasoline direct injection (GDI) engines requires a more detailed and reliable description of the phenomena occurring during the fuel injection process. As well known the thermal and fluid-dynamic conditions present in the combustion chamber greatly influence the air-fuel mixture process deriving from GDI injectors. GDI fuel sprays typically evolve in wide range of ambient pressure and temperatures depending on the engine load. In some particular injection conditions, when in-cylinder pressure is relatively low, flash evaporation might occur significantly affecting the fuel-air mixing process. In some other particular injection conditions spray impingement on the piston wall might occur, causing high unburned hydrocarbons and soot emissions, so currently representing one of the main drawbacks of GDI engines.

In the next future, improvements of direct injection systems for spark-ignited engines are necessary for the potential reductions in fuel consumptions and exhaust emissions. The admission and spread of the fuel in the combustion chamber is strictly related to the injector design and performances, such as to the fuel and environmental pressure and temperature conditions. In this paper the spray characterization of a GDI injector under normal and flash-boiling injection conditions has been investigated. The paper is mainly focused both on the capability of the injection apparatus/temperatures controller system to realize flash-boiling conditions, and the diagnostic setup to catch the peculiarities of the spray behavior. The work aims reporting the spray characterization under normal and flash-boiling conditions.

The work analyses, from both an experimental and a numerical point of view, the impingement of a spray generated from a GDI injector on a hot solid wall. The temperature of the surface is identified as an important parameter affecting the outcome after impact. A gasoline spray issuing from a customized single-hole injector is characterized in a quiescent optically-accessible vessel as it impacts on an aluminum plate placed at 22.5 mm from the injector tip. Optical investigations are carried out at atmospheric back-pressure by a direct schlieren optical set-up using a LED as light source. A synchronized C-Mos high-speed camera captures cycle-resolved images of the evolving impact. The spatial and temporal evolution of the liquid and vapor phases are derived. They serve to define a data base to be used for the validation of a properly formulated 3D CFD model suitable to describe the impact of the fuel on the piston head in a real engine.

The regulations about pollutant emissions imposed by Community’s laws encourage the investigation on the combustion optimization in modern engines and in particular in those adopting the gasoline direct injection (GDI) or direct injection spark-ignited (DISI) configuration. It is known that the piston head and cylinder surface temperatures, coupled with the fuel injection pressure, strongly influence the interaction between droplets of injected fluid and the impinged wall. In the present study, the Infrared (IR) thermography is applied to investigate the thermal footprint of an iso-octane spray generated by a multi-hole GDI injector impinging on a heated thin foil. The experimental apparatus includes an Invar foil (50 μm in thickness) heated by Joule effect, clamped within a rigid frame, and the GDI injector located 11 mm above the surface.