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In the modern GDI systems, the optimization of the fuel injection process is essential to prepare an air-fuel mixture capable to promote efficient combustion and reduce fuel consumption and pollutant emissions. A key feature for a better atomization is the fuel injection pressure. The increasing of the injection pressure is considered a good way for particle number (PN) reduction due to improved spray atomization, faster evaporation and better mixture formation. In this paper, a multi-hole GDI injector was tested to investigate the effects of very high injection pressures (IVHP), in addition to different ambient densities and temperatures, on the fuel spray morphology, in a cycle-resolved images analysis. Commercial gasoline was injected at the pressures ranging between 40.0 to 70.0 MPa, at gas densities varying between 1.12 to 11.5 kg/m3, and gas temperature up to 200°C.

It is well known that ethanol can be used in spark-ignition (SI) engines as a pure fuel or blended with gasoline. High enthalpy of vaporization of alcohols can affect air-fuel mixture formation prior to ignition and may form thicker liquid films around the intake valves, on the cylinder wall and piston crown. These liquid films can result in mixture non-homogeneities inside the combustion chamber and hence strongly influence the cyclic variability of early combustion stages. Starting from these considerations, the paper reports an experimental study of the initial phases of the combustion process in a single cylinder SI engine fueled with commercial gasoline and anhydrous ethanol, as well as their blend (50%vol alcohol). The engine was optically accessible and equipped with the cylinder head of a commercial power unit for two-wheel applications, with the same geometrical specifications (bore, stroke, compression ratio).

This paper reports the study of the effects of alternative diesel fuel and the impact for the air-fuel mixture preparation. The injection process characterization has been carried out in a non-evaporative high-density environment in order to measure the fuel injection rate and the spatial and temporal distribution of the fuel. The injection and vaporization processes have been characterized in an optically accessible single cylinder Common Rail diesel engine representing evaporative conditions similar to the real engine. The tests have been performed by means of a Bosch second generation common rail solenoid-driven fuel injection system with a 7-holes nozzle, flow number 440 cc/30s @100bar, 148deg cone opening angle (minisac type). Double injection strategy (pilot+main) has been implemented on the ECUs corresponding to operative running conditions of the commercial EURO 5 diesel engine.

The paper aims at performing an environmental and energetic optimization of a naturally aspirated, light-duty direct injection (DI) diesel engine, equipped with a Common Rail injection system. Injection modulation into up to three pulses is considered starting from an experimental campaign conducted under non-evaporative conditions in a quiescent optically-accessible cylindrical vessel containing nitrogen at different densities. The engine performances in terms of power and emitted NOx and soot are reproduced by multidimensional modelling of the in-cylinder processes. The radiated noise is evaluated by resorting to a recently developed methodology, based on the decomposition of the CFD 3D computed in-cylinder pressure signal. Once validated, both the CFD and the acoustic procedures are applied to the simulation of the prototype engine and are coupled to an external optimizer with the aim of minimizing fuel consumption, pollutant emissions and radiated noise.

The match among the increasing performance demands and the stringent requirements of emissions and the fuel consumption reduction needs a strong evolution in the two-wheel vehicle technology. In particular, many steps forward should be taken for the optimization of modern small motorcycles and scooters at low engine speeds and high loads. To this aim, detailed understanding of thermo-fluid dynamic phenomena that occur in the combustion chamber is fundamental. In this work, low-cost solutions are proposed to optimize ported fuel injection spark ignition (PFI SI) engines for two-wheel vehicles. The solutions are based on the change of phasing and on the splitting of the fuel injection in the intake manifold. The experimental activities were carried out in the combustion chamber of a single-cylinder 4-stroke optical engine fuelled with European commercial gasoline. The engine was equipped with a four-valve head of a commercial scooter engine.

High spatial and temporal resolution optical techniques were applied in a spark ignition (SI) engine in order to investigate the thermal and fluid dynamic phenomena occurring during the combustion process. The experiments were realized in the combustion chamber of an optically accessible single-cylinder port-fuel injection (PFI) SI engine. The engine was equipped with a four-valve head and with an external boost device. Two fuel injection strategies at closed-valve and open-valve occurring at wide open throttle were tested. Cycle-resolved digital imaging was used to follow the flame kernel growth and flame front propagation. Moreover, the effects of an abnormal combustion due to the firing of fuel deposition near the intake valves and on the piston surface were investigated. Natural emission spectroscopy in a wide wavelength range from ultraviolet to infrared was applied to detect the radical species that marked the combustion phenomena in the selected operating conditions.

