Sulfated Ash and DI Engines

[Indydriver]

I read the post by another member where a Mobil technician told him that sulfated ash was a problem for DI engines and would be a target for reduction in GF6 specs. [I can't seem to find that thread so if someone could post a link, I'd appreciate it.]

As my DD is a Mazdaspeed3, a DI, turbo problem child when it comes to oil, I am looking for the "ultimate" solution in oil choices (preferring to stick with Mobil1 or Pennzoil) and now, here's another factor to consider. Can someone who understands these things provide a primer on sulfated ash, why it's used in motor oil to start with and why it's not a good thing for DI engines?

Perusing the Mobil1 spec sheets, I find the following SA content:

0W-30 = 0.9
5W-30 = 0.8
0W-40 = 1.3

Note that Pennzoil does not publish SA specs.

I was considering trying 0W-40 in this engine to offset fuel dilution but with 62.5% more SA, this new information makes it seem like a bad idea. 5W-30 also is the only visc with HTO-06 approval, so it looks like M1 5W-30 is the best choice although it still didn't help my fuel dilution issue which makes the oil a 20 wt by 3000 miles.

Note, as an added concern about viscosity, Mazda recently issue a bulletin extending the warranty coverage on this turbo and timing chain with a very strong warning that this extended coverage was only valid if the minimum oil viscosity of 30 wt is used.

So, for those of you in the know about add packs and the role SA plays, I'm very interested in feedback on this issue with DI engines such as mine. Thanks for playing.

 

[2oldtommy]

I'll take a stab at answering your question about SA, but it is strictly not scientific. ---- So, SA is not an additive, it is a property of the base fluid from which the oil is derived. Much as low sulfer Diesel is now a requirement, it is up to the refiner to REMOVE the sulfer from the base fluids from which the oil is blended. So, a sufated ash is whatever sulfer that the refiner can not remove from the blending fluids. Take a shot guys, if I'm way off base. FWIW--Oldtommy

 

[Solarent]

The main source of Sulfated Ash in engine oils is actually from the detergents. Detergents are used for a variety of purposes - everything from preventing and removing deposits, neutralizing acidic byproducts and acting as dispersants to prevent engine sludge. The metal compounds used to create detergents is typically the what becomes sulfated ash, however it can also come from other metal containing additives used in the oil formula.

Sulfated ash is measured by treating the oil with sulfuric acid and then igniting the mixture. The residue is then measured. Oils that produce ash of 0.1% or lower are considered ashless; up to 0.6% are classed as low ash, 0.7-1% medium ash and over 1% is a high ash oil.

Engine designers have begun to look at SA as a factor in combustion chamber deposits and the precursors of emission problems. The presence of more than the optimal amount can cause excessive deposits on various parts, which can result in reduced heat transfer, pre-ignition or detonation, or both, ring sticking or breaking, plug fouling, and valve burning. This became a focus during the development of CJ-4 oils for diesels which requires low ash content to assist with the efficiency of after treatment emission systems (DPF AND SCR systems). These systems rely on clean burning in combustion chambers to minimize harmful emissions. It is not surprising that this will affect gasoline and direct injection engines in a similar way, with medium - low ash oils being preferred by engine manufacturers in these cases.

It will be interesting to see what develops in terms of ashless detergents and how they are applied. Various types of calcium sulfonate is one of the most commonly used detergents in commercial additive packages, and removing them could cause many formulators big head aches. The difficulty is that detergents prevent sludge and varnish in the crankcase, but when burned in the cylinders or when experiencing blow-by it can cause deposits. The presence of these detergents is usually identified by the calcium number found on your UOA.

 

[Solarent]

Originally Posted By: 2oldtommy
I'll take a stab at answering your question about SA, but it is strictly not scientific. ---- So, SA is not an additive, it is a property of the base fluid from which the oil is derived. Much as low sulfer Diesel is now a requirement, it is up to the refiner to REMOVE the sulfer from the base fluids from which the oil is blended. So, a sufated ash is whatever sulfer that the refiner can not remove from the blending fluids. Take a shot guys, if I'm way off base. FWIW--Oldtommy


Just fyi the hydrotreating process of Group II and Group III oils basically eliminates all the sulfur content. Not really an issue with these base oils.

 

[buster]

Quote:
"Thanks for your message, Mike. We appreciate the feedback. A slight reduction in ash is desirable for advanced engine technology such as gasoline direct injection (GDI) engine and passenger car diesel engines. With GDI engines, higher levels of ash appear to result in a higher occurrence of Low Speed Pre-Ignition. The industry is currently developing tests and specifications to address Low Speed Pre-Ignition. In the future, passenger car engine oil specifications such as ILSAC GF-6 and dexos1 (next generation) are likely to have requirements such as lower ash to address Low Speed Pre-Ignition.

