Low-speed pre-ignition is a phenomenon that sometimes occurs in downsized, turbocharged engines operating at low speeds under heavy loads. For reasons that are not completely understood, combustion occurs in the piston chamber before sparkplug ignition, sometimes causing severe damage to the piston.

The engine oil industry thought it had addressed the problem in 2018 by introducing a supplemental passenger car engine oil category, API SN Plus. A new engine test, the Sequence IX, was intended to measure an oil’s ability to prevent LSPI. The Sequence IX was carried over into ILSAC GF-6 and its companion category, API SP, which was officially introduced on May 1.

In 2018, additive maker Lubrizol authored a Society of Automotive Engineers paper investigating LSPI protection over time. This work showed that original equipment manufacturers and lubricant formulators should look at LSPI protection throughout the oil drain interval—both when an oil has aged and when it is fresh.

This work caught the eye of some International Lubricant Specification Advisory Committee members—including Ford, which developed the Sequence IX test for API SN Plus, and General Motors, which developed its own LSPI test for the Dexos1 Generation 2 specification. A task force of OEMs, additive companies, the ASTM Test Monitoring Center, the Southwest Research Institute and Intertek engine testing laboratories was formed to investigate LSPI protection durability.

Alex Michlberger, technology manager for engine oils with the Lubrizol Corp., observed that several LSPI papers have been published over the past few years, all covering very similar areas and showing that engine calibration and oil formulation can have a significant impact on LSPI propensity. However, the papers exclusively addressed the issue in fresh oil. Only one paper, Toyota’s SAE 2013-01-2569, evaluated aged oil, Michlberger said. The paper showed that oil aging can have an impact on LSPI propensity.

Lubrizol had previously conducted an experiment in which a single engine was used to evaluate LSPI propensity over an oil drain interval and as the engine aged, Michlberger explained. “This work showed that LSPI is not a constant but changes both as oil ages and as hardware ages. It also provided insight into how and where LSPI occurs on the road under normal driving conditions and provided understanding into how the mechanisms of LSPI may change from primarily oil or fuel droplets early in the engine’s life to primarily deposit-induced as the engine ages.”

Broad industry research has shown that magnesium can mitigate LSPI propensity, and oils rich in magnesium have the capability to eliminate LSPI events in engine tests. For reasons not completely understood, calcium was found to negatively impact LSPI, and the removal of some calcium, which was then supplemented by magnesium, provided passing performance for the Sequence IX and GM’s LSPI tests. Although additive companies took different approaches, it appears that all used some level of magnesium in their latest API SN Plus formulations, which should carry over into ILSAC GF-6.

“We think that molybdenum dithiocarbamate, titanium and zinc dialkyldithiophosphates may interrupt the LSPI precursors via their antioxidant properties,” Michlberger noted. “We also know that these additives decompose over time. As the additives decompose, they are no longer available to act to prevent LSPI.”

With the knowledge that LSPI propensity can change over the life of the oil drain, he said, “The next logical question was, do different formulations age differently?”

The researchers prepared a number of samples to evaluate different approaches to LSPI mitigation. The first was a detergent rebalance, removing calcium and supplementing with magnesium. The second approach used a large amount of molybdenum, and the third incorporated a significant amount of titanium (left). “Our intention was not to indict any particular formulating strategy—only to look at ‘bookend’ solutions to formulating for LSPI—and we approached it very academically,” he said. (See results on page 36.)

Lubrizol noted that the Sequence VI fuel economy test influenced the researchers’ approach to testing for LSPI durability. The first iteration of the Sequence VI only evaluated fuel economy with fresh oil but later gained a durability component.

When Lubrizol initially presented this work to the task force, Michlberger recommended testing three oils: a baseline product with high calcium and no LSPI mitigating solution; an oil with detergent rebalanced by replacing some calcium with magnesium; and a high-molybdenum oil.

“Since the detergent rebalance removes the calcium, the bad actor, you are attacking the problem at the cause, not just treating the symptoms. We believe magnesium to be largely neutral—it’s really the removal of calcium that reduces LSPI propensity,” he explained.

