This is the third of a three-part series reviewing the fundamentals of viscosity modifiers, quantifying the benefits of viscosity modifiers for engine oil performance, the demand for engine oils that help improve fuel economy and lower emissions, and finally, examining future trends in high performance engine oils specific to heavy-duty diesel engines. This article chronicles emerging HD diesel trends driven by the needs to improve engine durability, ensure emission system compatibility, and increase fuel efficiency and reduce greenhouse gas emissions. It also summarizes the continuing contribution of viscosity modifiers to high performance HD engine oils. (See Part 1 and Part 2 in this series for additional details.)

Global Trends in Engine Oil Specifications: Focus on OEM Specs

Most consumers, and even some fleet managers, haven't seen it, but there's been a substantial change in the landscape for engine oil specifications in the 21st century. Since 2000, more than 70 new engine oil specifications have emerged, including OEM specs. "The three industry drivers for heavy-duty diesel engine oil performance are to meet emissions requirements, maintain and improve engine durability under ever increasingly severe operating conditions, and now the big challenge of increased fuel efficiency and reduced greenhouse gases," said Paul Basar, regional business manager, Europe/Africa, for heavy-duty diesel engine oils.

In addition, the industry has shifted from oils that just meet the minimum API and ACEA specification requirements to exceeding specifications including multiple OEM specifications. Today?s OEM specs usually far exceed ACEA and API requirements. The benefits of having either API or ACEA and OEM approvals include extra protection in areas such as deposit control, wear protection and oil consumption reduction. These benefits are achieved by careful formulation, including selection and balancing of additive and viscosity modifiers to meet these performance needs and viscometric requirements.

Engine Oil and Viscosity Modifier Contribution to Engine Durability

Soot Handling

Soot from combustion can accumulate in diesel engine oil. If that soot agglomerates it can lead to undesirable viscosity increase and soot related abrasive wear. Viscosity increase can hinder low temperature starting, make engine oil slow to lubricant critical engine parts during cold start, and decrease fuel efficiency and increase greenhouse gases. Poorly dispersed soot (agglomerated) can cause engine wear as shown on the cam lobe pictured below.

"Soot is a key issue in the vast majority of engines in the current vehicle population; although recent field work indicates that Euro VI compliant engines produce less soot. The commercial vehicle population takes about 15 years to rotate to a new design, and that is in developed economies" adds Basar. "Therefore the control of soot in oil remains a key attribute necessary in future heavy-duty diesel engine oil specification. Soot control by engine oil prolongs the life of the engine by reducing wear resulting from soot agglomeration as well as protecting oil filters from plugging."

Dispersants and viscosity modifiers are critical enablers for the soot handling performance required in current and future diesel engine oils. Both provide a unique mechanism to performance based upon their chemical and structural design. Dispersants contain a strong polar attachment site which associate to microscopic soot particles and inhibit agglomeration, thus preventing oil thickening, plugging and wear. Dispersant viscosity modifiers contain multiple polar attachment sites while working in a similar fashion. Other types of viscosity modifiers may have a polymer backbone which associates with the microscopic soot particles and maintains the soot particle in a fine dispersion thereby preserving oil performance. This performance is most important in engine tests such as the Mack T-11, Cummins ISX or Cummins ISM. As the viscosity grade decreases, from SAE 15W-40 to SAE 5W-30 and perhaps to even XW-20, soot control performance becomes more critical as the oil's natural oil film becomes thinner allowing soot particles to cause abrasive wear.

Engine Cleanliness

Cleanliness has always been an important feature of engine oils. As OEMs increase operating temperatures to improve fuel efficiency and lower emissions, this challenge grows in importance. For example, keeping turbo-chargers deposit free and operating at peak efficiency is a demanding task and one that is essential to maintaining emissions control, fuel efficiency and performance. The trend to use aggressive turbo-charging, higher engine temperatures and longer oil drains will continue. High performance engine oil formulations containing high performance detergents, dispersants and viscosity modifiers are up to the challenge.
"VM have deposit control capability. So there are things we can do to the polymer such that the formulator of engine oil additive packages has more flexibility in problem solving," says Chris Meldrum, business manager, viscosity modifiers. "This is one of the reasons why we work closely with the additive package formulators. Design of new VM performance polymers requires close coordination with engine oil developers and early evaluation of potential new polymers in new engines to confirm field performance."

