Impact of Lubricant Oil on Regulated Emissions of a Light-Duty Mercedes-Benz OM611 CIDI-Engine

The Partnership for a New Generation Vehicle (PNGV) has identified the compression-ignition, direct-injection (CIDI) engine as a promising technology in meeting the PNGV goal of 80 miles per gallon for a prototype mid-size sedan by 2004. Challenges remain in reducing the emission levels of the CIDI-engine to meet future emission standards. The objective of this project was to perform an initial screening of crank case lubricant contribution to regulated engine-out emissions, particularly when low particulate forming diesel fuel formulations are used. The test engine was the Mercedes-Benz OM611, the test oils were a mineral SAE 5W30, a synthetic (PAO based) SAE 5W30, and a synthetic (PAO based) SAE 15W50, and the test fuels were a California-like certification fuel and an alternative oxygenated diesel fuel. The most important findings were that for a low-speed, low-load condition representing real-world application of this light-duty engine, the particulate emissions had a statistically significant reduction of 18% by switching from a mineral SAE 5W30 oil to a higher-viscosity lower-volatility synthetic SAE 15W50 lube oil. However, the reduction in particulate emissions would be traded off against a statistically significant increase of 33% in nitric oxides emissions. This increase was coupled to the lube oil friction characteristics since the test was performed at constant torque. In order to obtain simultaneous reduction in particulate and nitric oxide emissions for a given SAE viscosity grade, it is important to decrease the lube oil volatility and the friction characteristics through improvement of friction modifier additives.