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Internal combustion engines performance greatly depends on the air-fuel mixture formation and combustion processes. In gasoline direct injection (GDI) engines, in particular, the impact of the liquid spray on the piston or cylinder walls is a key factor, especially if mixture formation occurs under the so-called wall-guided mode. Impact causes droplets rebound and/or deposition of a liquid film (wallfilm). After being rebounded, droplets undergo what is called secondary atomization. The wallfilm may remain of no negligible size, so that fuel vapor rich zones form around it leading to so-called pool-flames (flames placed in the piston pit), hence to unburned hydrocarbons (HC) and particulate matter (PM) formation. A basic study of the spray-wall interaction is here performed by directing a multi-hole GDI spray against a real shape engine piston, possibly heated, under standard air conditions.

The use of methane as supplement to liquid fuel is one of the solution proposed for the reduction of the internal combustion engine pollutant emissions. Its intrinsic properties as the high knocking resistance and the low carbon content makes methane the most promising clean fuel. The dual fuel combustion mode allows improving the methane combustion acting mainly on the methane slow burning velocity and allowing lean burn combustion mode. An experimental investigation was carried out to study the methane-gasoline dual fuel combustion. Methane was injected in combustion chamber (DI fuel) while gasoline was injected in the intake manifold (PFI fuel). The measurements were carried out in an optically accessible small single-cylinder four-stroke engine. It was equipped with the cylinder head of a commercial 250 cc motorcycles engine representative of the most popular two-wheel vehicles in Europe.

The growing concerns on the emission of particles smaller than 23 nm, which are harmful to human health, lead to the necessity of introducing a regulation for these particles not yet included in the current emission standards. Considering that measurements of concentration of sub-23 nm particles are particularly sensitive to the sampling conditions, it is important to identify an effective assessment procedure. Aim of this paper is the characterization of the effect of the sampling conditions on sub-23 nm particles, emitted by PFI (port fuel injection) and DI (direct injection) spark ignition engines fueled with gasoline, ethanol and a mixture of ethanol and gasoline (E30). The experimental activity was carried out on a 250 cm3 displacement four stroke GDI and PFI single cylinder engines. The tests were conducted at 2000 rpm and 4000 rpm full load, representative of the homologation urban driving cycle.

In the last years, even more attention was paid to the alternative fuels which can allow both reducing the fuel consumption and the pollutant emissions. Among gaseous fuels, methane is considered one of the most interesting in terms of engine application. It represents an immediate advantage over other hydrocarbon fuels leading to lower CO₂ emissions; if compared to gasoline, CH₄ has wider flammable limits and better anti-knock properties, but lower flame speed. The addition of H₂ to CH₄ can improve the already good qualities of methane and compensate its weak points. In this paper a comparison was carried out between CH₄ and different CH₄/H₂ mixtures. The measurements were carried out in an optically accessible small single-cylinder, Port Fuel Injection spark ignition (PFI SI), four-stroke engine. It was equipped with the cylinder head of a commercial 250 cc motorcycle engine representative of the most popular two-wheel vehicles in Europe.

This paper deals with the evaluation of the effect of fuel properties on soot formation in a GDI (gasoline direct injection) engine. Experimental investigation was carried out in an optical 4-stroke small single cylinder engine for two-wheel vehicles. The engine displacement was 250 cc. It was equipped with an elongated piston with a wide sapphire window in the head and a quartz cylinder liner. The engine was fuelled with pure gasoline and ethanol, and ethanol/gasoline blends at 20% v/v, 50% v/v and 85% v/v. Optical techniques based on 2D-digital imaging were used to follow the combustion process and soot formation. Spectroscopic measurements were carried out in order to assess the soot evolution. Radical species such as OH and CH, related to fuel quality and to soot formation/oxidation process, were detected. Measurements were carried out at various engine speeds and loads in order to allow optical measurements and to test the engine in real conditions.

The objective of this paper is the evaluation of the effect of the fuel properties and the comparison of a PFI and GDI injection system on the performances and on particle emission in a Spark Ignition engine. Experimental investigation was carried out in a small single cylinder engine for two wheel vehicles. The engine displacement was 250 cc. It was equipped with a prototype GDI head and also with an injector in the intake manifold. This makes it possible to run the engine both in GDI and PFI configurations. The engine was fuelled with neat gasoline and ethanol, and ethanol/gasoline blends at 10% v/v, 50% v/v and 85% v/v. The engine was equipped of a quartz pressure transducer that was flush-mounted in the region between intake and exhaust valves. Tests were carried out at 3000 rpm and 4000 rpm full load and two different lambda conditions. These engine points were chosen as representative of urban driving conditions.

