Oil Fuel Dilution, the Russian perspective

[Sandstorm]

Using a viscosity mixing calculator (Widman's), a 30% fuel dilution in oil of 13.5 cSt would make the resulting viscosity 5.06 cSt.

View attachment 212680

The dynamic viscosity of gasoline would be around 0.38 cP (SG = 0.7), so using the calculator with dynamic viscosity units it would be as shown below. Since Oil #2 is also in cP, then disregard the units on the input boxes would be in dynamic viscosity units of cP in this case.

View attachment 212685

Thanks for the data! I think everybody including Mikhail would acknowledge this as well!
He has authored a number of peer reviewed articles in the subject matter.

When we see a 4% dilution often times we freak out and he is saying that basically there is no need to do so!

 

[kschachn]

When we see a 4% dilution often times we freak out and he is saying that basically there is no need to do so!

Why shouldn’t we? Even if you’re not concerned about the viscosity decrease there are many other reasons why fuel dilution is undesirable. It is not benign.

And I for one am still concerned about the viscosity loss.

 

[Sandstorm]

Why shouldn’t we? Even if you’re not concerned about the viscosity decrease there are many other reasons why fuel dilution is undesirable. It is not benign.

And I for one am still concerned about the viscosity loss.

I don't think it's benign either. It's malignancy however, often times, is over-exaggerated

 

[HouseTiger]

With the World War II aircraft engines and oil that had been diluted with gasoline in Antarctic conditions, those engines would have been operated at low speed when the oil was still very cold and thus very thick even with the addition of gasoline. And, they would have been throttled to a higher RPM and kept there for the entire operation of the flight.

So keeping in mind what Jetronics said, I can see where they could have gotten away with it without a problem because during the time it was run at low RPM the oil would have been much thicker and whenever they got the engine warmed up they would have been running it at higher RPM continuously and also at high load.

Also, the engines had a relatively short life span between overhauls, assuming they didn't take battle damage in the interim. They were low RPM engines that ran in the range of 1800-2200 RPM during flight. The radial engines in particular had large oil sumps, ran with what we would consider loose tolerances, and low compression ratios. Compare that to automobile engines that have 10:1 compression (or higher) and go over 2200 RPM just getting up to speed.

 

[ChristianReske]

https://de.wikipedia.org/wiki/Rechliner_Kaltstartverfahren


The Rechlin cold start method was an improvised method for cold starting piston aircraft engines at low ambient temperatures, which did not require complex heating devices for preheating and only a short lead time for the engine to start the flight. The process, which was used by the German Air Force during the Second World War, was developed before the war in the Rechlin testing center.

The basis was the addition of fuel to the engine oil, which reduced the viscosity of the lubricant and made it remain thin even when cold. After starting the engine, the fuel evaporated as it warmed up to operating temperature, causing the engine oil to regain the viscosity required for load operation. The time needed to warm up until full engine power (starting power) could be accessed was around three to six minutes, depending on the mixture ratio and the outside temperature. After around 30 minutes of flight operation, the fuel content in the lubricant was still around four to five percent, and after around one to two hours the fuel had completely evaporated. Motor gasoline with 80, 87 or 100 octane was used for the admixture; diesel fuel was generally not used.

The fuel was added after landing and the engine oil had cooled to a temperature of around 20 to 40 degrees Celsius. In older aircraft, this was done by pouring fuel directly into the aircraft's oil tank and then briefly run the engine; newer aircraft models were equipped with a permanently installed mixing system. The mixing ratio depended on the engine type, the previous flight duration (in relation to any remaining residue from the previous cold start) and the expected outside temperature at the time of the next start. Depending on the oil level in the oil tank of the dry sump lubrication, a mixing valve had to be kept open when the engine was idling for a defined time, which can be found in the mixing table, so that the admixture took place. The Rechlin testing center developed corresponding tables for this purpose in series of tests. The tests carried out by the testing center did not reveal any damage to the engines as a result of using the process; in many cases, even less engine wear was found.

 

[Sandstorm]

https://de.wikipedia.org/wiki/Rechliner_Kaltstartverfahren


The Rechlin cold start method was an improvised method for cold starting piston aircraft engines at low ambient temperatures, which did not require complex heating devices for preheating and only a short lead time for the engine to start the flight. The process, which was used by the German Air Force during the Second World War, was developed before the war in the Rechlin testing center.

