Very useful formula

[m37charlie]

For guesstimating TBN and total ash from component analyses:
All component concentrations in ppm
TBN ~ (Ca + 1.8Mg)/300
Ash% ~ (Mo + Zn + Mg + Ca) X 3/10000

It usually works out within a factor between 0.95 to 1.05 (+/- 5%)
Obviously, if you know an oil has only Ca and Zn and you know ash% and TBN, you can solve for Zn if the specs don't show it.
Because the ash is measured by weight and Mg has a lower molecular weight than Ca, thus the shift to Mg in low ash formulation detergents.
Since ash is limited in API SM/CJ4 and ACEA E6/E9/C1-4, it makes one think hard about "wanting moly" in oils vs. losing Zn.
Does anyone know what the "ashless" detergents and antiwear ingredients are in low ash oils, specifically?

Charlie

 

[dsmith41]

I applied the TBN formula to this UOA and got a TBN value of 8.3 which seems high. Did I do it wrong?

I also calculated for the UOA where Blackstone said TBN was 2.9 and got 8.1. That is a big difference.

 

[MGregoir]

You are solving for new TBN rather than used with this formula.

 

[m37charlie]

It only applies to new oil because the alkalinity of Ca/Mg sulfonate/phenate etc detergents get used up with use, but the actual metals hang around with different anions (breakdown products). Likewise for Zn in ZDDP. The alkaline reserve (TBN) of Ca/Mg salts only gets restored as oil gets burned and replaced by the operator; the Ca/Mg goes out the pipe as ash, the organic anions get burned to CO2, H20, etc.
You can't use the TBN formula on used oil, in other words.
But it seems to work very well on new oil. And you could use it to estimate the original TBN of used oil. And the ash formula works whenever.
People say TBN drops rapidly at first, then more slowly; I've seen exponential looking decay curves. I wonder if some of the initial drop is due to mixture with retained used oil in the motor.
Anyone know how much used oil is retained in various engines, with a drain and filter change?
I would estimate your original TBN was ~8.2, with ash ~1.0%
Not the world's strongest oil, based on Zn/P and TBN. A SM gasoline car oil?
Depends of course on the intended application.

Charlie

 

[JAG]

Very cool. Thanks. Did you develop those formulas or find them from someone else?

Sodium-based detergents are used in some oils. I suppose the formula for TBN could be modified to account for that based on molecular weight.

I never heard of ashless detergents. Did you mean ashless dispersants?

Ashless antiwear additives vary widely in terms of possibilities. Complex esters, borate esters, ashless phosphorous compounds, ashless sulfur compounds (e.g sulfurized olefins), glycerol mono-oleate, and many more. R.T. Vanderbilt's website has a lot of technical information on such additives.

 

[m37charlie]

I just noticed the relationships myself looking at oil spec numbers this summer.
I'm curious about all the ashless ingredients; by definition, with typical oil analyses we only look at the metallic (ash-forming) ingredients plus a few bulk properties.
What's used for ashless dispersants?

Charlie

 

[JAG]

Ashless dispersants are typically nitrogen containing molecules with a hydrocarbon backbone. The head is polar and the hydrocarbon backbone is non-polar, so it dissolves in non-polar base oils and the polar part grabs onto polar contaminants.