Well, that was interesting. While I'm still digesting it and will have to go back and forth several times reviewing the results according to the levels of each element, the initial takeaway for me is similar as before.
Based on ExxonMobil/Toyota's testing results, too much Ca is bad, moderate levels of Ca are ok as long as Mg levels are equivalent or higher and low levels of Ca (with moderate levels of Mg) are best. Mb & P are somewhat irrelevant but both should be present more for their primary functions rather than as specific anti-LSPI agents. As I read in another research paper recently, it advocated equal low-moderate amounts of Ca and Mg as being ideal.
Since this document indicated that it takes 1.65 times more molecules of Mg to equal Ca, Mg content (measured as ppm in oil tests) needs to be 1.65 times the amount of Ca in order to be considered "equal."
For those who want to review for themselves, I suggest looking at the results tables at the end first to see which oil compositions failed the LSPI evaluation, then review the Ca:Mg ratio in the preceding tables showing the relative amounts based on the formulas at the beginning. Then repeat that for the ones that passed LSPI evaluation but still produced LSPI events, review the Ca:Mg ratios. Repeat again for the compositions that passed LSPI evaluation and had the highest cleanliness results, review Ca:Mg ratios and so on.
Then go back and read the relational expressions/formulas at the beginning and it will make a bit more sense. You'll then have to jump from front to back, review the data, the compositions and compare to the "preferable" ranges they advocate near the middle.
Skip the middle section after they start talking about the million different compounds for each function type, unless you have an advanced chemistry degree, as it's rather irrelevant since oils never have specific ingredients on oil container labels.
It's also interesting to note that they used mineral base oils and one of those had some PAO mixed in, but no ester base oils. They also only tested 0W-20 and 0W-16 from what it stated.
Compared to the other research papers I've read, they did not focus on the effect that PAO and ester base oils have (basically said there was no difference in anti-LSPI likelihood), whereas more recent research papers indicate there is a strong correlation between base oil type and LSPI prevalance (ester being most resistant, PAO next and Group III least resistant). They also didn't cover NOACK/volatility and the effect fuel dilution has (nor flashpoint, nor octane, nor ethanol content, for that matter), along with not covering oil droplet theory vs. carbon (or other additive) deposit particle theories.
They did give some insight on recent views on SAPS content having an effect on deposits without specifically focusing on it. Low-SAPS oils are better for preventing non-carbon deposits. These can combine with carbon deposits, of course. Pretty much any compound aggregating in the combustion chambers and on valves as deposits are to be avoided (cleaned up by other methods like WAI or prevented by using catch cans or AOSes).
Just goes to show that is very difficult to come up with a truly comprehensive method of testing for LSPI, or at least nobody has achieved it due to the sheer multitude of variables. That's why I said don't take a single paper and assume it's gospel. Read many research papers and formulate your own conclusions based on their aggregate consensus vs. outlier results.
Enjoyed it, V, thanks.
Reference (link to PDF here):