At the time of writing, the leader of the task force, Ron Romano of Ford, told Lubes‘n’Greases that the test matrix that will help define a new test for LSPI protection durability has been funded and should be starting soon. “We hope we will make good progress and that we can report on our efforts by the June ASTM meeting,” he added.

The test matrix to prove the new LSPI testing method is viable is expected to cost about $350,000, and funding will be provided by task force members, including additive companies Afton, Infineum, Lubrizol and Oronite, as well as Ford, GM, Intertek and SWRI.

In addition, Kevin Ferrick of API noted that the organization will contribute about $100,000 in funding to support this work. “API does not typically fund test development, but we’re making an exception for this test considering the importance of LSPI to the ILSAC GF-6 standard,” he explained.

Commercially, this work poses many questions, as current oils may not completely resolve LSPI issues. William O’Ryan, manager of the Global Technical Support Services Group for Lubrizol, observed that “GM and Ford appear to have agreement that LSPI used oil durability is important. This would lead one to believe that there continue to be concerns in the field, and we also know that Japan OEMs have been involved in the test development task force.”

Developing an engine test is difficult. Michlberger explained that the potential for new or replacement LSPI tests for future engine oil specifications “all comes down to how the prove-out testing goes.” The engine, aging cycle and LSPI test cycle that the industry will use differ from those used and published by Lubrizol. Additionally, Michlberger stated that he conducted the oil aging in the same engine that was used for LSPI testing—similar to how the Sequence VIE operates. In contrast, the industry will do aging in a different engine.

“If things work out well and the results agree with my work, I think the task force will move quickly to establish a test. If there are issues or we get different results, then it is likely that the process will lose momentum. But with the support of Ford and GM, I think a test will eventually be developed,” Michlberger said.

O’Ryan added that Lubrizol believes the Sequence IX will continue to test fresh oil and that an LSPI durability test will be a new, separate test.
This potential change does raise some significant questions about how the change would be made and whether it would force modifications to engine oil technology that is just being introduced for ILSAC GF-6.

Ferrick noted that API has a lot to consider, but it is likely to introduce the test in a similar manner to API SN Plus, which adopted the Sequence IX LSPI test to supplement API SN and ILSAC GF-5. “This allowed API to handle an OEM concern quickly but with appropriate mandatory waiting periods to allow fair access to the new specification,” he added.

O’Ryan agreed, saying that “API SN Plus was implemented to quickly move fresh oil LSPI [testing] into an API specification on an urgent basis. This supplemental category development provided a faster track to the consumers than waiting for GF-6 development to complete.

“Now that we have GF-6 nearly in place as first licensing hits May 1, it would be extremely difficult, if not impossible, to add the new LSPI durability test to GF-6, as this would change the hurdle for GF-6 for oil marketers and additive companies. We agree that an API ‘SP Plus’ is more likely to be the course of action, assuming that the test development process is successful. If the test development is successful, we would estimate that it follows a similar timeline as SN Plus.”

API SN Plus was formally requested on July 20, 2017, with formal adoption into API 1509, the Engine Oil Licensing and Classification System, on November 9 of that year. First licensing was set for May 1, 2018.

The organization estimates that a formal request from ILSAC for API SP Plus will follow quickly after adoption of the new test method.

If successful, sources noted that they would expect GM to adopt this test into the new Dexos1 Generation 3 specification. However, many things would need to happen beforehand, including development of a precision test matrix if the prove-out matrix is successful, followed by establishment of base oil interchange and viscosity grade read-across guidelines.

After the industry has spent over $100 million to develop ILSAC GF-6, many may also wonder what the cost of this change could be.

Steve Haffner is president of SGH Consulting LLC. He has over 40 years of experience in the chemical industry, primarily with Exxon Chemicals Paramins and Infineum USA. He specializes in engine oil formulation and marketing. Contact him at sghaffn2015@gmail.com or (908) 672-8012.