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Pure sunflower oil was used in a Perkins 4-236 DI diesel engine at 2200 rpm and maximum power, particulate samples at 50°C were obtained from the exhaust 7m from the exhaust port in an air cooled exhaust pipe. The engine lubricating oil was fresh and contained no fuel contamination. The sunflower oil had higher particulate, UHC, CO and NOx emissions than for diesel. This was attributed to the shorter ignition delay and higher diffusive burning. The higher UHC emissions also resulted in a higher particulate SOF. Sunflower oil contained no fuel PAH above 1 ppm and there was no source of PAH from the lubricating oil. However, significant PAH emissions were found in the particulate SOF, but at a level well below that for diesel. It was shown that the bulk of this PAH could be attributed to the thermal desorption of PAH from the exhaust pipe walls. Hence, there was little PAH generated by pyrosynthesis as part of the combustion process.

A small 0.220 litre Petter IDI single cylinder engine was investigated over a 120 hour test period, consisting of 40 three hour test runs, with emission measurements and lubricating oil analysis every 20 hours for the same batch of fuel and lubrication oil. The particulates were analysed for the SOF and for the fuel/lubricant proportion using TGA. Fuel dilution of the lubricating oil was shown to increase uniformly with time and reached 10% after 120 hours, there was an associated decrease in the viscosity and increase in the lube oil fraction in the particulate SOF. Carbon contamination of the lubricating oil increased to 1.6% by mass over the 120 hour test period. The particulate emissions decreased initially and then increased after 50 hours, but the effect was no more than a 30% variation, mainly caused by variations in the carbon emissions. The motoring particulates were found to be low and dominated by vaporised lubricating oil.

Diesel engine exhaust pipe and incylinder deposits were analysed for the global fuel, lube oil, carbon and ash fractions for a range of diesel engines. A large SOF fraction, typically 30%, was found and this was dominated by lubricating oil. These deposits are shown to contain significant levels of PAH and hence provide a source of diesel PAH emissions and possible sites for incylinder pyrosynthesis of high molecular weight PAH. A Perkins 4-236 NA DI was used to investigate the role of exhaust pipe deposits on PAH emissions. It was shown that PAH compounds could be volatilised from the exhaust pipe. The difference in the exhaust inlet and outlet particulate composition for diesel and kerosene fuels was used to quantify the n-alkane and PAH emissions originating from the exhaust pipe deposits. Comparison with pure PAH free fuels showed that the exhaust outlet PAH composition was similar to that expected from the exhaust pipe deposits.

N-hexadecane, kerosene and diesel fuels were used for powering a new IDI diesel engine in order to elucidate the role of in-cylinder pyrosynthesis of PAH in diesel emissions. The present work is a complementary to previous investigations (1,2,3) where exhaust deposits have contributed to and interfered with the results. This was eliminated by using a brand new deposit-free engine. Nonetheless, high levels of PAH were detected in the exhaust even with the PAH free fuels. This was attributable to the high rates of lube oil consumption during the running-in period of this engine. The fuel PAH were also shown to play a significant role in the total emissions of these species in diesel combustion.

An old single cylinder Petter AA1 and a new four cylinder Ford 1.61 engines were operated over a wide range of steady state conditions using kerosene and diesel fuels. The two engines exhibited different trends in forming the particulate emissions. For both fuels the particulate emissions were dominated by the carbon for the old engine, and by the SOF for the new engine where the latter was characterized by its low level of emissions. The engine operating conditions also influenced the emissions of the different particulate fractions. Generally, the old engine had higher unburnt lube oil emissions as well as high survival of diesel n-alkanes and PAH in the emissions. However, in the case of kerosene and the new engine when operated both with kerosene and diesel fuel, the pyrosynthesis of these compounds was evident. Sulphates in the particulates, which originated mainly in the fuel, were shown to incorporate low levels of background from the engine deposits and the lubricating oil.

The objective was to investigate PAH emissions in diesel particulates using a kerosene fuel that had a PAH content that was predominantly two ring. Higher PAH were two orders of magnitude lower in concentration in the fuel than for diesel, but the two ring PAH were a higher proportion of the fuel than for diesel. Pyrosynthesis of higher PAH in the particulate from the two ring PAH would thus be easier to detect for kerosene. Fresh PAH free lubricating oil was used throughout in an attempt to eliminate additional sources of PAH. The kerosene results showed that emissions of higher PAH were an order of magnitude lower than with diesel. However, these PAH emissions were compatible with an unburnt fuel source, as the n-alkane results showed that the higher MW fuel components had a much greater survivablity than for diesel. A contribution to PAH and n-alkane emissions from the exhaust pipe deposits was also identified.