As for TBN retention, it is only a single parameter that provides an indication of the used oil condition. A reduction in TBN is an indication that the overbased detergent is doing its job by neutralizing acids that form as a result of combustion. TBN should be used in combination with other used oil parameters such as oxidation, nitration, TAN (Total Acid Number), ICP metals, D4684 MRV viscosity, and D445 kinematic viscosity to determine the overall condition of the used oil.

Finally, in our experience in severe-service Las Vegas field testing, Mobil 1 engine oil TBN levels typically do not drop below 2 for vehicles with 15,000 mile oil drain intervals. Furthermore, it is our experience that those oils tend not to drop any lower when we continue to 20,000 mile oil drains.

We hope this information was both helpful and informative. Thanks again for reaching out, and for your continued support of Mobil 1."


http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2703713#Post2703713

 

[skellyman]

Originally Posted By: Solarent
The main source of Sulfated Ash in engine oils is actually from the detergents. Detergents are used for a variety of purposes - everything from preventing and removing deposits, neutralizing acidic byproducts and acting as dispersants to prevent engine sludge. The metal compounds used to create detergents is typically the what becomes sulfated ash, however it can also come from other metal containing additives used in the oil formula.

Sulfated ash is measured by treating the oil with sulfuric acid and then igniting the mixture. The residue is then measured. Oils that produce ash of 0.1% or lower are considered ashless; up to 0.6% are classed as low ash, 0.7-1% medium ash and over 1% is a high ash oil.

Engine designers have begun to look at SA as a factor in combustion chamber deposits and the precursors of emission problems. The presence of more than the optimal amount can cause excessive deposits on various parts, which can result in reduced heat transfer, pre-ignition or detonation, or both, ring sticking or breaking, plug fouling, and valve burning. This became a focus during the development of CJ-4 oils for diesels which requires low ash content to assist with the efficiency of after treatment emission systems (DPF AND SCR systems). These systems rely on clean burning in combustion chambers to minimize harmful emissions. It is not surprising that this will affect gasoline and direct injection engines in a similar way, with medium - low ash oils being preferred by engine manufacturers in these cases.

It will be interesting to see what develops in terms of ashless detergents and how they are applied. Various types of calcium sulfonate is one of the most commonly used detergents in commercial additive packages, and removing them could cause many formulators big head aches. The difficulty is that detergents prevent sludge and varnish in the crankcase, but when burned in the cylinders or when experiencing blow-by it can cause deposits. The presence of these detergents is usually identified by the calcium number found on your UOA.

100 % right ! 1 plus

 

[Indydriver]

Thanks, Buster. That's the thread I was referring to. By "Low Speed Pre-Ignition" I assume he means "knock" which we typically associate with low octane gas. Do you think it fair to interpret these comments to mean that knock can be caused in a DI engine by an oil with too much SA? If so, wouldn't this be apparent very soon after an oil change? And, if I chose to try M1 0W-40 which, by Solarent's information is a high ash oil, I'd know pretty quickly if it was causing the knock and could swap it out.

Also, thanks to Solarent for the background info. I had forgotten that the symptom of too high SA in a DI engine was described as knock which makes it very easy to identify and eliminate. I guess I just need to try some different oils and see what happens. BTW, I've been using PP 5W-30 and have large stashes of PP and M1 which is why I want to stay with one of these oils.

 

[Solarent]

I don't know enough about DI engine designs (having never owned one) to say for sure that you will notice engine knock right away. However, your reasoning seems pretty sound IMO. I would try it and see what happens.
If you get knock, then change it out, if not, then keep monitoring it because it may lead to deposits down the road. If that happens get some PEA fuel system cleaner and run it through for a couple of tanks to help get it clean again. (I'm predicting that if low SAPS oils are adopted for gasoline and diesel passenger cars then most new engines will likely be recommended to have a fuel system treatment every 25 000 miles or so as a part of routine maintenance. - we have already seen this on highway tractor such as the Cummins ISX.)

 

[A_Harman]

Pre-ignition is caused by ash deposits in the combustion chamber that build up over time, and cause localized hot-spots. You wouldn't see an immediate change if you poured in a high-SAPS oil and went for a drive. It would take, and I'm loosely estimating here, hundreds of hours and maybe 20k miles to build up significant deposits. How much oil your engine actually passes through the combustion chamber would have a big impact on deposit formation. But if you ran mid or low SAPS oils, you could retard the buildup of deposits.

