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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.

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.

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.

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).

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.

Compressed Natural Gas (CNG) is regarded as a promising fuel for spark-ignited (SI) internal combustion engines (ICE) to improve engine thermal efficiency and reduce both carbon dioxide and pollutant emissions. Significant advantages of CNG are higher-octane number, higher hydrogen to carbon ratio, and lower energy-specific CO2 emissions compared with gasoline. More, it can be produced in renewable ways, and is more widespread and cheaper than conventional liquid fossil fuels. In this regard, the direct injection of CNG engines can be considered a promising technology for highly efficient and low-emission future engines. This work reports an experimental and numerical characterization of high-pressure methane jets from a multi-hole injector for direct injection engines.

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.

The combustion of fossil-based fuels in ICEs, resulting in a huge amount of greenhouse gases (GHG) and leading to an immense global temperature rise, are the root causes of the more stringent emission legislations to safeguard health and that encourage further investigations on alternative carbon-neutral fuels. In this respect, the hydrogen has been considered as one of the potential clean fuels because of its zero-carbon nature. The current development of hydrogen-based ICEs focuses on the direct injection (DI) strategy as it allows better engine efficiency than the port fuel injection one. The behavior of the fuel jet is a fundamental aspect of the in-cylinder air-fuel mixing ratio, affecting the combustion process, the engine performances, and the pollutants emissions. In the present study, comprehensive investigations on the hydrogen jet behavior, generated by a Compressed Hydrogen Gas (CHG) injector under different operative conditions, were performed.

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 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 use of biodiesel as alternative to fossil fuel for light duty CI engines to reduce greenhouse gas emissions was widely investigated. However, poor stability of biodiesel - diesel mixture limits the use of biodiesel to low volume concentrations. This paper presents the results concerning the use of a novel fuel additive package containing antioxidant (AS), pour-point depressant (D) and biocide (Bi) with the aim to increase the quality and amount of biodiesel in the diesel-biodiesel blends. Some of the goals are linked to the degradative effects due to free radicals oxidation, contamination by water and microorganisms. The interaction between two different additive packages and two biodiesel (soybean and rapeseed) - diesel blends at 20% in volume was investigated. Optical studies have been performed to characterize the spatial and temporal spray evolution both in a high pressure quiescent vessel and in an optically-accessible single-cylinder 2-stroke CI engine.

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.

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.

The Direct Injection (DI) of gasoline in Spark Ignition (SI) engines is very attractive for fuel economy and performance improvements in spark ignition engines. Gasoline direct injection (GDI) offers the possibility of multi-mode operation, homogeneous and stratified charge, with benefits respect to conventional SI engines as higher compression ratio, zero pumping losses, control of the ignition process at very lean air-fuel mixture and good cold starting. The impingement of liquid fuel on the combustion chamber wall is generally one of the major drawbacks of GDI engines because its increasing of HC emissions and effects on the combustion process; in the wall guided engines an increasing attention is focusing on the fuel film deposits evolution and their role in the soot formation. Hence, the necessity of a detailed understanding of the spray-wall impingement process and its effects on the fuel distribution. The experimental results provide a fundamental data base for CFD predictions.