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1

Optical diagnostics in a spark ignition engine for two-wheel vehicles

100%

Merola S. S. , Sementa P. , Tornatore C.

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tom Vol. 17, No. 4

323-336

EN

Different optical techniques were applied to describe the thermal and chemical processes that occur in a SI small engine from the ported fuel injection and in-cylinder mixture formation to the combustion process and the exhaust emission. In PFI SI engines, the atomized fuel is sprayed towards the intake valves, where it may evaporate, puddle or rebound. Furthermore, a portion of the fuel may flow directly into the cylinder or impinge upon the port walls. These phenomena occur in varying degrees and depend upon the engine design, injector location and engine operation. Potentially the fuel can enter the cylinder in a poorly atomized state, leading to an increased unburned hydrocarbon emissions. This is particularly true during cold operation, when evaporation is low. In the small-motorcycle and scooter engines the fuel injection occurs in smaller intake manifold than light-duty vehicle engines, increasing the criticism of the fuel-wall interaction. The experimental investigations were performed in a single cylinder engine constituted by an elongated optically accessible piston and equipped with the head and injection system of a reference 4-stroke engine for small vehicles. High spatial resolution imaging was used to characterize the fuel injection phase. The cycle resolved visualization was performed to follow the flame propagation from the intake spark ignition to the exhaust phase. Natural emission spectroscopy measurements were applied in the ultraviolet-visible wavelength range to identify the chemical species that are markers of the combustion process and to follow the formation of pollutants.

2

In - cylinder OH and CO2* detection in SI engine through UV natural emission spectroscopy

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Merola S. S. , Tornatore C. , Marchitto L. , Valentino G.

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tom Vol. 19, No. 4

429-437

EN

Processes of the combustion of liquid fuels and solid are more complex than combustion of fuel gases. With reference to liquid fuels occur additionally processes of vaporization of the fuel, and with reference to solid fuels - decomposition of the solid phase with processes of melting and vaporization, pyrolysis, or gasification. This simultaneous and also different influence of different parameters is sometimes a reason of incorrect interpretation of experimental results. The study of the theoretical model of the combustion process concerning of liquid and solid fuels and which then the model takes into account also the gas- phase, because combustion processes take place in this phase, and occurs the interaction of the phase gas- and liquid or the solid one. The theoretical model is presented basing on experimental initial researches realized in a model with reference to liquid fuels and solid ones. Researches realized in the constant volume chamber with measurements of the pressure during the process of the combustion with the use of quick photography and with measurement of the distribution of the velocity in the spray of the fuel and droplet measurements by means the laser Doppler equipment LDV and PDPA. There were obtained a good agreement of findings experimental researches with the theoretical model. Generally, on the combustion velocity of liquid fuels and solid one significant influence has a kind (laminar, temporary and turbulent) and the thickness of the thermal boundary layer.

3

Effect of EGR on nanoprticles at Common-rail diesel engines exhaust

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Merola S. S. , Tornatore C. , Vaglieco B. M.

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tom R. 46, nr SC3

206-217

EN

In the last years, diesel emission control strategies based on engine design and after-treatment devices, have been very successful in the reduction of the total particulate mass and gaseous emissions. Nevertheless they have been significantly less effective in reducing the total number of particles. Thus, when EURO 5 will be introduced, it will be difficult to meet the emission standards with the present technologies. Nowadays diesel engines are equipped with the Exhaust Gas Recirculation (EGR) system that allows the reduction of thermal-Nitrogen Oxides but it could also influence particles emissions. For this reason, the aim of the present work is to evaluate the effect of EGR on the balance between the primary particles and the aggregates at the exhaust of diesel engines. The idea is to find out a relation between EGR percentage and the size of the emitted particles for every speed and load. Two different methodologies for detection, sizing and counting nanoparticles were used. Electrical Low Pressure Impactor (ELPI) measured the particle size distributions in the range 7 nm-10 μm, without distinction between primary particles and aggregates. Laser Induced Incandescence (LII) allowed to determine soot primary particles diameter. ELPI measurements pointed out the increasing of number concentration and size of particles with the EGR. The size distributions showed a maximum in the range of 54-91nm with negligible number of particles larger than 300 nm. For alt the conditions, an increase of number concentration of particles bigger than 54 nm and a reduction of smaller ones was measured. This was due to the agglomeration effect caused by the reintroduction of particles contained in the exhaust gases into the cylinder during the EGR. LII measurements showed that at fixed engine speed and for alt EGR values, the diameters of primary particles increased with engine load. Moreover smaller primary particles were formed at higher speed. With respect to EGR variation, for every condition the primary particles diameters increased due to the partial oxidation of soot recirculated in the combustion chamber ad the successive superficial growth. Taking into account the proposed results, for each engine operating condition, the best EGR value could be chosen taking into account the size distribution of the produced particles and not only the NOx-soot trade-off.

4

Nanoparticles characterisation at the spark ignition engine exhaust

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Merola S. S. , Tornatore C. , Vaglieco B. M.

