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The common realization of the necessity to reduce the use of mineral sources is promoting the use of alternative fuels. Big efforts are being made to replace petroleum derivatives in the internal combustion engines (ICEs). For this purpose it is mandatory to evaluate the behavior of non-conventional fuels in the ICEs. The optical diagnostics have proven to be a powerful tool to analyze the processes that take place inside the engine. In particular, 2d imaging in the infrared range can reveal new details about the effect of the fuel properties since this technique is still not very common. In this work, a comparison between commercial diesel fuel and two non-conventional fuels has been made in an optically accessible diesel engine. The non-conventional fuels are: the first generation biofuel Rapeseed Methyl Ester (RME) and an experimental blend of diesel and a fuel with high glycerol content (HG).

The occurrence of knock is the most limiting hindrance for modern Spark-Ignition (SI) engines. In order to understand its origin and move the operating condition as close as possible to onset of this potentially harmful phenomenon, a joint experimental and numerical investigation is the most recommended approach. A preliminary experimental activity was carried out at IM-CNR on a 0.4 liter GDI unit, equipped with a flat transparent piston. The analysis of flame front morphology allowed to correlate high levels of flame front wrinkling and negative curvature to knock prone operating conditions, such as increased spark timings or high levels of exhaust back-pressure. In this study a detailed CFD analysis is carried out for the same engine and operating point as the experiments. The aim of this activity is to deeper investigate the reasons behind the main outcomes of the experimental campaign.

Conventional fossil fuels are more and more regulated in terms of both engine-out emissions and fuel consumption. Moreover, oil price and political instabilities in oil-producer countries are pushing towards the use of alternative fuels compatible with the existing units. N-Butanol is an attractive candidate as conventional gasoline replacement, given its ease of production from bio-mass and key physico-chemical properties similar to their gasoline counterpart. A comparison in terms of combustion behavior of gasoline and n-Butanol is here presented by means of experiments and 3D-CFD simulations. The fuels are tested on a single-cylinder direct-injection spark-ignition (DISI) unit with an optically accessible flat piston. The analysis is carried out at stoichiometric undiluted condition and lean-diluted mixture for both pure fuels.

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.

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.

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.

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.

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 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.

In the present paper, infrared (IR) measurements were performed in order to study the development of injection and combustion in a transparent Euro 5 diesel engine operating in premixed mode. An elongated single-cylinder engine equipped with the multi-cylinder head of commercial passenger car and with common rail (CR) injection system, respectively, was used. A sapphire window was set in the bottom of the combustion chamber, and a sapphire ring was placed between the head and the top of the cylinder line. Measurements were carried out through both accesses by a new high-speed infrared (IR) digital imaging system obtaining information that was difficult to achieve by the conventional UV-visible camera. IR camera was able to detect the emitted light in the wavelength range 1.5-5 μm that is relevant for the emission bands of CO₂ and H₂O. The evaporation phase of pre and main injection, and subsequent combustion evolution were analyzed.

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.

Internal combustion engines are characterized by high pressure and thermal loads on pistons and in cylinders. The heat generated by the combustion process is dissipated by means of water and oil cooling systems. For the best design and optimization of the engine components it is necessary to know the components temperature in order to estimate the thermal flows. The purpose of this work is to measure the piston sapphire window temperature in a research optically accessible engine by combining two different techniques: measurements with templugs and with thermography. The method is very simple and can provide a reliable value of temperature within a small interval. It fits well for applications inside the engine because of its low technical level requirements. It consists of application of temperature sensitive stickers on the target component that makes it a very robust method, not affected by piston movement.

This study was conducted to determine the effects of the fouling process on the piezoelectric injectors in a transparent common-rail diesel engine. Piezoelectric injectors are characterized by a ceramic actuator that can dilate or retract when it receives a pulse of current. The piezo element controls a valve, which creates an imbalance in the pressure that is exerted at each end of the needle, causing the needle rising or closing. Two same model injectors were tested; one was new and the other one was fouled on a vehicle. The aim of the experimental investigation was to evaluate the performance of a new and a fouled piezoelectric injector in terms of injection and flame evolution. It was evaluated how the nozzle carbon deposits affect the injection quantity and combustion. The experimental apparatus was a single-cylinder research engine equipped with a Euro 5 multi-cylinder head. A second-generation common rail injection system and 6-hole piezoelectric injectors were used too.

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.

Blends of propane-diesel fuel can be used in direct injection diesel engines to improve the air-fuel mixing and the premixed combustion phase, and to reduce pollutant emissions. The potential benefits of usinf propane in diesel engines are both environmental and economic; furthermore, its use does not require changes to the compression ratio of conventional diesel engines. The present paper describes an experimental investigation of the injection process for different liquid preformed blends of propane-diesel fuel in an optically accessible Common Rail diesel engine. Slight modifications of the injection system were required in order to operate with a blend of propane-diesel fuel. Pure diesel fuel and two propane-diesel mixtures at different mass ratios were tested (20% and 40% in mass of propane named P20 and P40). First, injection in air at ambient temperature and atmospheric pressure were performed to verify the functionality of the modified Common Rail injection system.

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.