Acids and TBN

J

Messages
434
Location
Berkeley
Hi, An offline discussion regarding Acids w.r.t TBN is at an impasse. Alas ... none of us are chemical engineers. [Wink] [I dont know] We have several questions. First question is whether or not acids attack base stock. My guess is yes. As 'Kule has stated, base-stock shears just like VII molecules. Base-stock is much more likely to re-assemble itself than VII polymers. However, an acid can either prevent base stock from re-assembling itself or simply attack the carbon-carbon or carbon-hydrogen bonds because it wants an electron and will stoop very low to get it! [Smile] So, an acid can be neutralized by base molecules or by the acid molecule attacking base stock and getting the electron that it desires? Is that why TBN drops off sharply at the beginning of drain interval (such as in 3MP's oil life study) and looks like exponential decay? So, if TBN exhibits exponential decay, will it never reach zero? [Cheers!] Jae
 

Patman

Staff member
Messages
21,989
Location
Oakville, Ontario
quote:
Originally posted by Greg Netzner: And why is 3MP's TBN bobbing up & down & up like dat? [I dont know]
The addition of a half quart of fresh oil every 1000 miles is responsible for his TBN coming up on some of the samples. I'm sure that if his engine didn't burn oil (and as such only 1/4 qt was needed every 1000 miles) then his TBN would be much lower right now.
 
Messages
688
Location
Morgantown, WV
One of these days I'll get around to writing my article on TBN. I have hundreds of pages of research on the behavior of used oil sitting here but I just haven't had time to put it together yet. The variation in my TBN is no doubt influenced by the make-up oil to some degree, but the numbers are also within the test's margin of error so the slight variations should really be read as "no change". This oil is still in equilibrium. Now, what I am about to write is a gross oversimplification, and I'll expand on it sometime in the future when I write the full article. In one study I have here, TBN lost half its value within 50 hours of operation (by their scale, 1 hour of operation equals 31 miles, so half the TBN was lost in 1,550 miles) and was pretty much at equilibrium from 100 hours to 400 hours (up to 12,000 miles). The oil was pretty well shagged at this point, and its properties dropped off substantially after 400 hours. This test was on a Toyota 1.5L engine using 10W-30 SG oil. By this study's reckoning, the oil's inhibitors were used up around 100 hours (3,100 miles). TBN's equilibrium was maintaned because the degraded compounds also have inhibitive qualities. However, these are not as effective as the original inhibitors and TAN has a definite trend upward after the 100 hour mark. TAN and TBN stay fairly well in balance until 500 hours (15,500 miles), when TBN is essentially used up and TAN skyrockets. So, if this study is any guide, we could be in for a long wait on MY study. [Smile] I'll try hard to prepare my full article in the coming weeks, as it seems to be a subject with much interest. Cheers, 3MP
 
Messages
764
Location
Fairfield County, CT
quote:
Originally posted by 3 Mad Ponchos: By this study's reckoning, the oil's inhibitors were used up around 100 hours (3,100 miles). TBN's equilibrium was maintaned because the degraded compounds also have inhibitive qualities. However, these are not as effective as the original inhibitors and TAN has a definite trend upward after the 100 hour mark. TAN and TBN stay fairly well in balance until 500 hours (15,500 miles), when TBN is essentially used up and TAN skyrockets. So, if this study is any guide, we could be in for a long wait on MY study. [Smile]
Interesting intervals there! 1) 3,100 miles is close to the 3,000 mile drain interval promoted by the oil change industry 2) 15,500 miles is the exact mileage that the countdown oil life timer on a BMW 3-series starts out at. The countdown goes down quickly with an increased number of short trips and decreases slowly with long trips. The most recent analysis of Castrol "synthetic" oil from my dad's BMW showed a TBN of 1.5 after 15,000 miles of use. (No oil added over that interval) 3MP, I'm thinking your oil study can go that far or greater (!) before the TBN gets to 2, based on the fact that you're adding fresh oil regularly. Will you keep going until at least the TBN gets past equilibrium? Thanks, Jason
 
Messages
688
Location
Morgantown, WV
Hi Jason, Currently my criteria for draining the oil is: * TBN reaches 2 * viscosity exceeds the limits for a 30-weight oil * insolubles are no longer controlled by filtration * wear metals increase at an alarming rate However, as this is my first oil test, the exact criteria are still up for revision as test results require. I used to focus on flashpoint also, but the flashpoint testing is so broad that I'm not really relying on that anymore; I'll probably reduce its importance when I redesign the page down the road. I had originally thought TBN would be the determining factor but now I'm starting to think it'll be either viscosity or contamination. I'm also giving up on trying to guess. LOL Cheers, 3MP
 
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