MOGAS/E85 etc.?

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rv7charlie

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Rhino,
There are several RV drivers that have been running E-gas in fuel injected Lycs for years. I've been doing it for a shorter period of time. The only vulnerable thing on the engine itself is the fuel pump, if it's old. Years ago, the pump mfgr switched the 'rubber' (diaphragms) to materials that aren't vulnerable to ethanol. Wish I could tell you the date when they switched, but I can't remember the exact date. I did talk to the mfgr at least 5 years ago; that's how I heard about the change. The core engine is just a rather low performance piston engine; it doesn't seem to care about ethanol at all. Plugs stay clean (no lead) valve stems don't stick (no lead). In some parts of the country, it's a lot easier to find premium E-gas than premium E-free, so it's nice that the engine can work with it. You still need to be sure the rest of the fuel system is compatible.
edit: more info below
 
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Vigilant1

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While possibly not relevant to the original post, it's worth noting that E10 and E15 are significantly more volatile than gasoline (or 100LL). Under some conditions (high altitudes, elevated fuel temperatures in the tank, lines, gascolator, etc) and some fuel system configurations, the resultant formation of vapor bubbles in the fuel system can cause trouble. Once we get more than about 50% ethanol, the volatility (as measured by Reid Vapor Pressure) is less than gasoline, so the likelihood of these problems decreases.
With modern EFI and in-tank pumps, vapor lock isn't a significant concern. But some planes use gravity feed to a carb that doesn't do well with bubbles.

1629428970637.png

Edited to add: The graph above was interesting to me. Has anybody got a simple explanation for the shape of that curve (i.e. why E10 would be more volatile than either pure gasoline or pure ethanol?) Thanks.
 
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Pilot-34

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Just to experiment I once started adding alcohol to the tank of a international Harvester 340 tractor.
This is a small utility tractor of about 50 horses with low compression built in about 1958.
I used it around the farm for small chores ,seldom using more than half a gallon of gasoline st a time.
Over a period of about three years starting from a full tank of pure petroleum gas I added close to 500 gallons of pure ethanol.
I did not keep track of the exact concentrations but obviously in the first year I tried pretty much every concentration from E0 to E 100.
They all worked no problems
In the remainder of that time it was obviously operating on pure ethanol again no particular problem.
The only prep work I did on the tractor was to completely drain the tank and empty The settlement bowl.
 

pjphilli

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Good stuff here. How does a newer aircraft engine, i.e. Lycoming or Continental, stand up to alcohol? Have they been made resistant to the damaging effects of alcohol like auto engines have? My current project uses a Jabiru, which is designed to use mogas, but there could be a different aircraft/engine in my future.
As I'm not an A/P, I'm hesitant to to be specific to Lycs and Continental engines beyond opinions, and it's a different discussion is talking E10 mogas or higher blends like E85.Opinion for E10: Internals of these engines are literally the same big lawn mower engines in existence for about 100 years. The parts potentially susceptible to an issue is fuel lines and gaskets/o-rings in the fuel delivery and carburetor systems. "Modern materials" like BUNA, nitrile, things used for instance on railcar gaskets hauling ethanol or related haz-mat and which are used in automobiles for last couple decades would not be an issue. I did not use ethanol fuel in my mogas STC C-85 engine because it was not approved, and because I'm not confident '1940 components would hold up. Were I doing an E-AB, I'd try try a flex fuel, fuel injected for personal fun and learning. PS: Next week when back in office I'll search out a chart of common materials and their relative compatibility with chemicals with source credited.
 

pjphilli

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While possibly not relevant to the original post, it's worth noting that E10 and E15 are significantly more volatile than gasoline (or 100LL). Under some conditions (high altitudes, elevated fuel temperatures in the tank, lines, gascolator, etc) and some fuel system configurations, the resultant formation of vapor bubbles in the fuel system can cause trouble. Once we get more than about 50% ethanol, the volatility (as measured by Reid Vapor Pressure) is less than gasoline, so the likelihood of these problems decreases.
With modern EFI and in-tank pumps, vapor lock isn't a significant concern. But some planes use gravity feed to a carb that doesn't do well with bubbles.

