Impact of Engine Oil on Emissions and Fuel Economy

Hannu Jääskeläinen

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• Emissions Performance
• Fuel Economy

Emissions Performance

The properties of engine oils can affect engine emissions in a number of ways. As discussed under Exhaust Particulate Matter, heavy hydrocarbons derived from the engine oil are a known significant contributor to the organic fraction (OF) or organic carbon (OC) portion of diesel particulates [429]. Engine oil hydrocarbons have also been suspected of contributing to the nucleation mode OF and, therefore, to particle number emissions [828]. Another possible contributor to particle number emissions are high molecular mass polymers, such as viscosity modifiers, a single molecule of which could in theory be counted as a particle by particle counting instruments.

These lube oil derived emissions are controlled through lowering the amount of oil consumed by the engine. This can be achieved through (1) engine design and/or by (2) modifying oil properties, such as lower volatility, better seal compatibility to minimize leakage, and better detergency/oxidative stability to minimize cylinder deposits.

The oil consumption from heavy-duty diesel engines meeting US EPA 2004 on-highway emission standards can be estimated from a benchmarking study carried out on 4 heavy heavy-duty and 3 light heavy-duty diesel engines and operated over a cycle based on the AVL 8-mode cycle [1270]. Based on this work, the brake-specific oil consumption of these engines is estimated to vary between 0.09 to 0.45 g/kWh. This represents about 0.2% or less of fuel consumption.

For low emission diesel engines using aftertreatment, the most important emission aspect of diesel engine oil is its compatibility with exhaust aftertreatment technologies. There are three major mechanisms for possible interference between lube oil components and aftertreatment devices:

• Accumulation of ash in particulate filters, which is a source of increased pressure drop and requires periodic maintenance (cleaning) of the DPF.
• Poisoning of catalysts by certain elements from the lube oil additive package, such as phosphorus, zinc, or sulfur.
• Formation of sulfates downstream of a catalyzed DPF or other oxidation catalysts.

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