MOGAS/E85 etc.?

[Hot Wings]

Has anybody got a simple explanation for the shape of that curve

Maybe not simple:
Azeotrope

 

[Vigilant1]

Maybe not simple:
Azeotrope

Right you are! I'm ready now for Jeopardy! "I'll take azeotropes for 500"

E10 as an azeotrope: Azeotrope formation in gasoline–ethanol blends. Part 1 – Impact of nonionic on E10 distillation curve.

 

[Map]

This just in: As the temperature of the E10+water mixture decreases (in storage, in your plane fuel tank, presumably also in your carburetor throat), the ability of the mixture to hold water does decrease.
From this document: https://www.epa.gov/sites/default/files/2015-09/documents/waterphs.pdf



So, if your airplane fuel tank filled with E10 is at 70F before flight and you take a fuel sample from the sump, you might find zero water. Still, there could be up to 0.525% water (by volume) in that fuel and it wouldn't separate out (it would virtually all separate out and be visible in your fuel sample if the fuel were gasoline instead of E10). If you have 10 gallons in your tank, there could be up to 40 teaspoons (0.83 cups, about 200ml) of "dissolved" water in the E10.
Now, if we lower the fuel temperature (in the tank on a cold day at altitude, or in the carb) to 20 deg F (carb throat temps are often that low), the E10 mix can only hold about 0.35% water (by volume). At that temp, one third of the water that was in "solution" will separate out, or about a quarter of a cup in your 10 gal tank (that showed zero water when you "sumped" it). That's enough water to fill up a carb bowl or, as ice, occlude a carb throat (without any added atmospheric water, add that in as another factor toward ice formation). I am NOT saying it does that, I am saying that we can sump all we want before takeoff and if there's E10 in the tank and it could get colder at any time, then we could have water, and maybe ice, issues.

I think this describes it best. Of course I drain the sumps before the flight and NO water is visible. The engine runs fine and produces full power with the dissolved water. My carburetor is on the cold side and from evaporating the fuel it just seems to get even colder at full throttle. The air here is very dry.
I did notice when the fuel I drained from the sump is cooled and somewhat agitated, the water shows up as smaller and larger droplets.

 

[Tipsynipper]

That is the danger of using high methanol content fuel......if your fuel is on the verge of phase separation (when the water/methanol mix drops out of solution), you will have a mixture of water and methanol that will not support combustion sitting in the bottom of your carburetor due to cooling as you climb higher leading to an engine stoppage.

I would suggest that a good test to see how close you are to phase separation is to take a sample of fuel, and add perhaps 1% water, and see what happens.

Fuel injection and Throttle bodies will not suffer from the potential engine stoppage as there is no float chamber to collect the nonburnable mixture. With carburetors if you suspect your engine failure is down to water in the carb' pump the throttle (if you have an accelerator pump) to clear the water mix, or use the primer to provide an uncontaminated fuel supply. It might just get you to the field.

 

[Pops]

That is the danger of using high methanol content fuel......if your fuel is on the verge of phase separation (when the water/methanol mix drops out of solution), you will have a mixture of water and methanol that will not support combustion sitting in the bottom of your carburetor due to cooling as you climb higher leading to an engine stoppage.

I would suggest that a good test to see how close you are to phase separation is to take a sample of fuel, and add perhaps 1% water, and see what happens.

Fuel injection and Throttle bodies will not suffer from the potential engine stoppage as there is no float chamber to collect the nonburnable mixture. With carburetors if you suspect your engine failure is down to water in the carb' pump the throttle (if you have an accelerator pump) to clear the water mix, or use the primer to provide an uncontaminated fuel supply. It might just get you to the field.

Good information. One time I had a throttle cable break. I made the runway by a few feet. At the time I never thought about using the primer to get a little extra power.

 

[Vigilant1]

Fuel injection and Throttle bodies will not suffer from the potential engine stoppage as there is no float chamber to collect the nonburnable mixture.

OTOH, while carburetors without float bowls (Posa, RevFlow, AeroInjector, and other slide carbs with a needle valve to dribble fuel) don't have a float bowl to collect water, they also lack the fuel 'buffer" that a float bowl provides. So, if the fuel develops vapor bubbles in the fuel line (which ethanol blends are more prone to than gasoline or 100LL), then the engine will, at least momentarily, stumble as each bubble reaches the needle valve. These "burps" are a known issue. Even though they might not significantly reduce total power, they can mask other issues. Folks have taken off with an engine "burping" because they are used to it, then they lose power entirely at some point because, on that day, the rough running was due to something more serious.

 

[PMD]

oops, pushed extra button

 

[PMD]

Pops:

That might have worked if you had broken the mixture cable. Adding more fuel when the throttle cable breaks should give you less power as the mixture will go very rich when you add fuel from any source - especially the rather large volume delivered by primers.

