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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.

The influence of nozzle sac volume on the composition of the fuel derived solvent organic fraction of diesel particulate from a naturally aspirated 1 litre per cylinder diesel engine was studied. Significant differences in the quantities of the polycyclic aromatic compounds for different sac volumes were found. The emission differences were due to the reduction of unburnt fuel contributions to particulate SOF as the sac volume was reduced.

A naturally aspirated Perkins 4-236 engine was compared with a similar turbocharged Perkins engine. The higher pressures and temperature of a turbocharged engine should make the pyrosynthesis of PAH more likely than for a NA engine and this was investigated using the fuel n-alkanes as tracers for the unburnt fuel of the same fuel distillation fraction as the PAH. The results showed that the below C20 the NA and TC survivabilities of fuel n-alkanes onto the particulates were similar at below 0.02%. For higher n-alkanes the turbocharger was much more efficient at burning the fuel, with survivabilities of C24 a factor of 10 below the NA results. The higher operating temperatures of the TC engine reduced the UHC emissions and this reduced the higher boiling fraction unburned fuel. In contrast to these results the fuel PAH apparent survivability's were higher, by approximately a factor of 10, for the turbocharged engine for equivalent boiling point compounds in the range C18-C22.

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.

Exhaust particulate and gas composition samples were obtained at various distances along an externally air cooled exhaust from a Perkins 4-236 single cylinder engine. The change in the particulate composition was determined as a function of the exhaust distance and local temperature. Exhaust temperatures were in the range 200 - 260C at entry to the tunnel at all engine conditions. A constant filter paper and sample temperature of 50C was used for both exhaust and dilution tunnel samples and the filter paper was mounted in an oven for this purpose and the particulate sample was tranported through heated lines to this oven. Associated with these particulate measurements were gas analysis measurements. UHC were measured at 180, 50 and 2C in the exhaust and the differences were taken as an indication of the condensable hydrocarbons over that temperature difference.

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.

The relationship between Diesel fuel composition and that of the solvent organic fraction of Diesel particulates; was investigated for an old DI Petter engine and a current technology DI Perkins engine. Polynuclear aromatic compounds (PAC) were indentified using high resolution capillary column chromatography with a parallel triple detector system for polycyclic aromatic hydrocarbons (PAH), nitrogen containing PAH (PANH) and sulphur containing PAH (PASH). The Perkins engine gave emissions with much lower unburnt hydrocarbons than the Petter engine and this was shown to be due mainly to the much greater efficiency of burn out of low molecular weight fuel compounds including n-alkanes and PAH. It was conclusively shown for both engines that the bulk of the particulate solvent organic fraction (SOF), including the PAH fraction, was unburnt Fuel.