Fuel Dilution "Burn-Off"

[SonofJoe]

Originally Posted By: Shannow
So much more than the 8% made it to the sump, and the lighter ends evaporated leaving the heavier fuel components that were still far lighter than the lighter oil components...


Yes. Exactly so. The whole constantly repeating cold/condense followed by heat-up/re-evaporation sequence leads to this 'distilled' accumulation of heavy ends in the oil.

My Sirion had a very ordinary, MPI, normally aspirated engine that was driven in a not particularly cold (or hot) country by a very boring driver (me!).The fact that the engine gave such high levels of fuel dilution, even when the engine was in pristine condition was a bit of a surprise but strangely I just learned to live with it. Wear metals were always very low so I figured there wasn't really anything to worry about.

 

[demarpaint]

I think of it like thinning oil paint. Once you over thin it some thinner, gas in the case of motor oil will flash off, but it will never be the same viscosity again, unless you drain some thinned paint from the can and add more fresh paint. The same holds true for oil, which is why an early change is a good idea, and bumping a grade if a used oil analysis shows the oil dropped out of grade.

 

[Shannow]

Just for conversation, I wonder what would have happened if after getting the dilution, you tried an Italian tuneup...

 

[PimTac]

Thanks for that info.


Originally Posted By: Shannow
Here's a rough guide from ALS on the types of hydrocarbons typically found in daily used hydrocarbons.

http://www.caslab.com/Forms-Downloads/Flyers/PETROLEUM_HYDROCARBON_RANGES_FLYER.pdf

Look at the Gasoline, and the heaviest shown is (roughly) dedecene.

https://en.wikipedia.org/wiki/Dodecane

(Note gross oversimplification here, there are heaps of hydrocarbon series and isomers, this is just the fully saturated straight chain for discussion).

Dodecane has a boiling point of 215C, but a viscosity of 1.34 Cst...so it's not likely to evaporate anywhere but the ring belt, and can take quite a bit of viscosity degradation.

It has a vapour pressure, which means that if left outside in a cup, it will "evaporate" to reach an equilibrium pressure with the atmosphere...and disappear, as previously observed.

 

[Bamaro]

What values would I look for on a Blackstone report that would indicate there is a problem with "fuel dilution"?

Edit - I see where there is a "Fuel %" line (mine is <.5), would it show up in any other values too?

 

[zeng]

Originally Posted By: SonofJoe
......... Wear metals were always very low so I figured there wasn't really anything to worry about.

+1
I suppose this forms the ultimate sole parameter ...... in assessing performance of a lubricant.
Others are noise.IMHO.

 

[PimTac]

Originally Posted By: zeng
Originally Posted By: SonofJoe
......... Wear metals were always very low so I figured there wasn't really anything to worry about.


+1
I suppose this forms the ultimate sole parameter ...... in assessing performance of a lubricant.
Others are noise.IMHO.


It would be nice to see several used oil analysis in order to see a trend if any. This would be especially true for 0w20 oil that has dropped in grade due to dilution. But with a lack of that analysis the prudent action would be to shorten OCI to see if that helps or step up a grade of oil as suggested earlier if one's warranty is not applicable

 

[Jetronic]

Originally Posted By: Bamaro
What values would I look for on a Blackstone report that would indicate there is a problem with "fuel dilution"?

Edit - I see where there is a "Fuel %" line (mine is div>


yes, but it's hard to discern measurement errors from fuel dilution.

All the additive levels can be lower, especially if the oil level rose.
Viscosity will be down, but what is due to dilution and what is permanent shear?

 

[SonofJoe]

Originally Posted By: Shannow
Just for conversation, I wonder what would have happened if after getting the dilution, you tried an Italian tuneup...


A Italian tuneup would directionally help but what you ideally want is not something that is wham bam fast but something that builds slowly and lasts a long time (a bit like another activity that comes to mind!). The three main determinants for stripping fuel from engine oil are blow-by gas flow rate, blow-by gas temperature and engine oil temperature. All of these increase, the faster you put load on the engine. You can add a fourth determinant which is time because for a fixed sump volume, you want the highest absolute amount of hot blow-by to strip the light fuel molecules.

Of course, you have to accept that however much you might try to strip fuel by going on a long, hot, spirited drive, even if you're successful, come the following day, when you start your engine from cold, the cycle starts all over again. It's a bit like going to the dental hygienist to get all the gunk scraped from between your teeth. It looks great for a day or two but after a couple of months it's back to the way it was originally and you're wondering why you forked out fifty quid because you might as well not have bothered!

