BOQI II: The effect of HTHSV

Status
Not open for further replies.
Gokhan

Gokhan

Joined
Dec 29, 2010
Messages
5,889
Location
Paramount, California
It was a fair criticism by Shannow that the base-oil quality index BOQI favored thinner oils over thicker oils.

Originally Posted by Shannow
[Linked Image]


I realized that if I multiply the BOQI by HTHSV, I get very similar numbers for these PAO blends.

BOQI II = BOQI x HTHSV

0W-20: 200
0W-30: 210
0W-40: 220
5W-30: 180
5W-40: 190
5W-50: 190

I also did the calculation for the Newtonian base stocks using KV150 and I got similar consistency. Note that during the HTHSV measurement, VII temporarily shears to a good extent.

Another interesting thing is the units.

BOQI II = BOQI x HTHSV ~ HTHSV / (CCS x NOACK)

Since HTHSV and CCS both have cP units, they cancel. You're left with 1/NOACK. Since NOACK is a rate (fractional evaporation in one hour), it has the units of inverse time. Therefore, BOQI II has the units of time. One can then postulate that BOQI II, which is in time units, is related to the oxidation-induction time or oxidative stability of the base oil.
 
What exactly is you magic potion, sir? :)

I like your reasoning ....let me expand of your thinking.

If I look not just on units on physical meaning of represented numbers:

Ratio of viscosities at HTHSV is high temperature to cold cranking viscosities so it would be relevant to a usable range of EHL regime.
Smaller the difference the broader the range longer engine life on the same oil. Longer user buys same oil if prescribed by manufacturer.

NOACK volatility is just what fraction of oil will be lost so it is still time of oil evaporation but not oxidation
More likely it is relavant to time before an oil change. so smaller the number more often user have to change oil more oil sold by manufacturer.

From this two it is easy to deduct:
So lower the number measured in units of time the higher profit to manufacturer of blend!

That means that TIME is MONEY again! :-D
 
What's the v in hthsv? Can't remember.

Btw I thought noack was weight fraction lost so it has no units even though it's weight lost per 60 min but the final number is a % weight loss and not weight lost per time.
Just asking & not questioning your equations ...
 
Last edited:
Originally Posted by OilUzer
What's the v in hthsv? Can't remember.

Btw I thought noack was weight fraction lost so it has no units even though it's weight lost per 60 min but the final number is a % weight loss and not weight lost per time.
Just asking & not questioning your equations ...

V for viscosity.

Discussed the NOACK in glory detail in some other thread. It's an exponential decay. For practical NOACK values of less than 15% per hour or so, it's fairly linear for the first few hours of the evaporation. Therefore, NOACK, which is the decay in 1 hour, is equal to the inverse of the exponential time constant of evaporation in units of hours.
 
Noack is weight fraction lost which is a percentage. ie (w1/w)*100 where w1 is weight lost and w is total weight.
Percentage is dimensionless!

I must be missing something
grin2.gif
 
Originally Posted by OilUzer
Noack is weight fraction lost which is a percentage. ie (w1/w)*100 where w1 is weight lost and w is total weight.
Percentage is dimensionless!

I must be missing something
grin2.gif


Fractional weight loss = 1 - exp(-t*NOACK).

Here, t is in hours and NOACK is in 1/hours.

For small t and/or NOACK, the exponential can be linearly approximated as exp(-t*NOACK) ~ 1 - t*NOACK and you get

Fractional weight loss ~ t*NOACK.

In other words, for t = 1 hour,

Fractional weight loss ~ NOACK.
 
Originally Posted by Gokhan
.. NOACK is a rate (fractional evaporation in one hour), it has the units of inverse time. ...


Originally Posted by Gokhan
... NOACK is in 1/hours.


Noack is weight fraction lost and its a % (percentage).

mathematically, percentages don't have any units and are dimensionless.

Your noack unit (1/t) doesn't match the definition above. Maybe my definition of noack (above) is incorrect ...

Let's forget it ... I don't want to derail your presentation. The dimension/unit thing caught my attention. That's all
grin2.gif
 
Originally Posted by OilUzer
Noack is weight fraction lost and its a % (percentage).

mathematically, percentages don't have any units and are dimensionless.

Your noack unit (1/t) doesn't match the definition above. Maybe my definition of noack (above) is incorrect ...

Let's forget it ... I don't want to derail your presentation. The dimension/unit thing caught my attention. That's all
grin2.gif


Yes, I've explained it fully and let's not derail it further.

For example, if NOACK is 8%, the fractional evaporation is 8% in 60 minutes, 4% in 30 minutes, and 2% in 15 minutes.

Just because the time isn't put there explicitly doesn't mean that it's not part of it. Evaporation is a dynamic event and time is the crucial variable. I posted the data for the actual fractional evaporation as a function of time in the other thread I mentioned and it fits perfectly with the exponential equation I wrote here, which can be approximated linearly for small time with the NOACK being the inverse time constant.