View attachment 114543

Edited to add: The graph above was interesting to me. Has anybody got a simple explanation for the shape of that curve (i.e. why E10 would be more volatile than either pure gasoline or pure ethanol?) Thanks.
Unfortunately this is a source of a ton a confusion, I'll try to explain a few key concepts:
1. Ethanol has a much LOWER vapor pressure than pump ready "E-0", no ethanol gas. I use 3.1 PSI for denatured fuel ethanol E-98 (denaturant is 2% natural gasoline, AKA: "C-5", also have seen it called "15 lb gas" though its RVP (Reid Vapor Pressure) is typically 12-13 PSI.)
2. The blend stock used with the oxygenate to make pump ready E10 alone is not in-spec gas! Refinery's are making a sub-octane product counting on the high octane ethanol to bring it into specification. Vapor pressure is also controlled in refining to be in-specification for the specific geography, and month of the year. In colder months and colder geographies, vapor pressures are higher than in warmer months and/or warmer geographies. This is all codified by EPA, States, and ASTM procedures.
3. Partial pressures in blends and not linear, and quite hard to predict, sort of like two liquids of different pH's... the interaction between pristine hydrocarbon gas and adding ethanol can be thought of as each component wants to do it's own thing: The gas wants to vaporize, the ethanol want to vaporize and you will see each component additive. It's a tiny jump because ethanol is so much lower vapor pressure. Once ethanol gets to that about 40% level, it's much lower vapor pressure drives the curve down. Each component of the blend is still contributing, but more of the lower value must bring the sum down...
 

Map

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I have often been using mogas with ethanol in my VW engine and there is sooo much water in it (dissolved, not visible), that I get carburetor ice at any OAT, even now, in summer. I practically have to melt it off for a while with carb heat on after high power settings before I can retard the throttle and not lose a lot of power. This does not happen when I use Avgas.
In cold weather the water becomes more visible, the mogas may look cloudy.
 

TFF

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Except for the lead issue, the base engine doesn’t care. Put the right air fuel mixture in and it will work. Putting the right mixture in, especially with varying concentrations along without melting stuff that never thought of coming in contact before is the problem. Old planes seal the cork tank floats with shellac. I know of a T craft that had an accident off field when the shellac gummed up the jet from E10. A bunch of old guys being cheap. Cost one of them a license. A bigger engine carb might have eaten it, who knows. The point is if you want to use what is experimental fuel to an airplane, you have to do the testing. Homebuilt easy to put into phase one and check it out. Certified has to go through the FAR system. I doubt E anything will ever be cart blanch for legacy airplanes, not without major STCs. At a minimum there just isn’t the mixture latitude with stock parts. When E10 came out thirty odd years ago in my area, I put some in my triumph spitfire. It ran better. It always ran a touch rich probably from needle and jet wear, and E10 leaned it out just about right. I know a couple of aircraft with factory slosh in the tanks. No way. Old bladder tanks. No way. Lots of questions needing to be answered to use it.
 

rv7charlie

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I should have added one caveat. Lycs have compressions all over the map. Any engine up to around 8.5-1 seems to run fine on premium mogas, with or without the E. The angle valve 360s, with 9-1 compression, and any custom higher compression version should be approached with a bit more caution. I think there's at least one angle valve engine in an RV being operated on premium mogas, but I'm not sure, and I'd be very cautious about ignition timing advance on those engines. Reason is simply octane and 'not great' primitive combustion chamber shape.
 

rv7charlie

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I have often been using mogas with ethanol in my VW engine and there is sooo much water in it (dissolved, not visible), that I get carburetor ice at any OAT, even now, in summer. I practically have to melt it off for a while with carb heat on after high power settings before I can retard the throttle and not lose a lot of power. This does not happen when I use Avgas.
In cold weather the water becomes more visible, the mogas may look cloudy.
Sorry, but I can make no sense of this. The quick test for alcohol in gas is to put a bit of water in a 'test tube' shaped cylinder, mark its level in the cylinder, add the gas, and shake. If there's ethanol in the gas, the 'water' level will increase. If there were 'so much water' in your gas, it would be separated out, along with some of the alcohol, and be sitting in the bottom of your tank. And would have caused the engine to stop; not ice up. Unless you sumped the tanks during preflight. You did sump your tanks during preflight, right?
 

