Commercial Diesel Engine Design and Lubricant Formulation Trends
by David Doyle, CLS, OMA I, OMA II
General Manager, Tribology

The most significant factors affecting commercial over-the-road diesel engine design in the near future are going to be focused on engine downsizing while maintaining the same power output, increased fuel economy, and emission control. These factors will affect the performance requirements of oil formulations used in diesel engines. Lubricants and their additive chemistry are expected to improve engine durability, protect exhaust after-treatment systems, and improve fuel economy. Deposit control additives, friction modifiers, and antioxidants additives for heavy duty diesel engine lubricants will be the fastest growing additives emphasis for the next few years.

In order to help meet fuel economy targets the use of lower viscosity grade diesel engine oils, such as SAE 5W-30, have been, and will continue to be, introduced into the market. Both OEMs and lubricant manufactures are challenged in achieving a balance of fuel economy and engine durability. The use of improved friction modifiers is instrumental in allowing these lower viscosity lubricants to be used and still protect the engine.

These oils will be expected to provide comparable service life under more severe operating conditions. Engine downsizing while maintaining power output performance requirements will expose crankcase oils to higher operating temperatures. Engines oils will continue to be expected to keep a larger volume of contaminants in suspension than in the past and prevent excessive deposit and particulate formation. The use of bio-based fuels has also contributed to service life performance challenges for these lubricants for compatibility, acidity, and oxidative degradation that current and future formulations will address.

Control of ash deposit formation is a greater challenge as engine designs change. If the in-service engine oil does not control deposit formation in exhaust after-treatment systems, such as diesel particulate filters (DPF), the effectiveness of these systems can be reduced or damaged. Ash build up created by detergent metals used in heavy duty diesel engine oils in the DPF directly affects fuel consumption by creating increased exhaust flow restriction and backpressure, and increased regeneration frequency due to a reduction in the DPF filter soot storage capacity.

Another factor relevant to emerging diesel engine lubrication technology sometimes overlooked is the chemistry behind base number alkalinity reserve. Though the base number in heavy duty diesel engine oils have tended to decrease over the years, due to ash deposit control requirements and reduced sulfur content in fuels, an important factor is efficiency of acid neutralization by the base number chemistry. The speed and effectiveness of the oil's ability to fight acids rapidly, compared to slower reacting chemistry, is an important factor, aside from simply the value of oil's base number.

In-service oil analysis will continue to be a valuable resource in optimizing fleet reliability performance. Our fluids analysis laboratories at ALS Tribology can provide the technical resource support to work with your lubricant provider, monitor lubricant performance, and partner for achieving targeted return on investment. For further assistance feel free to contact ALS Tribology through one of our network laboratories in your region or