I worked on heavy-duty turbocharged natural gas engines about 18 years ago, and we used ashless 15w40 gas engine oils to avoid this exact problem. The problem with ashless oils are that they have very low TBN, and do not allow long drain intervals. Since your GDI engine runs on gasoline, there is a lot of sulfur in the fuel, which requires an oil with strong TBN and consequently higher ash.

Do you have a database of UOA's on your MS3? If you know how long you can go before TBN is depleted, you could make an educated guess at how much starting TBN you need, and buy a low or mid-SAPS oil and see how long it goes. Maybe you can find a low-SAPS oil that has excellent TBN retention, and you won't be bothered with frequent oil changes while hedging your bets on ash formation in the combustion chambers.

 

[Indydriver]

Originally Posted By: A_Harman
Do you have a database of UOA's on your MS3? If you know how long you can go before TBN is depleted, you could make an educated guess at how much starting TBN you need, and buy a low or mid-SAPS oil and see how long it goes. Maybe you can find a low-SAPS oil that has excellent TBN retention, and you won't be bothered with frequent oil changes while hedging your bets on ash formation in the combustion chambers.

No, I don't have much data. I did short OCIs with conventional for 18,000 miles with PYB which seemed to do well, then switched to PP, all with specified 5W-30. The last UOA at 3300 miles on PP suffered from 2.8 % fuel dilution with a resulting 20 wt viscosity, and low FP. These numbers weren't just barely out of spec, they were way low. The TBN was still 5.9. I guess the good news is that the wear numbers were OK. Blackstone said go to 5000 and retest but, the sub-30 viscosity has me spooked especially considering the Mazda warning on their extended warranty notice. My concern over viscosity has led me to seriously consider the 0W-40 to address the dilution issue, then saw this SA deal. Im also somewhat concerned about the big jump in MRV specs as this car will see cold starts down to -10F. I'm kind of hung between treating the dilution (viscosity) issue or just accepting 3-4000 OCIs.

 

[chiks]

I have a GDI engine, and I found that using BG44-K every 15-20k miles really help clean the engine of deposits, esp i believe on piston heads which were causing pre-ignition/knocks. although it does not quite clean the intake valves that are coated with deposits due to the EGR. But my theory is that the BG44-K still helps as the intake valve opens inside and the gaseous mixture does clean the valves to some extent.

 

[MotorsportsX]

if the detergents are what cause the ash, wouldnt PU be the worst culprit. its whole purpose in life is to clean engines it seems.

 

[tribocessive]

this is all great reading; i'm especially interested in emerging technologies; we are headed towards 1.0l, tightly wound,gdi engines with durable turbochargers, all in the name of mpg+performance; motor oil is going to have to be really good.

 

[mechtech2]

I wish there was an oil that would cure DI problems.
But the best oil only addresses one facet of DI problems.
What is this oil?
Nobody knows - what seems good and logical on paper may backfire on you.

 

[Indydriver]

Originally Posted By: MotorsportsX
if the detergents are what cause the ash, wouldnt PU be the worst culprit. its whole purpose in life is to clean engines it seems.

Excellent point. Perhaps this is why Shell won't publish the SA specs for Pennzoil synthetics. I emailed the technical contact on their website and got the usual "it's proprietary information" response.

It's easy to be lazy and assume that two premium brands both meeting SN, GF-5, are going to be very similar across the board. However, every once in a while you discover a real whopper. I've been studying PDSs on 0W-20s as my two newer vehicles use them. I like to look at the MRV -40 viscosities as an ultimate cold start spec. M1 is 9200. PP is 20,800, over twice as thick!

 

[buster]

Quote:
Thanks for your message, Mike. We appreciate the feedback. A slight reduction in ash is desirable for advanced engine technology such as gasoline direct injection (GDI) engine and passenger car diesel engines. With GDI engines, higher levels of ash appear to result in a higher occurrence of Low Speed Pre-Ignition. The industry is currently developing tests and specifications to address Low Speed Pre-Ignition. In the future, passenger car engine oil specifications such as ILSAC GF-6 and dexos1 (next generation) are likely to have requirements such as lower ash to address Low Speed Pre-Ignition.



Just rethinking this due to the DI engine I now beat the heck out of everyday. I do like the fact that Mobil 1 SA is now only .8.

Note, Amsoil's SA is probably well over 1.0%. PU wouldn't be far behind with all the Ca they are using.

 

[il_signore97]

Originally Posted By: Indydriver
I read the post by another member where a Mobil technician told him that sulfated ash was a problem for DI engines and would be a target for reduction in GF6 specs. [I can't seem to find that thread so if someone could post a link, I'd appreciate it.]

