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Nanoparticles characterisation at the spark ignition engine exhaust

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

Journal of KONES

2008

Vol. 15, No. 3

347-355

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.

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

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

Silniki Spalinowe

2007

R. 46, nr SC3

206-217

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.