Of course, the correct answer is to fly a diesel so you don't have carb heat/ice/contamination/mixture problems

 

[Tipsynipper]

In all the Ellison installations I have installed I have always included a bleed return to the fuel tank via a restrictor at the TBI inlet. This way the fuel delivery to the TBI is always "clean"......these bleeds have primarily been included so that Mogas (as we call it in the UK, gas as you would call it in the USA?), any vapor bubbles are purged back to the fuel tank. To prove the efficacy of the bleed I roll inverted with the normal fuel supply selected rather than the flop tube, the engine will run down, but as soon as I return erect the engine power is restored. A benefit of this system is that a higher volume of fuel is circulating which aids cooling of the fuel system. In the UK we are restricted to using Mogas to temperatures below 20deg C, however, I have proved these systems at temp's up to 30 C and 10,000 in my RV-4.

 

[pjphilli]

That is the danger of using high methanol content fuel......if your fuel is on the verge of phase separation (when the water/methanol mix drops out of solution), you will have a mixture of water and methanol that will not support combustion sitting in the bottom of your carburetor due to cooling as you climb higher leading to an engine stoppage.

I would suggest that a good test to see how close you are to phase separation is to take a sample of fuel, and add perhaps 1% water, and see what happens.

Fuel injection and Throttle bodies will not suffer from the potential engine stoppage as there is no float chamber to collect the nonburnable mixture. With carburetors if you suspect your engine failure is down to water in the carb' pump the throttle (if you have an accelerator pump) to clear the water mix, or use the primer to provide an uncontaminated fuel supply. It might just get you to the field.

Quick comment: Methanol is not Ethanol... Methanol is quite corrosive and has a max specification as natural yeast metabolite existing in trace quantities of 0.5% per ASTM D4806 fuel ethanol specification. In practice, quantities are <0.1%, 0.05% is a general expectation for methanol, near the lower end of GC accurate detection. It's used in racing, but those engines may see a only few minutes of run-time before a complete tear down, like the top-fuel dragsters as example.

 

[Tipsynipper]

Sorry, my mistake.....I meant Ethanol.

What octane is the E85 you guys are talking about?

We are fortunate in the UK that 97 octane unleaded (E5) is available, which is what I use in my RV with Superior O320 Lyc. Running high compressions is a good way to damage pistons due to detonation. Sadly Lycomings and most big bore air cooled engines make so much mechanical noise that a modern injection system can't differentiate between the noise and knocking.

No one has mentioned the damage that high temp Tetra Ethyl Lead does to cylinder heads and Stainless ex' systems. It is corrosive, which is what erodes away exhaust ports and ex' systems.

 

[rv6ejguy]

Quick comment: Methanol is not Ethanol... Methanol is quite corrosive and has a max specification as natural yeast metabolite existing in trace quantities of 0.5% per ASTM D4806 fuel ethanol specification. In practice, quantities are <0.1%, 0.05% is a general expectation for methanol, near the lower end of GC accurate detection. It's used in racing, but those engines may see a only few minutes of run-time before a complete tear down, like the top-fuel dragsters as example.

I've run M85 extensively in street and race cars for a few years when it was available here at a cardlock, winter and summer. Problems encountered were hardening of some rubber hoses, swelling of others and hard cold starting in winter. Otherwise no other issues. Plugged the car in in winter and changed the hoses to methanol resistant ones. No draining of fuel, no water problems. Allowed super high boost pressures and no ignition retard, making impressive hp figures. Probably have around 40,000km running the stuff in total on several different turbo cars. Fuel economy wasn't good but I was legging it most of the time too.

 

[Bigshu]

What octane is the E85 you guys are talking about?

The actual % is rarely that high here in the Midwest. It varies with time of year (due to the average temperature fluctuations). Typically, terminals offer high ethanol blends from 50 to 75%. It depends on where it's going to be sold. As to the octane, ethanol is an octane enhancer, and a 10% blend will give a 3 to 5 point increase. It takes 83 octane neat unleaded up to 87. It takes 91 octane neat premium up to 94. I think the highest octane we posted for a blend recipe was 104, but I don't remember the ethanol % (I'm retired, so the memory is going!). The thing about adding ethanol is that it effects the vapor pressure as well, so you see a drop in fuel economy due to increased evaporation (keep your tanks full to minimize that). Also, it has a strong affinity for water vapor, and entrained water in your fuel, so there's chances for phase change dropping water into your tank, or pulling water/sediment into your fuel line. Check those fuel filters!

 

[rv6ejguy]

The thing about adding ethanol is that it effects the vapor pressure as well, so you see a drop in fuel economy due to increased evaporation (keep your tanks full to minimize that).

I hope the evaporation rate in a closed but vented tank isn't high enough to perceive a drop in fuel economy from the time you fill it to using it.