Gasoline direct injection (GDI) allows knock tendency reduction in spark-ignition engines mainly due to the cooling effect of the in-cylinder fuel evaporation. However, the charge formation and thus the injection timing and strategies deeply affect the flame propagation and consequently the knock occurrence probability and intensity. In particular, split injection allows a reduction of knock intensity by inducing different AFR gradient and turbulent energy distribution. Present work investigates the tendency to knock of a GDI engine at 1500 rpm full load under different injection strategies, single and double injections, obtained delivering the same amount of gasoline in two equal parts, the first during intake, the second during compression stroke. In these conditions, conventional and non-conventional measurements are performed on a 4-stroke, 4-cylinder, turbocharged GDI engine endowed of optical accesses to the combustion chamber.

In this paper, the modifications realized to make optically accessible a commercial high performance spark ignition and direct injection (DI) 4-cylinder engine are reported. The engine has been designed trying to keep as much as possible its thermo-fluid dynamic configuration in order to maintain its performance and emissions. Two optical accesses have been realized in order to interfere as little as possible with the combustion chamber geometry. A first optical access has been achieved in the piston head and a second by inserting an endoscopic fiber probe in the head. Preliminary results demonstrated that this optical assessment responds to the design targets and allowed a characterization of a commercial GDI engine working with homogeneous and stratified charge mode.

Ethanol is the most promising alternative fuel for spark ignition (SI) engines, that is blended with gasoline, typically. Moreover, in the last years great attention is paid to the dual fueling, ethanol and gasoline are injected simultaneously. This paper aims to analyze the better methods, blending or dual fueling in order to best exploit the potential of ethanol in improving engine performance and reducing pollutant emissions. The experimental activity was carried out in a small displacement single cylinder engine, representative of 2-3 wheel vehicle engines or of 3-4 cylinder small displacement automotive engines. It was equipped with a prototype gasoline direct injection (GDI) head. The tests were carried out at 3000, 4000, and 5000 rpm full load. The investigated engine operating conditions are representative of the European homologation urban driving cycle.

The use of direct injection (DI) engines allows a more precise control of the air-fuel ratio, an improvement of fuel economy, and a reduction of exhaust emissions thanks to the ultra-lean combustion due to the charge stratification. These effects can be partially obtained also with an optimized Air Direct Injection that permits to increase the turbulence at low speed and load increasing the combustion stability especially in lean condition. In this paper, a gasoline PFI (named G-PFI), gasoline PFI-methane DI dual fuel (named G-MDF) lean combustion were analyzed. The G-MDF configuration was also compared with a gasoline PFI - air DI (named G-A) configuration in order to distinguish the chemical effect of methane from the direct injection physical effect. The tests were carried out in a small displacement PFI/DI SI engine. The experimental investigation was carried out in a transparent small single-cylinder, spark ignition four-stroke engine.

The in-cylinder direct injection of natural gas can be a further step towards cleaner and more efficient internal combustion engines (ICE). However, the injector design and its characterization, both experimentally and by numerical simulation, is challenging because of the complex fluid dynamics related to gas compressibility and the small length scale. In this work, the under-expanded flow of methane from an outward-opening poppet-valve injector has been experimentally characterized by high-speed schlieren imaging. The investigation has been performed at ambient temperature and pressure and different nozzle pressure ratios (NPR) ranging from 10 to 18. The gaseous jet has been characterized in terms of its macroscale parameters. A scaling-law analysis of the results has been performed. The gas-dynamic structure at the nozzle exit has been also investigated.

The present paper deals with a comprehensive analysis of the knocking phenomenon through experiments and numerical simulations. Conventional and non-conventional measurements are performed on a 4-stroke, 4-cylinder, turbocharged GDI engine. The engine exhibits optical accesses to the combustion chamber. Imaging in the UV-visible range is carried out by means of a high spatial and temporal resolution camera through an endoscopic system and a transparent window in the piston head. This last is modified to allow the view of the whole combustion chamber almost until the cylinder walls, to include the so-called eng-gas zones. Optical data are correlated to in-cylinder pressure-based indicated analyses in a cycle resolved approach.

In the framework of an increasing demand for a more sustainable mobility, where the fuel consumption reduction is a key driver for the development of innovative internal combustion engines, Turbulent Jet Ignition (TJI) represents one of the most promising solutions to improve the thermal efficiency. However, details concerning turbulent jet assisted combustion are still to be fully captured, and therefore the design and the calibration of efficient TJI systems require the support of reliable simulation tools that can provide additional information not accessible through experiments. To this aim, an experimental investigation combined with a 3D-CFD study was performed to analyze the TJI combustion characteristics in a single-cylinder spark-ignition (SI) engine. Firstly, the model was validated against experiments considering stoichiometric mixture at 3000 rpm, wide open throttle operating conditions.