 

[KrisZ]

Another thing to consider is that it's not pure gasoline that ends up in oil, but a combination of raw gas, partially burned gas, soot and partially combusted oil. Labs conveniently label all of this as fuel dilution, but it's a lot more complex than that. Perhaps that's the reason so many people think it can be easily burned off.

 

[kschachn]

Originally Posted By: Bamaro
What values would I look for on a Blackstone report that would indicate there is a problem with "fuel dilution"?

Edit - I see where there is a "Fuel %" line (mine is div>


Blackstone does not directly measure the fuel in the oil, and that's not a straightforward process. From what I've seen on here I have no faith in their fuel dilution numbers.

 

[Ducked]

Originally Posted By: SonofJoe
If you're concerned about how re-evaporating fuel will carryover oil into your intake system and cause deposits, use the lowest Noack oil you can get your hands on (something like Amsoil 10W30).



Does that happen much?

I suppose steam from a chip pan puts grease mist into the air, but that's quite a violent, high volume process, and I THINK the grease isn't in the vapour phase, so maybe a poor analogy.

Oil molecules get "knocked" into the vapour phase by high KE fuel molecules??

 

[SonofJoe]

Originally Posted By: kschachn
Originally Posted By: Bamaro
What values would I look for on a Blackstone report that would indicate there is a problem with "fuel dilution"?

Edit - I see where there is a "Fuel %" line (mine is div>


Blackstone does not directly measure the fuel in the oil, and that's not a straightforward process. From what I've seen on here I have no faith in their fuel dilution numbers.



It been a while since I did this but usually you would measure fuel dilution by Gas Chromatography (GC). The 'fuel' shows up as a very distinct early peak before the much heavier peaks of the engine oil. You simply integrate the areas under the various peaks to get an idea of how much fuel as a percent of the total. You can do more or less the same thing with Thermal Gravimetric Analysis (which I always trusted more than GC).

 

[kschachn]

Originally Posted By: SonofJoe
It been a while since I did this but usually you would measure fuel dilution by Gas Chromatography (GC). The 'fuel' shows up as a very distinct early peak before the much heavier peaks of the engine oil. You simply integrate the areas under the various peaks to get an idea of how much fuel as a percent of the total. You can do more or less the same thing with Thermal Gravimetric Analysis (which I always trusted more than GC).

Yeah, CG is what we used in college to measure fuel in oil. I didn't even see a TGA machine until I worked for a large company that could afford one. Isn't that mostly used to measure soot?

 

[SonofJoe]

Originally Posted By: Ducked
Originally Posted By: SonofJoe
If you're concerned about how re-evaporating fuel will carryover oil into your intake system and cause deposits, use the lowest Noack oil you can get your hands on (something like Amsoil 10W30).



Does that happen much?

I suppose steam from a chip pan puts grease mist into the air, but that's quite a violent, high volume process, and I THINK the grease isn't in the vapour phase, so maybe a poor analogy.

Oil molecules get "knocked" into the vapour phase by high KE fuel molecules??



It definitely did happen on the first generation of Audi TFSI engines. IMO, it was high levels of re-evaporating fuel that carried the light front-end of the engine oil into the intake system to gunk up inlet valves and create some of the dirtiest pistons I've ever seen.

I like the chip pan analogy. Can I pinch it!?

 

[SonofJoe]

Originally Posted By: kschachn
Originally Posted By: SonofJoe
It been a while since I did this but usually you would measure fuel dilution by Gas Chromatography (GC). The 'fuel' shows up as a very distinct early peak before the much heavier peaks of the engine oil. You simply integrate the areas under the various peaks to get an idea of how much fuel as a percent of the total. You can do more or less the same thing with Thermal Gravimetric Analysis (which I always trusted more than GC).

Yeah, CG is what we used in college to measure fuel in oil. I didn't even see a TGA machine until I worked for a large company that could afford one. Isn't that mostly used to measure soot?


TGA is probably THE most useful bits of kit for understanding the physical chemistry of engine oils. When I win the lottery and build my very own lube lab in my garden shed, the TGA machine will be one of the first things I buy.