The fuel economy drop is due to the lower heating value of ethanol being (27 MJ/kg) vs. 43 for gasoline and the fact that the stoichiometric ratio is about 9 to 1 for pure ethanol vs. around 15 for 100LL.

 

[Bigshu]

I hope the evaporation rate in a closed but vented tank isn't high enough to perceive a drop in fuel economy from the time you fill it to using it.

Not a lot, but 10% ethanol raises RVP about one pound. If you run off the bottom half of the tank, you get a lot of moisture in through the vent, which condenses, drops into the tank, and can be brought into suspension by the ethanol. Water doesn't burn, so the wet fuel gives less power, meaning more is needed to compensate. We got grief all the time from drivers claiming less MPG. On the other hand, their fuel systems were cleaner than a hound's tooth...

 

[tspear]

Not a lot, but 10% ethanol raises RVP about one pound. If you run off the bottom half of the tank, you get a lot of moisture in through the vent, which condenses, drops into the tank, and can be brought into suspension by the ethanol. Water doesn't burn, so the wet fuel gives less power, meaning more is needed to compensate. We got grief all the time from drivers claiming less MPG. On the other hand, their fuel systems were cleaner than a hound's tooth...

How do you get a lot of condensation caused by the vent? Even assuming you get a one for one replacement of volume of used fuel (ethanol) with 100% warm saturated air and fly somewhere cold (or let it sit overnight); that is not much water compared to the ethanol in the tank. Even as the temp swings from night/day do not cause a significant change of air in the tank. If it did, cars and planes and other vehicles would be blowing up all over the place. They all rely upon a basic premise of fuel saturation in the air to prevent ignition.

Tim

 

[rv6ejguy]

I find lots of folks theorizing about water separating with alcohol fuels. You need a lot of water in the fuel before this will happen and it's not going to happen under normal circumstances with a fuel tank and small vent. In Canada, people used to add little bottles of methanol to take up any water in the gasoline to prevent that water from freezing in the lines supposedly. We'll that almost never happened so they were wasting their money however the theory is sound. Alcohol absorbs the water and allows it to be carried through the system. In any normal quantities, you will notice no difference in engine performance.

We use water/ methanol injection (ADI) on Reno race planes where the ADI rate may reach over 25% of the fuel flow rate (12.5% water). They run just fine.

I've run M85 a lot in a climate where OAT can change up to 20C in an hour and go down to over -40C in winter. This would have resulted in high condensation rates inside the tank IF there was saturated air inside. Never had any water issues. Engines never skipped a beat.

 

[dwalker]

I find lots of folks theorizing about water separating with alcohol fuels. You need a lot of water in the fuel before this will happen and it's not going to happen under normal circumstances with a fuel tank and small vent. In Canada, people used to add little bottles of methanol to take up any water in the gasoline to prevent that water from freezing in the lines supposedly. We'll that almost never happened so they were wasting their money however the theory is sound. Alcohol absorbs the water and allows it to be carried through the system. In any normal quantities, you will notice no difference in engine performance.

We use water/ methanol injection (ADI) on Reno race planes where the ADI rate may reach over 25% of the fuel flow rate (12.5% water). They run just fine.

I've run M85 a lot in a climate where OAT can change up to 20C in an hour and go down to over -40C in winter. This would have resulted in high condensation rates inside the tank IF there was saturated air inside. Never had any water issues. Engines never skipped a beat.

As I mentioned earlier, I've watched for this and in the past 10+ years of using E85 in cars and boats I've seen maybe 3 cases of actual phase separation. All three were in boats that were docked full time and left to sit for months. I've never seen it in an automobile. Even in the deep South where we see very high humidity.

Another thing- "pump" E85 is not very consistent, with it showing between e70 and e90. This is fine for most applications. However for highly tuned turbo cars we mixed our own from verified E100 and 87oct pump gas.
I would likely do the same for an aircraft, although one fitted with a flex fuel sensor making the fuel and timing corrections would likely work just fine.

 

[reo12]

000000000

This is a pleasant and welcome surprise to me seeing curiosity and exploration in alternative fuels on this forum. Many of the post made are technically pretty close, enough within "Ozark Math" that the points made are absolutely valid, e.g: concepts of increased cooling (That's from higher latent heat of vaporization versus gasoline), the fuel mileage observations on non-optimized engines (not taking advantage of effective ~116 octane with higher compression), the fact it will clean a dirty system, it will affect rubber not formulated to handle it, etc.