Fuel Economy

"There are drivers for future engine oil technology, and they need to be carefully balanced; one is fuel economy and the other is engine durability. The reason they need careful balancing is to achieve the improved fuel economy and lower greenhouse gas emissions from the thinner viscosity grades, without sacrificing engine durability," adds Meldrum. "That's where additive and VM chemistry comes in, and that?s where Lubrizol excels. We love to solve problems with chemistry, our line of engine oil additives and VM work together to achieve the two goals of engine durability and fuel efficiency."

Global regulations are demanding significant improvements in fuel efficiency. Today heavy-duty truck builders have met the requirements with aerodynamics, light-weight materials, tire changes, and optimized transmission gearing and engine speed. Perhaps overlooked is the significant potential that heavy-duty diesel engine oil can contribute to improvement in fuel efficiency. A study done by Lubrizol, documented in SAE papers, shows real world fuel efficiency gains of around 2% and yearly fuel cost savings of $1,569 per year (2013 diesel prices). A 2% fuel saving for a fleet of 100 trucks saves enough money each year to purchase one new premium truck!

• "Development of Long Haul Heavy Duty Vehicle Real World Fuel Economy Measurement Technique" (SAE 2013-01-0330)
• "Development of Heavy Duty Diesel Real World Drive Cycles for Fuel Economy Measurements"(SAE 2013-01-2568)

Advanced high performance diesel engine additives and viscosity modifiers are essential to formulating fuel-efficient oils. Lubrizol's latest HD engine oil additive package, in combination with advanced viscosity modifiers when used to formulate a SAE 5W-30 engine oil, has demonstrated proven in service durability and real-world fuel savings. Future HD engine oils with even lower HTHS viscosities, formulated with advanced viscosity modifiers to provide the necessary engine oil film strength to prevent scuffing wear, are on the way. (See Part 3 in this series for more details.) Future viscosity modifiers will provide friction modifier benefits, thus further improving the engine oil contribution to fuel efficiency and lower greenhouse gases.

"Three overlapping needs - emissions, fuel economy and durability - are primary drivers for modern engine oils, but the one that tops the list for the OEMs is fuel economy. Durability has already improved considerably over the past 15 years," Basar adds. "Emissions have improved by leaps and bounds; we are about 95 to 98 % better in emissions than 20 years ago. The issue that's not been fully addressed is fuel economy."

Basar speculates that within the next 10 years we may well see labeling on heavy-duty engine oils that promote fuel economy and lower GHG, improve emissions system durability and bio-fuel compatibility. The Resource Conserving designation that API allows on API SN licensed oils that pass performance parameters for gasoline-fueled engine fuel economy, compatibility with ethanol containing fuel, and low elemental phosphorus and phosphorus retention may be a forerunner for the HD model.

Emissions System Durability

Global government regulations continue to drive regulated emissions lower and lower. One parameter, particulate emissions, is being addressed by the use of diesel particulate filters (DPF). DPFs are very effective but also require periodic maintenance to remove accumulated ash. The source of the ash is mainly from metal-containing detergents in the engine oil. Detergents are found in all modern engine oil formulations and are essential to keeping the internal parts of the engine free of deposits and neutralizing acids formed during combustion. Recent oil specifications have reduced the level of ash allowed, and this has helped extend the maintenance interval on the DPFs. Trends would indicate that ash levels will remain low or continue to fall. The challenge for engine oil formulators is to maintain engine cleanliness in light of restrictions on metal containing detergents to enable emission system durability. Viscosity modifiers play a role in supplementing the performance historically provided by ash-containing anti-wear agents.

Summary
This is the conclusion of a three-part series reviewing the fundamentals of viscosity modifiers, quantifying the benefits of viscosity modifiers for engine oil performance, describing the shift to low viscosity grade engine oils for improving fuel economy and lowering greenhouse gases, and finally, examining future trends in high performance engine oils specific to heavy-duty diesel engines. This article chronicled:

1. Global trend to numerous new heavy-duty diesel engine oil specifications to meet changing engine hardware and regulatory requirements
2. Focus on OEM specifications for improved engine oil performance beyond the industry specification
3. Government-mandated improvement in fuel efficiency and reductions in greenhouse gases while improving engine oil contribution to engine durability and emission system compatibility
4. How engine oil additives and viscosity modifiers can be used to formulate high performance heavy-duty diesel engine oil to meet these challenges