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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.

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.

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.

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.

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.

Quantitative measurements of the soot volume fraction and diameter performed by spectroscopic techniques within the combustion chamber of a diesel engine are employed to aid multidimensional simulation of the soot formation and oxidation processes. By changing the start of fuel injection, two different operating conditions are considered, which are characterized by different relative importance of the premixed to the diffusive stage of the combustion process. Both the reduced models by Hiroyasu et al., and the one by Nagle and Strikland- Constable are employed within the numerical simulation. The reason of the peculiar over-prediction of soot concentration of the latter model is discussed and related to the need of furnishing coherent values of the soot particle density and mean diameter.

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.