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This paper reports the results of an experimental investigation on the combustion characteristics and exhaust particulate emissions of a GDI high performance engine, fuelled with blends of bio-ethanol and European gasoline fuel. The engine is a 4-cylinder, 4-stroke, 1750 cm₃ displacement, and turbocharged. The engine was operated at fixed speed and load, namely 1500 rpm and 110 Nm, and fuelled with gasoline (E0), ethanol (E100) and two blends 50% v/v (E50) and 85% v/v (E85) of ethanol in gasoline. Two fuel injection strategies were investigated: homogeneous charge and stratified charge combustion mode. The study mainly focuses on the effects of fuel injection strategy and ethanol upon the emissions of particulate matter (PM), in terms of mass, number concentration and size distribution.

The paper investigates the idle operating condition of a current production turbocharged Gasoline Direct Injected (GDI) high performance engine both from an experimental and a numerical perspective. Due to the low engine speed, to the low injection pressure and to the null contribution of the turbocharger, the engine condition is far from the standard points of investigation. According to the low heat flux due to combustion, temperature levels are low and reduced fuel evaporation is expected. Consequently, fuel spray evolution within the combustion chamber and spray/wall interaction are key points for the understanding of the combustion process. In order to properly investigate and understand the many complex phenomena, a wide set of engine speeds was experimentally investigated and, as far as the understanding of the physics of spray/wall interaction is concerned, many different injection strategies are tested.

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 aim of this paper is the experimental investigation of the effect of direct fuel injection on the combustion process and pollutant formation in a spark ignition (SI) two-wheel engine. The engine is a 250cc single cylinder, four-stroke spark-ignition firstly equipped with a four-valve PFI head and then with GDI one operating with European commercial gasoline and Bio-ethanol. It is equipped with a wide sapphire window in the bottom of the chamber and quartz cylinder. In the combustion chamber, optical techniques based on 2D-digital imaging were used to follow the injection and flame propagation and spectroscopic measurements were carried out in order to evaluate the main radical species. Radical species such as OH and CH were detected and used to follow the chemical phenomena related to the fuel quality. Measurements were carried out at different engine speeds and combustion strategies based on different injection pressures.

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.

Nowadays an elevated number of two, three and four wheels vehicles circulating in the world-wide urban areas is equipped with Port Fuel Injection Spark Ignition (PFI SI) engines. Their technological level is high, but a further optimization is still possible, especially at low engine speed and high load. To this purpose, the scientific community is now focused on deepening the understanding of thermo fluid dynamic phenomena that takes place in this kind of engine: the final purpose is to find key points for the reduction in engine specific fuel consumption and exhaust emissions without a decrease in performance. In this work, the combustion process was investigated in an optically accessible single cylinder PFI SI engine. It was equipped with the head, injection device and exhaust line of a commercial small engine for two-wheel vehicles, it had the same geometrical characteristics in terms of bore, stroke and compression ratio.

The small engine for two-wheel vehicles has generally high possibility to be optimized at low speeds and high loads. In these conditions fuel consumption and pollutants emission should be reduced maintaining the performance levels. This optimization can be realized only improving the basic knowledge of the thermo-fluid dynamic phenomena occurring during the combustion process. It is known that, during the fuel injection phase in PFI SI engines, thin films of liquid fuel can form on the valves surface and on the cylinder walls. Successively the fuel films interact with the intake manifold and the combustion chamber gas flow. During the normal combustion process, it is possible to achieve gas temperature and mixture strength conditions that lead to fuel film ignition. This phenomenon can create diffusion-controlled flames that can persist well after the normal combustion event. These flames induce the emission of soot and unburned hydrocarbons.

The match between the increasing performance demands and stringent requirements of emissions and fuel consumption reduction needs a strong evolution in the 2-wheel vehicle technology. In particular many steps forward should be taken for the optimization of modern small motorcycle and scooter at low engine speeds and low temperature start. To this aim, the detailed understandings of thermal and fluid-dynamic phenomena that occur in the combustion chamber are fundamental. In this work, experimental activities were realized in the combustion chamber of a single-cylinder 4-stroke optical engine. The engine was equipped with a four-valve head of a commercial scooter engine. High spatial resolution imaging was used to follow the flame kernel growth and flame front propagation. Moreover, the effects of an abnormal combustion due to firing of fuel deposition near the intake valves and on the piston surface were investigated.

This paper reports on the analysis of flame kinematics and cycle variation in port fuel injection (PFI) spark ignition (SI) engine. The engine was equipped with a four-valve head and with an external boost device. Different operating conditions were considered. Cycle-resolved digital imaging was used to investigate flame motion and the effects of an abnormal combustion due to the firing of fuel deposition near the intake valves and on the piston surface. Various algorithms are applied to the acquired images. Coefficients of Proper Orthogonal Decomposition (POD) were computed and used for a statistical analysis of cycle variability. The advantage is that the analysis can be run on a small number of scalar coefficients rather than on the full data set of pixel valued luminosity.