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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.

Pollutant emission of vehicle cars is nowadays a fundamental aspect to take into account. In the last decays, the company have been forced to study new solutions, such as alternative fuel and learn burn mixture strategy, to reduce the vehicle’s pollutants below the limits imposed by emission regulations. Pre-chamber ignition system presents potential reductions in emission levels and fuel consumption, operating with lean burn mixtures and alternative fuels. As alternative fuels, methane is considered one of the most interesting. It has wider flammable limits and better anti-knock properties than gasoline. Moreover, it is characterized by lower CO2 emissions. The aim of this work is to study the evolution of the plasma jets in a different in-cylinder conditions. The activity was carried out in a research optical small spark ignition engine equipped alternatively with standard ignition system and per-chamber.

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.

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.

Fuel depletion as well as the growing concerns on environmental issues prompt to the use of more eco-friendly fuels. The compressed natural gas (CNG) is considered one of the most promising alternative fuel for engine applications because of the lower emissions. Nevertheless, recent studies highlighted the presence of ultrafine particle emissions at the exhaust of CNG engines. The present study aims to investigate the effect of CNG on particle formation and emissions when it was direct injected and when it was dual fueled with gasoline. In this latter case, the CNG was direct injected and the gasoline port fuel injected. The study was carried out on a transparent single cylinder SI engine in order to investigate the in-cylinder process by real time non-intrusive diagnostics. In-cylinder 2D chemiluminescence measurements from UV to visible were carried out.

In the urban area the internal combustion engines are the main source of CO₂, NO and particulate matter (PM) emissions. The reduction of these emissions is no more an option, but a necessity highlighted by the even stricter emission standards. In the last years, even more attention was paid to the alternative fuels. They allow both reducing the fuel consumption and the pollutant emissions. With regards to the gaseous fuels, methane is considered one of the most interesting in terms of engine application. It represents an immediate advantage over other hydrocarbon fuels because of the lower C/H ratio. In this paper the effect of the methane on the combustion process, the pollutant emissions and the engine performance was analyzed. The measurements were carried out in an optically accessible single-cylinder, Port Fuel Injection, four-stroke SI engine equipped with the cylinder head of a commercial 250 cc motorcycles engine and fuelled both with gasoline and methane.

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.

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.

With a view to reducing the environmental impact of fossil fuels, advanced lignin-based biofuels could provide a valuable contribute, since lignin is the most abundant biopolymer on earth after cellulose. However, its thermophysical properties would hamper its use as a pure fuel. In this work we investigated the combustion behavior of sprays of a liquid lignin-methanol blend and evaluated its potential as a low-carbon marine fuel for large two-stroke engines. To this end, an experimental campaign was conducted in an optically accessible combustion chamber whose main dimensions correspond to those of a single cylinder for large two-stroke engines. The chamber is provided with optical accesses for optical diagnostics of the combustion process. The combustion of the mixture was ignited using a diesel pilot jet as the ignition source. Two marine injectors are mounted in the chamber, namely “main” and “pilot” injectors.

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.

This paper aims to correlate the in-cylinder soot formation and the exhaust particle emissions for different methods of gasoline/ethanol fueling in spark ignition engine. In particular, the engine was fueled with gasoline and ethanol separately and not, in this latter case both blended (E30) and dual fueled (EDF). For E30 the bend was direct injected and for EDF, the ethanol was injected in the combustion chamber and the gasoline into the intake duct. For both the injection configurations, the same percentage of ethanol in gasoline was supplied: 30%v/v. The measurements were carried out at 2000 and 4000 rpm, under full load, and stoichiometric condition, in small single cylinder optical engine. 2D-digital imaging was performed to follow the combustion process with a high spatial and temporal resolution through a full-bore optical piston. The two-color pyrometry was applied for the analysis of the in cylinder soot formation in the combustion chamber.

With the aim of decarbonizing the vehicles fleet, the use of hydrogen is promising solution. Hydrogen is an energy carrier, carbon-free, with high calorific value and with no CO2 and HC emissions burning in ICE. Hydrogen use in spark ignition engines has already been extensively investigated and optimized. On the other hand, its use in compression ignition engines has been little developed and, therefore, there is a lack of information regarding the combustion in ultra-lean conditions, typical of diesel engines. Several applications employ dual fuel combustion for the easy management of the PFI injection system to be applied in addition to the DI Common Rail system. However, this mode suffers from several problems regarding the management of the maximum flow rate of hydrogen into the intake. In particular, to avoid throwing hydrogen into the exhaust, injection must be started after the valve crossing.

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 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.

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.

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.

Recent needs of reducing pollutant emissions of internal combustion engines have pushed the development of non-conventional ignition systems. One of the most promising techniques appears to be the so-called pre-chamber turbulent jet ignition combustion system in which a jet of hot combusting gases is employed to initiate the combustion in the main chamber. In the present study, the combustion process related to this ignition system has been experimentally investigated in an optically accessible single cylinder spark-ignition engine. The pre-chamber was composed of a gas injector and a spark-plug, embedded in a small annular chamber connected to the cylinder through a four-hole pipette. A small amount of methane is injected within the pre-chamber for initiating the combustion. The flame reaches the combustion chamber through four narrow orifices and rapidly consumes a homogeneous mixture of port injected methane and air.

The constant aim of the automotive industry is the further improvement of engine efficiency and the simultaneous reduction of the exhaust emissions. In order to optimize the internal combustion engines it is necessary to further improve the basic knowledge of the thermo-fluid dynamic phenomena occurring during the combustion process. In this context, the application of optical diagnostic techniques permits a deep insight into the fundamental processes such as flow development, fuel injection, and combustion process. In this paper the analysis of the combustion process of gaseous fuel ignited by the plasma jets coming from a prechamber was performed. The investigation was carried out in an optically accessible small Direct Injection Spark-Ignition (DI SI) engine fueled with Methane. The ignition was obtained with a properly designed fueled prechamber prototype.

This paper investigates abnormal combustion during the cranking phase of spark-ignition small engines, specifically the occurrence of backfire at the release of the starter motor during kickback. The research focusses on the influence of fuel composition, mainly in terms of ethanol percentage, on backfire occurrence. Interest in this abnormal combustion is growing due to the increased use of fuels with different chemical-physical properties with respect to gasoline. Moreover, this issue will become even more topical due to the implementation of simple control and fuel supply systems on low cost-engines, which are widely used in developing countries. Experimentation was carried out in an optically accessible engine derived from a 4-stroke spark ignition engine for two-wheel vehicles. The test bench was instrumented and adapted in order to simulate the engine conditions that lead to anomalous ignition in the intake duct (backfire) during the reverse rotation of the engine (kickback).

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.