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tom Vol. 15, No. 3

347-355

EN

The particles at the exhaust of two Port Fuel Injection Spark Ignition (PFI-SI) engines were characterised in terms of number size distribution and chemical properties. Optical techniques based on the Laser Induced Incandescence (LII) and on the Broadband Ultraviolet - Visible Extinction and Scattering Spectroscopy (BUVESS) were applied. The optical results were compared with those obtained by Electrical Low Pressure Impactor (ELPI). The aim of the work was the characterisation of the nanoparticles emitted by Port Fuel Injection Spark Ignition (PFI - SI) engines in terms of number size distribution and chemical-physical properties. Two PFI - SI engines were used for the experiments: a four-cylinder engine and a research optically accessible single cylinder engine. The experiments were performed at the exhaust of a multi-cylinder SI engine equipped with a three way catalyst (TWC) and in the combustion chamber and at the exhaust of a single-cylinder optical engine. High number concentrations of nanoparticles (D less than 50 nm) were detected. The presence of carbonaceous particles at the exhausts was due to the ignition of the fuel film deposits on the intake valves and on the cylinder walls. This was demonstrated by the optical measurements performed in the combustion chamber of the research engine. Different engine operating conditions were considered.

5

Optical diagnostics of the cyclic variation in the kernel development and abnormal combustion: SI boosted engine

88%

Gallardo-Ruiz J. M. , Ballais R. , Merola S. S. , Sementa P. , Tornatore C.

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tom Vol. 17, No. 2

103-111

EN

The combustion stability of a spark ignition engine significantly influences its performances. The cyclic variation is generally evaluated by the fluctuation of in-cylinder peak pressure which changes in both magnitude and position measured from TDC. In this work the cyclic variation of combustion process were analysed as function of crank angles. The different SI engine process phases were investigated. The pressure related data were correlated with cycle resolved visualization measurements. The cycle resolved digital imaging was applied to follow the kernel inception and growth and to study the flame front propagation until the exhaust phase. A custom numerical post-detection procedure was applied to correlate the optical data from the integral luminous signal measured in the combustion chamber with the pressure related parameters .The flame kernel and the abnormal combustion due to the fuel deposits burning resulted particular relevant for the cycle-to-cycle variations. Optical measurements outlined better than pressure related analysis the role of the early andfinal stages of the combustion process. The experiments were performed in a 400 cm3 single cylinder, port fuel injection, four-stroke spark ignition engine. The engine was optical accessible with the same geometrical parameters as a 1600 cm3 passenger car engine. The head and the injection system of a commercial engine mounted on a passenger car were used. Standard EURO IV gasoline was used

6

Optical diagnostics of the cycle-to-cycle variation in the kernel development and abnormal combustion: SI small engine

88%

Ballais , Gallardo-Ruiz J. M. , Merola S. S. , Sementa P. , Tornatore C.

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tom Vol. 17, No. 2

17-25

EN

The combustion stability and more in details the cyclic variability significantly influences the performance and the pollutant emissions of a spark ignition engine. In this work, an experimental research activity was carried out to investigate the influence of the different combustion phases on the cycle-to-cycle variation. In particular the flame kernel development and the fuel deposits burning were investigated by in-cylinder pressure measurements and optical investigations. Engine cycle resolved visualization was applied to characterize the spatial evolution of the flame front from the spark ignition until the exhaust phase. A numerical custom post-detection procedure was used to correlate the optical data with the pressure related parameters during the combustion process. The simultaneous use of optical diagnostics and pressure related analysis demonstrated the fundamental role of the first stage and late phase of the combustion on the spark ignition engine process. Flame kernel and diffusion controlled flame due to fuel deposits burning dominated the cyclic variability of in-cylinder combustion. The experiments were realized in a 250 cm3 single cylinder, port fuel injection, four-stroke spark ignition engine. The engine was optically accessible and it was equipped with the head, injection system and exhaust device of a commercial engine mounted on small motorcycles and scooters. Standard EURO IVgasoline was used.

7

Valorization of n-butanol as gasoline replacement in a DISI engine and the effect of injection phasing

88%

Merola S. S. , Irimescu A. , Valentino G. , Colmenares-Quintero R. F. , Rodas Y. A. L.

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tom nr 204

169--185

EN

Alcohols represent a viable replacement for gasoline> with the advantages of providing improved energy security as well as reduced environmental impact. Compared to ethanol, which holds the majority of the alternative fuels market share in transportation, n-butanol features higher energy density and better compatibility with existing fuel systems designed for gasoline. Given this background, the present study investigated the use of pure n-butanol fuelling of a wall guided direct injection spark ignition (DISI) engine with optical accessibility through the piston crown. Different injection timings were considered, and variations of soot emissions were evaluated based on smoke measurements. Besides thermodynamic investigations through the analysis in-cylinder pressure traces, flame chemiluminescence was applied for a more detailed view of the chemical processes during combustion. All conditions were benchmarked to gasoline fuelling, thus giving comprehensive information on the effect of fuel properties. It was found that the change in injection timing, even by a relatively reduced crank angle, had a significant effect on the smoke at the exhaust, for both fuel types. Early fuel delivery resulted in high soot emissions, while late injection had the opposite effect. No soot- nitrogen oxides trade-off point, specific for diesel power units, could be identified, but the optimum injection strategy resulted in high engine output and low particulate emissions. The alcohol featured increased sensitivity not only to changes in the start of injection, but also showed the potential for very low smoke. The investigations further emphasize the importance of air-fuel mixture formation and also identified ways to minimize the environmental impact of DISI engines through the development of optimized control strategies.