In this work, a boosted single-cylinder spark ignition port-fuel injection optical engine was used for the experimental activity. Firstly, it was equipped with a four-valve head of a commercial turbocharged multi-cylinder engine. Then a prototype engine head with flush installed intake valves was tested. The effect of the different head geometry was evaluated in closed intake valves fuel injection condition. High spatial resolution cycle-resolved digital imaging was used to characterise the flame propagation. Moreover, the presence of diffusion-controlled flames near the valves and on the cylinder walls was investigated. These flames induced the formation of unburned hydrocarbons and soot particles. The spatial distribution and temporal evolution of soot were evaluated by the two colour pyrometry. The prototype configuration showed higher combustion process efficiency than the standard one inducing a little increase in performance and a slight reduction in carbon oxides emissions.

The flame front propagation in normal and abnormal combustion was investigated. Cycle-resolved flame emission imaging was applied in the combustion chamber of a port fuel injection boosted spark ignition engine. The engine was fuelled with a mixture of 90% iso-octane and 10% n-heptane by volume (PRF90). The effect of fuel injection phasing was studied. The combustion process was followed from the flame kernel formation until the opening of the exhaust valves. Different phenomena correlated to the abnormal combustion were analysed. Detailed information on ignition surfaces, end-gas auto-ignitions and knock were obtained. The appearance of autoignition centres in the end gas was evaluated in terms of timing, location and frequency of occurrence.

A satisfactory answer to the future severe normative on emissions and to the market request for spark ignition engines seems to be the use of downsized engines for passenger cars. Downsizing permits the increase in engines power and torque without the increase in cylinder capacity. The downsizing benefits are evident at part loads; on the other hand, more work should be done to optimize boosted engines at higher and full load. To this goal, a detailed knowledge of the thermo-fluid dynamic processes that occur in the combustion chamber is fundamental. The aim of this paper is the experimental investigation of the effect of the fuel injection in the intake manifold on the combustion process and pollutant formation in a boosted spark ignition (SI) engine. The experiments were performed on a partially transparent single-cylinder port fuel injection (PFI) SI engine, equipped with a four-valve head and boost device.

The growing demands on fuel economy and always stricter limitations on pollutant emissions has increased the interest in the ignition phenomena to guarantee successful flame development for all the spark ignition (SI) engine operating conditions. The initial size and the growth of the flame have a strong influence on the further development of the combustion process. In particular, for the new FIAT generation of turbocharged SI engines, the first times of spark ignition combustion are not yet fully understood. This is mainly due to the missing knowledge concerning the detailed physical and chemical processes taking place during the all set of the flame propagation. These processes often occur simultaneously, making difficult the interpretation of measurements. In the present paper, flame dynamic was followed by UV-visible emission imaging in an optical SI engine.

Aim of this work is to develop a general purpose model for combustion and knocking prediction in SI engines, by coupling a thermo-fluid dynamic model for engine simulation with a general detailed kinetic scheme, including the low-temperature oxidation mechanism, for the prediction of the auto-ignition behavior of hydrocarbons. A quasi-D approach is used to describe the in-cylinder thermodynamic processes, applying the conservation of mass and energy over the cylinder volume, modeled as a single open system. The complex chemistry model has been embedded into the code, by using the same integration algorithm for the conservation equations and the reacting species, and taking into account their mutual interaction in the energy balance. A flame area evolution predictive approach is used to evaluate the turbulent flame front propagation as function of the engine operating parameters.

Two different optical techniques for detection, sizing and counting nanoparticles were applied to undiluted exhaust from 16 v–1900 cc Common Rail diesel engine upstream and downstream a Catalyzed Diesel Particulate Filter (CDPF): Broadband Ultraviolet–Visible Extinction and Scattering Spectroscopy (BUVESS) and Laser Induced Incandescence (LII). They are powerful “in situ” and non-intrusive techniques; they are able to measure mass concentration and size of particles, considering their chemical properties. BUVESS overcomes the intrinsic limitations of single wavelength techniques because it takes advantage of data at several wavelengths to retrieve primary particle size distribution. LII measures mean size of primary particles with a large dynamic range, not limited by aggregate size and by complex retrieving procedure.

Actual emission legislation limits strongly the amount of pollutant in the atmosphere from internal combustion engine. In particular diesel engines widely emit NOx and particulate matter (PM). The last one has principally a carbonaceous nature and presents micronic and submicronic particles extremely dangerous for human health since it could deposit in the lung. In this work, a technique based on broadband ultraviolet (UV) visible scattering and extinction is applied inside a transparent DI CR diesel engine in order to analyze the soot evolution and oxidation. The study is carried out with particular detail for different injection strategies characterized of two and three injections per cycle, Pre+Main and Pre+Main+Post, considering the late combustion before the exhaust stroke. The analysis is performed in terms of size, mass concentration, and chemical and physical nature.

