Additive Requirements

Regardless of vehicle and engine technologies, the basic functions of additives remain the same; namely, controlling friction, preventing wear and corrosion, maintaining cleanliness, preventing oil aging and breakdown and controlling contaminants. In addition, Wang said, automakers concerns and demands have led to the development of original equipment manufacturer specific engine oil specifications.

For existing engine technologies, fuel economy is optimized by the use of lower viscosity oil (SAE 0W-xx). Newer engine designs depend on a variety of technologies to optimize fuel economy, including gasoline direct injection, turbochargers, downsizing while increasing power output, variable valvetrains and cylinder deactivation.

They also employ down-speeding to produce higher torque at low rpm, which can result in low-speed preignition problems, he noted. Finally, variable oil pump operation, exhaust gas recirculation, diamond-like and plasma coatings, start/stop operation and new bearing materials all put heavier demands on the engine oil.

Europe, in particular, is heavily into the use of biofuel, liquid petroleum gas and liquefied natural gas. Wang observed that these fuels often contain high levels of sulfur, aromatics and gums that can increase oxidation, corrosion, nitration, acids and sludge.

On top of these concerns, compliance with emissions legislation has led to the use of particulate filters for gasoline engines that require lubricants with reduced ash content to prevent clogging. ACEA, API and ILSAC compliant oils do not cover all OEM concerns, he said. Therefore, OEMs have developed and mandated extra tests on top of industry requirements.

In China, the majority of 2016passenger cars are equipped with gasoline direct injection or turbocharged gasoline direction injection (GDI/TGDI). Volkswagen, General Motors and Chinese OEMs are aggressively pushing TGDI, and Asia is increasingly employing similar technology.

Light-duty vehicle fuel saving technologies being implemented by U.S. automakers and the additive challenges they present include:

Turbocharging – Oxidation control

Variable valvetrains/cylinder deactivation – Oil aeration control

GDI – Soot dispersancy to control chain wear

GDI/Turbocharging/Down-speeding – Low speed preignition (LSPI), oxidation, soot control

A major challenge in adopting these new technologies is controlling low speed preignition. According to Wang, LSPI results from the formation of a new flame front caused by an unknown initiator that leads to knock. Unlike standard knock, the initiator cant be described from bulk gas properties. In fact, LSPI has actually been found to occur pre- or post-ignition (similar to surface ignition).

Oronite testing has shown that engine oil components have a significant impact on the frequency of LSPI events. Various lubricant components play a role in LSPI, Wang explained. For example, calcium, iron and copper promote LSPI; molybdenum dithiocarbamate and zinc dialkyl dithiophosphate suppress LSPI; and oil degradation promotes LSPI.

The base stock was shown to impact LSPI, but Oronite found no correlation to Noack volatility. In addition to the engine oil, fuel composition and hardware design are other possible factors that contribute to LSPI.

With globalization in the passenger car industry and rapid introduction of the latest technologies in all markets, newer performance requirements such as LSPI control are quickly being adopted in most major markets, Wang said. The formulating puzzle becomes more challenging as we add more pieces.

General Motors Dexos1:2015 is the first global OEM specification to address new technologies with the addition of LSPI and turbocharger performance tests. And ILSAC GF-6 will be the first global specification targeted at TGDI engines, with the inclusion of tests for LSPI and timing chain wear protection.

To evaluate the effects of various additives on performance in modern engines, Oronite ran a field test on a fleet of taxis in Las Vegas, equipped with turbocharged GDI engines. Three cabs were run on a conventional SAE 5W-30 GF-5 oil, and three on an SAE 5W-30 Dexos1: 2015 platform. Each cab ran for 100,000 miles through two summer seasons, with an oil drain interval of 8,000 miles and samples taken at 4,000 miles.

The test showed that the prototype oil provided good control over viscosity, total acid number and total base number increase. The oil also provided good control of oil degradation and wear.

Future OEM Specs

Global fuel economy legislation is driving OEMs to demand lower viscosity engine oils. As a result, the industry is moving from SAE xW-40 to xW-30 formulations, and even further toward SAE 0W-20s. In addition, European specifications are limiting sulfated ash, phosphorus and sulfur content for both diesel and gasoline engines.

At the same time, OEM requirements demand higher quality oils to boost fuel economy, durability, cleanliness, biofuel compatibility and stability (as measured by oxidation and viscosity control). And they are adding new requirements, including control of LSPI. The impact on additive formulation are illustrated in the chart.

In closing, Wang said that OEMs will continue to increase their lubricant requirements, and fuel economy will remain a key driver for engine and lubricant design globally. Passenger car motor oil formulating technology plays both a direct and indirect role in enabling technologies to improve fuel economy and reduce carbon dioxide emissions, he related. And turbocharged, downsized gasoline direct injection engines are rapidly being introduced in many markets, including Asia.

Modern engine technologies place more severe and new performance requirements on engine oil formulations such as LSPI, turbocharger fouling, wear, oxidation and aeration control. Therefore, he concluded, formulators must be concerned with a broad range of sometimes conflicting performance needs while also being mindful of market needs such as cost/performance and supply/distribution optimization.