I hope this helps.
 
Time in the NOACK test appears to me to be arbitrary.

Yes I agree that time is a consideration in it, but the units are % @ a specific temperature and time duration. My take is that given the reasoning that time is in NOACK, then temperature would need to be as well, but you cannot parse it to be a % / hr*deg C. The time is just to ensure that the sample is thermally equilibrated.

Originally Posted by Gokhan

For example, if NOACK is 8%, the fractional evaporation is 8% in 60 minutes, 4% in 30 minutes, and 2% in 15 minutes.



This is factually incorrect. It does not account for thermal equilibration and the distribution of light ends that may volitalize at some rate inconsistent with the bulk temperature rise. This is essentially similar in principle to a distillation process or a gas chromatography injection process, where some fraction volitalizes at some temperature, and it may not track linearly to your calculation.

Also, arbitrary time doesnt apply to the (length ^2) / time units of viscosity.
 
The units matter is a can of worms and I think it's unnecessary since this variable is a figure of merit, not some variable derived from scientific first principles. Figures of merit don't need to have units that fit any rules.

I can see why the following might be a decent figure of merit: HTHSV / (CCS x NOACK)

Ideally, the numerator is a variable that we want to maximize, while both variables in the denominator are what we want to minimize. All of the variables are correlated, which is not a problem. Actually, it's more correct to say that we want to maximize the ratio HTHSV / CCS and minimize 1 / NOACK. For example, if the formulator changes nothing but decreases base oil viscosity and increases the amount of VIIs such that the KV100C is held constant, the HTHS increases, the CCS decreases, and the NOACK increases. One would have to know the actual values to determine whether the figure of merit would go up or down. I would be interested in seeing this figure of merit for many oils (base oils and fully formulated).

I don't understand the rationale for the new figure of merit (BOQI II) being:
BOQI x HTHSV - HTHSV / (CCS x NOACK)
, rather than simply:
HTHSV / (CCS x NOACK)
 
Again, the fact that CCS is tested at different temperatures for different W grades makes the comparison across grades very shaky for me.
 
Originally Posted by Virtus_Probi
Again, the fact that CCS is tested at different temperatures for different W grades makes the comparison across grades very shaky for me.




This makes me wonder if this index cannot be used in the same fashion across different grades of oil. The grades would have to be separate.
 
Originally Posted by drtyler
In the beginning...

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4481060/1


Originally Posted by 1978elcamino
Not to be disrespectful, but what exactly does this mean in new member terms?




I read the information in the link, charts etc,...forgive me if this is off toptic, but... If PYB is really a high quality synthetic sold as conventional, its profitable sold at its price point. Does this make all the other full synthetic oils that cost much more than conventional mean they are just making twice the profit? Others like RP and RL maybe 4x profit? I have to think about something at work today and this seems like a good fit.
 
You can't just keep arbitrarily mashing metrics together until you get a number that meets your preconceived notions...and when it comes out closer to 100, or 1 does not validate the method.

Take the 0W grade oils, my critiscism with your original technique was that oils of the same Base oil quality gave wildly different results, thus negating it as an INDEX OF BASE OIL QUALITY....

Now you've thrown in HTHS, which as you go up in the grades (20 through 40) is the result of more polymeric VI thickeners, so now has even LESS to do with BASE OIL QUALITY.

Mashing numbers together until they make 1, or 100 is not science.
 
Oh, and you forgot to divide by colour...it's truly dimensionless, and while we know that color is impacted by additives, we've ignored that entirely to date, so why start now ?

base oil colour index.jpg
 
As @JHZR2 said, evaporation is not linear in either direction. if noack is %8 do you lose %16 in 120 min?


@Gokhan,

Another question:

Lower Noack oils will results in higher index (BOQI & BOQI II) since noack is in the denominator.
you say higher index oils are better ...

correct me if I am wrong, however you have mentioned that with some cars (di?) Higher noack oils are better and it help cleanup ivd ...
Higher noack in these cases will lower the boqi & boqi ii.

How can you universally apply the index if sometimes a lower index value would be a better choice?
 
Status
Not open for further replies.

Similar threads

Y
ACEA A3/B4 oils still relevant in 2024 for Turbo GDI 'High performance' Engines? - Hyundai ElantraN
2
Replies
32
Views
4K
edyvw
AEHaas
The Frequently Quoted “Taxi Study” SAE 2005-01-3818
2
Replies
22
Views
4K
JohnnyO
T
To change or not to change from API SN to SN+... or SP 🤔
2
Replies
25
Views
9K
02zx9r rev2
V
0W challenge with passing LL-01
Replies
5
Views
2K
vinu_neuro
redhat
New Can-Am 700 Single Cylinder Oil
Replies
10
Views
1K
FastLane
Back
Top