The aim of the paper is the characterization in terms of chemical and physical nature of particles at exhaust of spark ignition (SI) engine. Measurements were carried out at exhaust of 16v - 1.2 litre Port Fuel Injection Spark Ignition engine downstream a catalyst. The emission of nanoparticles was investigated by optical techniques and conventional methods. In particular laser induced incandescence (LII), and broadband multiwavelength extinction-scattering spectroscopy (BUVESS) were used. LII allowed the detection and sizing primary particles of carbonaceous nature. BUVESS measured particle size distribution by numerical procedure that took advantage by data at several wavelengths. The optical results were compared with those obtained by conventional methods like opacimeter for mass concentration and Electrical Low Pressure Impactor (ELPI) for sizing. Different engine operating conditions were selected in order to evaluate their influence on the particle nature and size distribution.

This paper illustrates the results of an experimental investigation on the liquid fuel spray from a multi-jet common rail injection system both under non evaporative and evaporative conditions. Tests have been taken using a 5 hole, 0.13 mm diameter, 150° spray angle, micro-sac nozzle having a flow rate of 270 cm3/30 sec@10 MPa exploring different injection strategies. Experiments have been taken, under non evaporative conditions, injecting the fuel within stagnant inert gas, at different density, in a high-pressure optically-accessible cylindrical vessel with three large quartz windows. Under evaporative conditions, the experiments have been taken within a crank-case scavenged single-cylinder 2-stroke direct injection Diesel engine provided of optical accesses to the combustion chamber. It allows to study the fuel injection process under thermodynamic conditions similar to those currently reached in modern direct injection diesel engines.

The intention of the presented work was to develop a new simulation tool that fits into a CFD (computational fluid dynamics) workflow and provides information about the soot particle size distribution. Additionally it was necessary to improve and use state-of-the-art measurement techniques in order to be able to gain more knowledge about the behavior of the soot particles and to validate the achieved simulation results. The work has been done as a joint research financed by the European Community under FP5.

One of the most important phases in the development of direct-injected diesel engines is the optimization of the fuel spray evolution within the combustion chamber, since it strongly influences both the engine performance and the pollutant emissions. Aim of the present paper is to provide information about mixture formation within the combustion chamber of a heavy-duty direct injection (HDDI) diesel engine for marine applications. Spray evolution, in terms of tip penetration, is at first investigated under quiescent conditions, both experimentally and numerically, injecting the fuel in a vessel under ambient temperature and controlled gas back-pressure. Results of penetration and images of the spray from the optically accessible high-pressure vessel are used to investigate the capabilities of some state-of-the-art spray models within the STAR-CD software in correctly capturing spray shape and propagation.

The paper describes the results of a parallel 1D thermo-fluid dynamic simulation and experimental investigation of a DI turbocharged Diesel engine. The attention has been focused on the overall engine performances (air flow, torque, power, fuel consumption) as well as on the emissions (NO and particulate) along the after-treatment system, which presents a particulate filter. The 1D research code GASDYN for the simulation of the whole engine system has been enhanced by the introduction of a multi-zone quasi-dimensional combustion model for direct injection Diesel engines. The effect of multiple injections is taken into account (pilot and main injection). The prediction of NO and soot has been carried out respectively by means of a super-extended Zeldovich mechanism and by the Hiroyasu kinetic approach.

This paper illustrates the results of an experimental characterization of a high pressure diesel spray injected by a common rail (CR) injection system both under non-evaporative and evaporative conditions. Tests have been made injecting the fuel with a single hole injector having a diameter of 0.18 mm with L/D=5.56. The fuel has been sprayed at 60, 90 and 120 MPa, with an ambient pressure ranging between 1.2 to 5.0 MPa. The spray evolution has been investigated, by the Mie scattering technique, illuminating the fuel jet and acquiring single shot images by a CCD camera. Tests under non-evaporative conditions have been carried out in an optically accessible high pressure vessel filled with inert gas (N2) at diesel-like density conditions. The instantaneous fuel injection rate, obtained with a time resolution of 10 microseconds, has been also evaluated by an AVL Fuel Meter working on the Bosch Tube principle.

The DEXA Cluster consisted of three closely interlinked projects. In 2003 the DEXA Cluster concluded by demonstrating the successful development of critical technologies for Diesel exhaust particulate after-treatment, without adverse effects on NOx emissions and maintaining the fuel economy advantages of the Diesel engine well beyond the EURO IV (2000) emission standards horizon. In the present paper the most important results of the DEXA Cluster projects in the demonstration of advanced particulate control technologies, the development of a simulation toolkit for the design of diesel exhaust after-treatment systems and the development of novel particulate characterization methodologies, are presented. The motivation for the DEXA Cluster research was to increase the market competitiveness of diesel engine powertrains for passenger cars worldwide, and to accelerate the adoption of particulate control technology.