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Starting in October 1993, the sulfur in diesel fuel will be lowered from 0.27 wt % average to 0.05 wt % maximum in order to reduce particulate sulfate emissions from on-highway vehicles. Given such a major change in diesel fuel, the study reported here focused on determining the most appropriate crankcase oils to choose. Using low-sulfur fuel, the study assessed the effects of crankcase oils on: emissions, wear, deposits, oil consumption, viscosity, and Total Base Number (TBN) depletion rates. The engines used were 1994 engines with low oil consumption and direct injection, such as the Detroit Diesel Company (DDC) Series 60, Caterpillar 3176B, Mack E-7, and the Caterpillar single-cylinder engine, which will be used in establishing the next oil category to be announced in 1995. The oils evaluated were SAE 10W-30 and 15W-40 oils with sulfated-ash levels of 1.0, 0.5, and 0.0 wt %.

Federal standards on diesel exhaust smoke are currently in force and standards on carbon monoxide, oxides of nitrogen and hydrocarbon emissions for the 1974 model year were issued recently by EPA. Except for smoke, relatively little information is available on the relation of fuel quality to emissions from diesel engines, but control of diesel emissions via fuel has been suggested by users, control agencies and public interest groups. To provide information on effects of fuel quality, we measured emissions from three diverse engines with fuels that exceeded the commercial range in quality of No. 1 and 2 diesel fuels. We found that fuel properties have measurable effects on emissions, but the effects are much smaller than those of engine design and operating conditions. We conclude that changing fuel quality does not represent an effective way to control emissions from today's diesel engines.