The basis was the addition of fuel to the engine oil, which reduced the viscosity of the lubricant and made it remain thin even when cold. After starting the engine, the fuel evaporated as it warmed up to operating temperature, causing the engine oil to regain the viscosity required for load operation. The time needed to warm up until full engine power (starting power) could be accessed was around three to six minutes, depending on the mixture ratio and the outside temperature. After around 30 minutes of flight operation, the fuel content in the lubricant was still around four to five percent, and after around one to two hours the fuel had completely evaporated. Motor gasoline with 80, 87 or 100 octane was used for the admixture; diesel fuel was generally not used.

The fuel was added after landing and the engine oil had cooled to a temperature of around 20 to 40 degrees Celsius. In older aircraft, this was done by pouring fuel directly into the aircraft's oil tank and then briefly run the engine; newer aircraft models were equipped with a permanently installed mixing system. The mixing ratio depended on the engine type, the previous flight duration (in relation to any remaining residue from the previous cold start) and the expected outside temperature at the time of the next start. Depending on the oil level in the oil tank of the dry sump lubrication, a mixing valve had to be kept open when the engine was idling for a defined time, which can be found in the mixing table, so that the admixture took place. The Rechlin testing center developed corresponding tables for this purpose in series of tests. The tests carried out by the testing center did not reveal any damage to the engines as a result of using the process; in many cases, even less engine wear was found.

Very interesting. Thanks for the translation!

 

[widman]

Thanks for the data! I think everybody including Mikhail would acknowledge this as well!
He has authored a number of peer reviewed articles in the subject matter.

When we see a 4% dilution often times we freak out and he is saying that basically there is no need to do so!

You are mixing wrong. Using the viscosity of gasoline at 40º with the viscosity of oil at 100º. I don't have the exact viscosity of gasoline at 100ºC, but the VI is similar to single grade motor oil.

 

[ZeeOSix]

You are mixing wrong. Using the viscosity of gasoline at 40º with the viscosity of oil at 100º. I don't have the exact viscosity of gasoline at 100ºC, but the VI is similar to single grade motor oil.

The kinematic viscosity for gasoline at 100C is 0.50 - 0.60 cSt. At 40C the KV is 0.65 - 0.75 cSt.

I use the averages of 0.70 cSt for 40C (104F) and 0.55 cSt for 100C (212F).

 

[andyd]

Buy cheap oil and change it often. Easy for me to say, Camry hardly leaves the driveway. Once a yr, maybe twice, it gets changed. I'm paranoid about gunking up the VVT widgets and the oil rings. PITA job too. I've got 50$ worth of filter change tools. Sheesh! Used oil gets added to heating oil tank.

 

[Sandstorm]

Buy cheap oil and change it often. Easy for me to say, Camry hardly leaves the driveway. Once a yr, maybe twice, it gets changed. I'm paranoid about gunking up the VVT widgets and the oil rings. PITA job too. I've got 50$ worth of filter change tools. Sheesh! Used oil gets added to heating oil tank.

Agreed. There is not much price difference between a good oil (Walmart brand) vs great oil (Mobil 1) so I'll go with the great oil and change it often.

 

[oil pan 4]

Can you imagine the upper cylinder wear rate of an engine that has the lubricant diluted with a solvent at the rate of 2:1? That's just crazy to think there'd be no adverse affect.

The upper rings already see 5 to 10% fuel dilution during normal use.

 

[IndyIan]

I would guess the standard oil viscosity for NAMI tests would be something like 5W30? Maybe 10W40? Probably not 0W20 or 0W16 anyways!
So losing some viscosity isn't as big a deal.

I guess 2 strokes are the extreme example of fuel dilution around the piston and rings? and 2 stroke oil is only 15-20 weight before mixing! The bearings are typically rollers so don't need as much viscosity, but the rings and pistons aren't much different? I don't know how long you could go on a top end a modern EFI liquid cooled two stroke, if it was run as lightly and easily as the average car? Like in the 10-20hp/l range?
I probably did in the range of 4-500hrs on my air cooled IT200 dirt bike on the same top end, but we did do a lot of roads, but to do 50-55mph, 8-10hp was needed, so that's near 50hp/l, and it spent a fair amount of time near WO at over 100hp/l
It was run pretty rich though, and at 22:1.

 

[john_pifer]

Wait'll everyone here finds out how 2-stroke gasoline engines operate.

Yeah, but 2-strokes these days are all smaller engines.

Sure, there have been some larger ones (Saab). But I’m sure they didn’t last anywhere near as long as a 4-stroke.