PMD

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I am almost afraid to open this can of worms, but it IS something that is important and has in the previous post just been introduced into this thread. One of the bleeding edge research paths is the holy grail of aqueous fuels. We have been discussing E10-E100 as if it is one thing. Ethanol is SO hygroscopic that is actually changes constantly - dissolving water until it saturates and then phase separating into condensate and solution layers. Before that point, though, my information (from an aqueous fuel researcher) is that water can HUGELY benefit the combustion process by its ability to absorb energy and produce pressure within the cylinder at lower temps (i.e. also driving down NOx formation). The aqueous fuel world works mostly with surfactant chemistry to try (so far mostly in vain) to maintain a somewhat homogenous suspension of water in saturated alcohol or blends. What gets interesting is the incredibly complex and short lived chemistry of the combustion process benefits greatly from water being present - even in relatively low concentration.

So, particularly for Phil: how does the bio-fuel industry see and treat this particular issue?

(as a side note, the "good stuff" can happen at extremely low through to extremely high water contents in various fuels).

BTW: strangely, one of my "day jobs" is making and operating equipment to DEhydrate hydrocarbons (10ppm and down is my world).
 

Vigilant1

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P
If there were 'so much water' in your gas, it would be separated out, along with some of the alcohol, and be sitting in the bottom of your tank.
At lower temps (like in the carb throat) perhaps the ability of the mixture to hold water is reduced? This is what happens with dissolved solids in a solution.
 

PMD

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I have often been using mogas with ethanol in my VW engine and there is sooo much water in it (dissolved, not visible), that I get carburetor ice at any OAT, even now, in summer. I practically have to melt it off for a while with carb heat on after high power settings before I can retard the throttle and not lose a lot of power. This does not happen when I use Avgas.
In cold weather the water becomes more visible, the mogas may look cloudy.
Just be aware that carb ice for the most part is formed from atmospheric moisture within the induced air.
 

Vigilant1

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Just be aware that carb ice for the most part is formed from atmospheric moisture within the induced air.
Yes, the carb ice could be due to lower throat temps in the carb due to the higher volatility of E10 vs gasoline (or 100ll). It evaporates more easily, so makes the carb throat even colder than it would otherwise be, can form more ice from atmospheric H2O.
 

rv7charlie

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But *not* because of water in the fuel. That much water in the fuel would cause engine stoppage due to, well, no fuel. Read some NTSB accident reports. "Carb bowl found completely filled with water; engine ran fine after water removed and engine supplied with clean fuel."
 

Vigilant1

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In cold weather the water becomes more visible, the mogas may look cloudy.
At lower temps (like in the carb throat) perhaps the ability of the mixture to hold water is reduced? This is what happens with dissolved solids in a solution.
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

1629477869893.png

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.
 
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pjphilli

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I am almost afraid to open this can of worms, but it IS something that is important and has in the previous post just been introduced into this thread. One of the bleeding edge research paths is the holy grail of aqueous fuels. We have been discussing E10-E100 as if it is one thing. Ethanol is SO hygroscopic that is actually changes constantly - dissolving water until it saturates and then phase separating into condensate and solution layers. Before that point, though, my information (from an aqueous fuel researcher) is that water can HUGELY benefit the combustion process by its ability to absorb energy and produce pressure within the cylinder at lower temps (i.e. also driving down NOx formation). The aqueous fuel world works mostly with surfactant chemistry to try (so far mostly in vain) to maintain a somewhat homogenous suspension of water in saturated alcohol or blends. What gets interesting is the incredibly complex and short lived chemistry of the combustion process benefits greatly from water being present - even in relatively low concentration.

So, particularly for Phil: how does the bio-fuel industry see and treat this particular issue?

(as a side note, the "good stuff" can happen at extremely low through to extremely high water contents in various fuels).

BTW: strangely, one of my "day jobs" is making and operating equipment to DEhydrate hydrocarbons (10ppm and down is my world).
Great Question! Water in ethanol intended for blending with gasoline for use in spark ignition engines (in the USA) is limited to 1% v/v (1.26% m/m) max specification by standard ASTM D4806. Ethanol as an azeotrope with water means that there is no way to get all the water out by distillation alone... a real efficient still will only get to ~190 proof (~95% alcohol). Molecular sieves are used to absorb the remaining water to achieve ~200 proof dehydrated alcohol. This 200 proof is treated with a pHe buffer containing a trace of corrosion inhibitor (not because ethanol is corrosive, it's not. That treatment also treats the entire gallon of E10 after blending!), and typically the denaturant (2% natural gasoline) on the way and in-line between 200 proof tank and the finished product tank ready for loading. Some facilities "rack blend", add denaturant by proportional metering during load-out to truck, rail, "other".