 

[Ducked]

Originally Posted By: SonofJoe
Originally Posted By: Ducked
Originally Posted By: SonofJoe
If you're concerned about how re-evaporating fuel will carryover oil into your intake system and cause deposits, use the lowest Noack oil you can get your hands on (something like Amsoil 10W30).



Does that happen much?

I suppose steam from a chip pan puts grease mist into the air, but that's quite a violent, high volume process, and I THINK the grease isn't in the vapour phase, so maybe a poor analogy.

Oil molecules get "knocked" into the vapour phase by high KE fuel molecules??



It definitely did happen on the first generation of Audi TFSI engines. IMO, it was high levels of re-evaporating fuel that carried the light front-end of the engine oil into the intake system to gunk up inlet valves and create some of the dirtiest pistons I've ever seen.

I like the chip pan analogy. Can I pinch it!?


But like I said, I'm not sure its a valid analogy, since it seems to be actually a gas stream carrying droplets. I doubt that's happening in an engine, and your mention of "light front-end" suggests it isn't, since a gas-stream carrying droplets wouldn't be expected to be very selective.

That would seem to require an interaction at the molecular level, which I'm not sure I can get my head around. Best I can do is a high velocity fuel molecule collides with an oil molecule at the surface and knocks it into the vapour phase.

 

[SonofJoe]

Originally Posted By: Ducked
Originally Posted By: SonofJoe
Originally Posted By: Ducked
Originally Posted By: SonofJoe
If you're concerned about how re-evaporating fuel will carryover oil into your intake system and cause deposits, use the lowest Noack oil you can get your hands on (something like Amsoil 10W30).



Does that happen much?

I suppose steam from a chip pan puts grease mist into the air, but that's quite a violent, high volume process, and I THINK the grease isn't in the vapour phase, so maybe a poor analogy.

Oil molecules get "knocked" into the vapour phase by high KE fuel molecules??



It definitely did happen on the first generation of Audi TFSI engines. IMO, it was high levels of re-evaporating fuel that carried the light front-end of the engine oil into the intake system to gunk up inlet valves and create some of the dirtiest pistons I've ever seen.

I like the chip pan analogy. Can I pinch it!?


But like I said, I'm not sure its a valid analogy, since it seems to be actually a gas stream carrying droplets. I doubt that's happening in an engine, and your mention of "light front-end" suggests it isn't, since a gas-stream carrying droplets wouldn't be expected to be very selective.

That would seem to require an interaction at the molecular level, which I'm not sure I can get my head around. Best I can do is a high velocity fuel molecule collides with an oil molecule at the surface and knocks it into the vapour phase.



I've never ever thought about 'The Cooking Of Chips' from a chemical engineering point of view but I suspect what's happening isn't a million miles away from what's happening in your engine's sump.

Hot blow-by is the gas phase stripping medium in an engine. In a chip pan, the stripping medium will be steam (or more accurately flash evaporated potato juice). The steam and the various components that make up vegetable oil, will all exert their own individual vapour pressure and the mole fractions of each in the aggregate equilibrium vapour flow from the surface of the chip pan will be set according to the gas laws. The more volatile components of the chip oil will preferentially enter the gas phase just as the lightest fractions of the base oil in engine oil.

Stream stripping is a very common process in the oil and chemical industries precisely because it's useful for removing the low flash, low volatility materials that are so difficult to remove by conventional multi stage distillation. Maybe Honda need to invent a tiny steam stripper and bolt it on to their GDI engines to fix the OP's problem!

 

[Ducked]

Couple of points I find a bit confusing

"Hot blow-by is the gas phase stripping medium in an engine."

Fair enough, that's what I thought. Bur your earlier example (and the acceptance of the chip pan as a valid analogy) seemed to be suggesting that the fuel vapour was the gas stripping phase.

"The steam and the various components that make up vegetable oil, will all exert their own individual vapour pressure and the mole fractions of each in the aggregate equilibrium vapour flow from the surface of the chip pan will be set according to the gas laws. The more volatile components of the chip oil will preferentially enter the gas phase just as the lightest fractions of the base oil in engine oil."

That seems to be a description of fractional distillation, and it seems to be saying that the different fractions behave independently, (which is what I thought) whereas earlier you seemed to be saying that the fuel and the light oil fractions interact.

 

[Ducked]

The "tiny steam stripper" doesn't seem too difficult, but you'd have to make it run hot so that it never condensed out.

"I've got a tiny steam stripper" sounds better than "I've got a blown head gasket", too.