The increased limitations to both NOx and soot emissions have pushed engine researchers to rediscover gasoline engines. Among the many technologies and strategies, gasoline direct injection plays a key-role for improving fuel economy and engine performance. The paper aims to investigate an extremely complex task such as the idle operating engine condition when the engine runs at very low engine speeds and low engine loads and during the warm-up. Due to the low injection pressure and to the null contribution of the turbocharger, the engine condition is far from the standard points of investigation. Taking into account the warm-up engine condition, the analyses are performed with a temperature of the coolant of 50°C. The paper reports part of a combined numerical and experimental synergic activity aiming at the understanding of the physics of spray/wall interaction within the combustion chamber and particular care is used for air/fuel mixing and the combustion process analyses.

Non-intrusive measurements were carried out in an optical spark ignition GDI engine in order to characterize the chemical and physical processes involved using gasoline and bio-ethanol fuel. In particular, an optical 4 strokes small single cylinder engine for two wheel vehicles was used. It was equipped with an elongated piston with a wide sapphire window in the head and quartz cylinder. Exhaust emissions and engine performances were evaluated during the imaging and spectral measurements in order to investigate the spray characteristics and flame propagation with high spatial and temporal resolution. Several engine conditions based on homogeneous charge mixture conditions were investigated considering the effect of injection pressure and ethanol fuel too. The simultaneous use of the high injection pressure and bio-ethanol showed to be a valid answer to reduction of pollutants without worsening the performances.

The growing concerns over the pollutant emissions as well as the depletion of fossil fuel led to the research of advanced combustion mode and alternative fuels for the reduction both of fuel consumption and exhaust emissions. The dual-fuel injection system can be used to improve the engine performance and reduce the fossil fuel consumption performing simultaneously a direct-injection (DI) and a port-fuel-injection (PFI) of different fuels. Ethanol is one of the most promising alternative fuels for SI engines. It offers high anti-knock quality because of the high octane number; moreover, being an oxygenated fuel is very effective in particle emissions reduction. On the other hand, it is characterized by lower energy density mainly because of the low lower heating value (LHV). The aim of the paper is the investigation of the ethanol-gasoline dual fuel combustion on engine performance and emissions.

Improvement of performance and emission of future internal combustion engine for passenger cars is mandatory during the transition period toward their substitution with electric propulsion systems. In middle time, direct injection spark ignition (DISI) engines could offer a good compromise between fuel economy and exhaust emissions. However, abnormal combustion and particularly knock and super-knock are some of the most important obstacles to the improvement of SI engines efficiency. Although knock has been studied for many years and its basic characteristics are clear, phenomena involved in its occurrence are very complex and are still worth of investigation. In particular, the definition of an absolute knock intensity and the precise determination of the knock onset are arduous and many indexes and methodologies has been proposed. In this work, most used methods for knock onset detection from in- cylinder pressure signal have been considered.

Within the context of distributed power generation, small size systems driven by spark ignition engines represent a valid and user-friendly choice, that ensures good fuel flexibility. One issue is that such applications are run at part load for extensive periods, thus lowering fuel economy. Employing an inverter (fitted between the generator and load) allows engine operation within a wide range of crankshaft rotational velocity, therefore improving efficiency. For the purpose of evaluating the benefits of this technology within a co-generation framework, two configurations were modeled by using the GT-Power simulation software. After model calibration based on measurements on a small size engine for two-wheel applications, the downsized version was compared to a larger power unit operated at constant engine speed for a scenario that featured up to 10 kW rated power.

Present work investigates both experimentally and numerically the benefits deriving from the use of split injections in increasing the engine power output and reducing the tendency to knock of a gasoline direct injection (GDI) engine. The here considered system is characterized by an optical access to the combustion chamber. Imaging in the UV-visible range is carried out by means of a high spatial and temporal resolution camera through an endoscopic system and a transparent window placed in the piston head. This last is modified to allow the view of the whole combustion chamber almost until the cylinder walls, to include the so-called eng-gas zones of the mixture, where undesired self-ignition may occur under some circumstances. Optical data are correlated to in-cylinder pressure oscillations on a cycle resolved basis.

The use of oxygenated and renewable fuels is nowadays a widespread means to reduce regulated pollutant emissions produced by internal combustion engines, as well as to reduce the greenhouse impact of transportation. Besides PM, NOx and HC emissions, also the size distribution of particles emitted at the engine exhaust represent meaningful information, considering its adverse effects on the environment and human health. In this work, the results of a comprehensive investigation on the combustion characteristics and the exhaust emissions of a GDI high performance engine, fuelled with pure bio-ethanol and European gasoline, are shown. The engine is a 4-cylinder, 4-stroke, 1750 cm₃ displacement, and turbocharged. The engine was operated at different speed/load conditions and two fuel injection strategies were investigated: homogeneous charge mode and stratified charge mode.