It's not like ethanol magically grabs water everywhere it goes unless left in the open, in an essentially sealed closed system process, water will remain 30 days or 6 months later at a customer exactly what it was day-1. It's the end user in a humid environment with the gas can of a boat using a red shop rag and a rubber band as a cap that can create a problem. In the last 10 years I have had 2 incidents of water sneaking into the product. The first was a shutdown for many years ethanol plant that left stumps in various tanks. Years later new owners pushing it all into one tank, they were about a 1.35% v/v water... simple reprocessing and blend math to bring these stumps in spec. Second incident was a plant incorrectly dosed corrosion inhibitor... they added more in the railcar manway, and got the bright idea to prop open the railcar manway, and run a pneumatic diaphragm pump for 24 hours to stir from the bottom and splash into the top manway during bad weather/rain uncovered outside. They had about a 1.1 % water, so about 0.2 % pickup from poor management of the process.
 

pjphilli

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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

View attachment 114556

So, if your airplane fuel tank 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.
Nice analysis! We're on the same page... remember the maximum specification, hydrocarbon can assume "0"% soluble for all practical purposes, so at Maximum spec of 1% water volume in ethanol used for fuel, you're bringing 0.1% water to E10 blend. With care, even keeping tanks full (or empty) for long term storage, one will not get onto the lower-left of the graph... Not enough heat for me in a cub :)
 

Vigilant1

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Right. The 0.1% max water spec in E10 is probably something we can count on, out of the pump, under normal circumstances from a reputable supplier. But we know that it requires more scrupulous "fuel hygeine' than is required for 100LL to avoid getting more (undetectable, and possibly problematic) water in it.
Off the top of my head, if someone wants to burn E10, it makes sense tov
1) If buying from a retail supplier, buy from a station that sells a lot of fuel.
2) Seal your storage cans and your airplane fuel system vapor tight when in storage. There are plenty of planes with uncapped (or only mud dauber proof) fuel vents and vented fuel caps.
3) Sump your tank, but be aware that there's always going to be water in E10 fuel, even if you can't see it in a sample. If there's a lot, it could be a problem.
4) Fly often and burn off that fuel in the tanks. If in doubt, take it out of the plane and use it in your mower, car, or give it to your MIL.

I can't safely use E10 in my Sonex because of the afformentioned volatility issues. I'm lucky that real gasoline is now available fairly nearby.
 
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PMD

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Great Question! Water in ethanol intended for blending with gasoline for use in spark ignition engines (in the USA) is limited to 1% v/v (1.26% m/m) max specification by standard ASTM D4806

It's not like ethanol magically grabs water everywhere it goes unless left in the open, in an essentially sealed closed system process, water will remain 30 days or 6 months later at a customer exactly what it was day-1. It's the end user in a humid environment with the gas can of a boat using a red shop rag and a rubber band as a cap that can create a problem.
Not magic, just physics. Airplanes that sit in the sun can move a significant amount of air through the vents in a daily sun/dark cycle, and when the evening drops below dew point, the cold aluminum tank will condense the water quite readily. That water will easily drop to the bottom of a tank of gasoline, but on the way through E-x it will pretty easily be absorbed and saturate - THEN what remains will settle as a separated liquid phase. Very cold or nice inside storage will avoid much of that, but outside not so.

What I was really curious about is how aware the bio-fuels industry is of the beneficial contribution of water to combustion. As a note: I have driven an SI van running on 50% ethanol, 50% water - just in case people wonder how far things can be pushed.
 
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Vigilant1

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Not magic, just physics. Airplanes that sit in the sun can move a significant amount of air through the vents in a daily sun/dark cycle, and when the evening drops below dew point, the cold aluminum tank will condense the water quite readily. That water will easily drop to the bottom of a tank of gasoline, but on the way through E-x it will pretty easily be absorbed and saturate - THEN what remains will settle as a separated liquid phase. Very cold or nice inside storage will avoid much of that, but outside not so.
One subtle difference: Gasoline won't hold any water or take water vapor from the air. Condensation that drips in goes to the bottom. Keeping the fuel tank full reduces the amount of air/water vapor that get inspired and condensed. E10 will take water vapor out of the air (no condensation needed). Over time, if water vapor can get in, it will enter the mixture until it eventually separates.
 
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