 

[Sandstorm]

I would guess the standard oil viscosity for NAMI tests would be something like 5W30? Maybe 10W40? Probably not 0W20 or 0W16 anyways!
So losing some viscosity isn't as big a deal.

I guess 2 strokes are the extreme example of fuel dilution around the piston and rings? and 2 stroke oil is only 15-20 weight before mixing! The bearings are typically rollers so don't need as much viscosity, but the rings and pistons aren't much different? I don't know how long you could go on a top end a modern EFI liquid cooled two stroke, if it was run as lightly and easily as the average car? Like in the 10-20hp/l range?
I probably did in the range of 4-500hrs on my air cooled IT200 dirt bike on the same top end, but we did do a lot of roads, but to do 50-55mph, 8-10hp was needed, so that's near 50hp/l, and it spent a fair amount of time near WO at over 100hp/l
It was run pretty rich though, and at 22:1.

My guess would be either 5W-30 or 5W-40 (since those are the most common oil viscosities in Russia these days).

 

[chris719]

Noted automotive experts with thriving automotive industry, Russia . All joking aside, he does qualify his statements and you would need much more data across more engines to come to a solid conclusion.

 

[OilUzer]

Another benefit of thick(er) oil and short(er) OCIs.

People love to buy cars from old people who go to church once a week and a nearby grocery shopping twice a week without any long drives and/or Italian tune-ups! So it must not be a major concern.

Curious if they have any fuel dilution related issues in Italy?

 

[camrydriver111]

Noted automotive experts with thriving automotive industry, Russia . All joking aside, he does qualify his statements and you would need much more data across more engines to come to a solid conclusion.

From reading his email it sounds like they didn't do wear testing, at least in his original research. They just confirmed the engine can operate in this condition.

That engine he is refering to NAMI 4.4L was developed by Porsche together with the Russian state for Putin himself. So there would be testing for this application. Durability testing would be of high importance. When there is a nuclear holocaust you want the engine to still do its job.

He does reference other studies as well that he didn't see wear in the cylinder group. However, it is not clear what is meant by that. Did they check wear and there was none? Or did the authors of those studies also not check wear?

From UOAs we can easily see wear metals increase correlate with fuel dilution. So regardless of what he says, dilution does seem to increase wear.

 

[OilUzer]

Using a viscosity mixing calculator (Widman's), a 30% fuel dilution in oil of 13.5 cSt would make the resulting viscosity 5.06 cSt. Gasoline is around 0.55 cSt at 100C.

View attachment 212680

The dynamic viscosity of gasoline would be around 0.38 cP (SG = 0.7), so using the calculator with dynamic viscosity units it would be as shown below. Since the input units are in cP, then the resulting mixture units will also be in dynamic viscosity units of cP in this case.

View attachment 212685

Are the units in the second table in cP?

 

[ZeeOSix]

Are the units in the second table in cP?

In post 19, I corrected the gasoline viscosity from kinematic (cSt) to dynamic (cP) with the Specific Gravity factor of gasoline (approx 0.7), then used the HTHS viscosity of the oil in the calculator, I entered both the oil and gasoline in dynamic viscosity units of cP for consistent viscosity units, and it showed the oil's dynamic HTHS went from 3.5 cP to 1.97 cP with 30% fuel dilution. Fuel dilution of 30% is a lot, and would highly impact the resulting mixture viscosity.

 

[JimPghPA]

I wasn't going to say anything but this information is erroneous. Radial engines are dry sump systems with no engine mounted sump to be diluted. There are two scavenge pumps and one feed pump on nearly every system and since the F4-U was mentioned, that is precisely how the R-2800 Pratt & Whitney 18 cylinder radial worked. If any oil was diluted then it was diluted in the oil tank that was external to the engine. The tank wasn't there to replenish any burned oil but was in fact the only source of oil for the engine.

And on extreme cold start, what's sloshing around initially needs to be diluted. Dry sump, does not mean no oil.

Hay, I was not even born then, but I can understand that there had to be some oil inside those engines, and that some had to be thinned in those conditions.

If there's no significant oil in those engines, what feeds the two scavenge pumps.

If there's only just enough to lube the moving parts, that just enough could be diluted more than the tank for a cold start.

Somewhat speculating on my part, but there is room for having higher diluted oil during start. Maybe the tank was also diluted. But my (guess) would be that for real extreme cold start some gasoline into the crankcase area would provide that extra diluting, even if only for a very brief time.