The Influence of Lubricating Oil Age on Emissions from an IDI Diesel 931003
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. Over the 120 hour test period the average fuel dilution of the lubricating oil was 0.36 % of the fuel used and the carbon in the lubricating oil was 7% of the emitted particulate carbon. Less than 20% of the lube oil fuel dilution could be attributed to particulate SOF in the lube oil and hence routes for unburnt and partially burnt fuel to enter the lubricating oil must exist and the most important of these is considered to be absorption near TDC with incomplete desorbtion at BDC. Also the 40 engine start-ups will contribute to the fuel dilution. The lube oil fuel dilution was shown to contribute only 3-4% of the particulate fuel fraction, which was dominated by directly absorbed unburnt fuel.