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]

Rechliner Kaltstartverfahren – Wikipedia

de.wikipedia.org

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]

Rechliner Kaltstartverfahren – Wikipedia

de.wikipedia.org

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).