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In this doctoral thesis, diesel injection and spray formation in modern diesel engines were studied. The goal of this thesis is to answer some fundamental questions and hypotheses about injection and spray formation in modern diesel engines. First, the fundamental spray characteristics of renewable diesel were studied under non-evaporative conditions. Second, these spray characteristics were studied under extremely high cylinder pressure. Third, the spray characteristics of conical nozzle orifice geometry were studied. Finally, the spray characteristics of biofuel blends were studied in an optical engine during late-post-injection, which is relevant to exhaust gas after-treatment.Studies showed that the spray tip penetrations with renewable diesel and petroleum diesel were similar under non-evaporative conditions. The spray angle was slightly wider, spray tip velocities were higher, and the inner delay of the injector was shorter with renewable diesel. The conclusion of the study was that there is no need to redesign the combustion chamber or readjust the injection parameters due to wall impact or spray collision.Very high in-cylinder pressure and density have a significant effect on spray penetration. Higher gas phase mixing was observed with higher in-cylinder density. No negative aspects were found for extremely high gas density.When the spray tip penetration was compared between different conical geometries and a cylindrical nozzle orifice geometry, a clear difference was not found under non-evaporative conditions. This result is inconsistent with earlier studies. The main reasons for this inconsistency may be the different approach and high injection pressure. The spray angle was smaller, and the mass flow rate higher, with conical nozzle orifice geometry. Standard hydraulic flow measurement with an injection pressure of 100 bar underestimates the flow rate of conical orifices due to lack of cavitation.Different hypotheses about higher spray tip penetration and cylinder wall-wetting during late post-injection were studied. A clear difference in the spray tip penetration was not observed when three different fuel blends were compared. The conditions that would be needed for droplets to evaporate before reaching the cylinder wall are not attained with very late injection. Hence, hypotheses that the amount of fuel ending up on the cylinder walls is higher with biofuels are unlikely. The main reason for oil dilution rate differences between fuel blends is probably related to the volatility of the fuel fraction, or because the control unit increases the volume of the post-injections due to the lower volumetric heat value of renewable diesel.

We used a monoterpene volume mixing ratio dataset measured from 12 June 2006 to 24 September 2007 and from 1 June 2008 to 3 March 2009 at the SMEAR II station to quantify the magnitude of anthropogenic monoterpene emissions aside from biogenic origins, to examine the anthropogenic sources, and to look at other associated pollutants. We discuss the relations between increased monoterpene mixing ratios and particle concentrations. We also characterize chemical properties of aerosol particles during two monoterpene pollution episodes in case studies. Out of 580 days analyzed, anthropogenic monoterpene pollution episodes were found on 341 (58.8%) days. The average monoterpene mixing ratio increased from 0.19 to 0.26 ppbv due to the presence of anthropogenic monoterpenes, which is equal to an increase of 36.8%. The observed anthropogenic monoterpenes were mostly from the Korkeakoski sawmill. Other gas pollutants might occasionally be emitted during the episodes, but did not show clear association with anthropogenic monoterpenes. Aerosol particle concentrations substantially increased during episodes, and monoterpene mixing ratios showed strong connections with Aitken mode particles both in number and volume concentrations. Particles associated with monoterpene episodes reached a CCN (cloud concentration nucleus) size. The chemical characterizations of aerosol particles in case studies show that the increase in aerosol particle mass was mainly from secondary organic aerosol.