A couple comments for clarity, and disclosure: I'm in this biofuels industry serving as Technical Director for my employer. There was somewhere above mentioned similar to "Ethanol does not mix in gasoline because its polar opposite to petroleum gasoline". That's 100% in error. Not all alcohols, but Ethanol is what's called a polar-covalent compound. Ethanol is 100% miscible into covalent hydrocarbon gasoline, at any concentration. Ethanol being polar-covalent means its also 100% miscible in water at any concentration (why melting ice in your scotch and water does not separate into layers you notice while sipping it.). Something not typical in industry, but common in the gallon gas can of lawn mower fuel sitting for a few years is "phase separation". E-XX (say E-10) retail gasoline will absolutely have the ability to absorb water. It's part of why gas lines aren't freezing in the winter from water ice. The tiny bit of water you may see when you check tanks and gascolator on pre-flight would not be found running an ethanol fuel because it will be dissolved into the fuel...BUT it can only hold so much polar water before rejection by the covalent hydrocarbon. The ethanol/water will phase separate and settle below the hydrocarbon. Phase separated fuel should never be used in an internal combustion engine.

The only time I've ever seen microbiological activity in tanks has been in fuel storage hydrocarbon gas tanks, diesel, etc.. If tanks are not sumped regulary just like you do on pre-flight, the water that condenses or infiltrates from somewhere will develop into a substantial layer (Think fuel tanks on a ship... water added as fuel is consumed for ballast as an example). This water layer on the bottom is where microorganisms will get a foot-hold.

Very happy to discuss, offer opinion, etc as desired on this topic. Be Safe and Well - Phil


Hi Phil,
My information came from a talk a petrochemical engineer gave at a joint SME/ASM meeting in Grand Rapids, MI whew - some 10-12 years or so ago. I had my personal experience using E-85 to clean the fuel system of a chain saw and seeing the oil separate from suspension in the unused fuel remaining in a milk jug. I asked of this and it was he that went into the whole phase change & polar charge - organic chemistry realm that most of us had not dealt with since high school/college chemistry. If something was stated wrong - or - interpreted improperly - I certainly do appreciate any discourse on your part. I enjoy learning.

I owned several different businesses over the past 40+ years in metalworking, manufacturing and mining. My neighbor operates a dry marine service. I also worked more recently for a few years in a materials consulting lab. I have seen the results of microbiological activity in fuel on a number of occasions. Some personal - in gasoline and diesel fuel systems and one from my neighbor on a boat. While at the lab, we had a marine surveyor who was dealing with a boat that had an effected fuel system. It entered discussion with my boss as he had brought us the most vivid example of anaerobic pitting I will likely ever see - a stainless steel propeller shaft from a twin screw boat that had been moored in mud against the river bank. The pits were so severe that the shaft broke from fatigue and a portion of shaft and the prop were lost. I still have the scrap part of that shaft. I'd like to see the prop and piece of shaft that are lying on the bottom of Lake Michigan.

 

[pjphilli]

As I mentioned earlier, I've watched for this and in the past 10+ years of using E85 in cars and boats I've seen maybe 3 cases of actual phase separation. All three were in boats that were docked full time and left to sit for months. I've never seen it in an automobile. Even in the deep South where we see very high humidity.

Another thing- "pump" E85 is not very consistent, with it showing between e70 and e90. This is fine for most applications. However for highly tuned turbo cars we mixed our own from verified E100 and 87oct pump gas.
I would likely do the same for an aircraft, although one fitted with a flex fuel sensor making the fuel and timing corrections would likely work just fine.

Great Observation! Been away for awhile, and oh my I never got around to discussing "E85". E-85 is the most inconsistent fuel one can get unless you blend it yourself. Its standard is ASTM D5798 "....Flexible- Fuel Automotive Spark Ignition Engines". I mentioned somewhere the changes to vapor pressure in gasoline formulation that will vary by geography, season, and in "pollution control areas", aka: big cities with hazy skies. This is why E85 is so inconsistent, and of course cold starting with low vapor pressure ethanol.

"E-85" is a generic term for any fuel between E-51 and E-85. Note the "number" reflects the % of Denatured Ethanol... since denaturant is limited to "2%" (legally EPA and TTB says 1.96-2.49), your E-85 is actually closer to 83% ethanol, 17% natural gasoline. In many places, upper midwest, plenty of cold but not too hot summers, and the large overlap in allowable vapor pressure bands based on seasonality/temps/geography means allowable vapor pressure is generally met with E70 in the late fall/winter and early spring to keep vapor pressure high enough for the engines to start, and E85 in the warmer months to drive vapor pressure back down to control emissions when filling your tanks.

As it's becoming more available and being blended in more and more terminal rack systems, you'll see everything from the E51 to E85 as a function of the blend-stock being used by the terminals and the post blend vapor pressure requirements. Since any flex-fuel car can burn anything E0 to E85, there's no specific labeling requirement what exactly the ethanol blend is. The only retailers who would even know that is those with "blender pumps" making mid-level blends, >E15 to E-50, coming out the same pump hose. They need to know so they know where to set the blend between "E85" and "E10", or other fuel they are selling.