As my DD is a Mazdaspeed3, a DI, turbo problem child when it comes to oil, I am looking for the "ultimate" solution in oil choices (preferring to stick with Mobil1 or Pennzoil) and now, here's another factor to consider. Can someone who understands these things provide a primer on sulfated ash, why it's used in motor oil to start with and why it's not a good thing for DI engines?

Perusing the Mobil1 spec sheets, I find the following SA content:

0W-30 = 0.9
5W-30 = 0.8
0W-40 = 1.3

Note that Pennzoil does not publish SA specs.

I was considering trying 0W-40 in this engine to offset fuel dilution but with 62.5% more SA, this new information makes it seem like a bad idea. 5W-30 also is the only visc with HTO-06 approval, so it looks like M1 5W-30 is the best choice although it still didn't help my fuel dilution issue which makes the oil a 20 wt by 3000 miles.

Note, as an added concern about viscosity, Mazda recently issue a bulletin extending the warranty coverage on this turbo and timing chain with a very strong warning that this extended coverage was only valid if the minimum oil viscosity of 30 wt is used.

So, for those of you in the know about add packs and the role SA plays, I'm very interested in feedback on this issue with DI engines such as mine. Thanks for playing.



In terms of DI engines, there are a few issues surrounding the amount of SAPS in engine oils. Firstly, as was already discussed here, the amount of calcium sulfonate can contribute to low speed pre-ignition, and thus a mid or low SAPS oil can help with this issue. A secondary issue surrounding SAPS in DI engines is intake valve deposits. It is thought that because systems such as EGR and PCV recirculate burnt oil residue and mist, these items can accumulate on the backs of intake valves in DI engines causing poor performance. Low SAPS oils are thought to help with this issue, although I don't think there are any cold hard facts about it either. Lubrizol seems to "infer" that their low SAPS additive packages help with DI intake valve deposits.

Obviously, the whole downside to low SAPS oils are that they begin with a lower TBN, and thus cannot last as long in service. Also, this is compounded by the fact that in North America, our gasoline fuel still has higher amounts of sulfur in it, thus depleting TBN quicker.

However, I'm sure that with reasonable OCI's, you can reap the "benefits" of a low SAPS oil in your turbo DI application, and verify that with UOA for the first 1 or 2 runs (especially the winter run). Then just settle on an oil and run it to that particular OCI.

Some easily obtainable Mobil 1 low/mid SAPS products are:

Low SAPS:

Mobil 1 ESP Formula 5W30
Mobil 1 ESP Formula M 5W40

Mid SAPS:

Mobil 1 ESP X1 0W30 (this one has a TBN has high as 7.x I think)


I'm sure there are other products from other companies but I don't know how obtainable they are (i.e. Walmart, etc).

Don't worry about -10F with any of these oils. For example, the many many Mercedes diesel vehicles that get filled with M1 ESP 5W40 start fine up here in Canada, and are well protected.

 

[il_signore97]

^Also, failed to mention that all of the above mentioned Mobil 1 ESP oils have HTHS values of 3.5 cP or higher, as they are targeted to euro vehicles. Therefore, they should perform very well in your turbo GDI application (in other words, they are NOT resource conserving oils such as regular Mobil 1 5W30 or PP 5W30).

 

[wemay]

http://papers.sae.org/2014-32-0091/


Although metallic compounds are widely known to affect combustion in internal combustion engines, the potential of metallic additives in engine oils to initiate abnormal combustion has been unclear. In this study, we investigated the influence of combustion chamber deposits derived from engine oil additives on combustion in a spark-ignited engine. We used a single-cylinder four-stroke engine, and measured several combustion characteristics (e.g., cylinder pressure, in-cylinder ultraviolet absorbance in the end-gas region, and visualized flame propagation) to evaluate combustion anomalies. To clarify the effects of individual additive components, we formed combustion products of individual additives in a combustion chamber prior to measuring combustion characteristics. We tested three types of metallic additives: a calcium-based detergent, a zinc-based antiwear agent, and a molybdenum-based friction modifier. Measurements of combustion characteristics after deposit formation revealed that the deposits derived from the calcium and zinc compounds facilitated auto-ignition and increased knock intensity. However, the deposits from molybdenum compounds showed no significant impact on auto-ignition. Our results showed that the chemical composition of combustion chamber deposits has specific effects relating to abnormal combustion in spark-ignited engines.

 

[artificialist]

VW 505.01 oils have a max ash content of about .8 and are typically an Xw40 viscosity. They also typically meet API gasoline engine specs, so it would be acceptable in your engine.