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How long can E85 sit?

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So mowing a few lawns, I can say that 3-4 gallons of gas can last me 2 months without too much of a problem. However, gasoline obviously can't sit forever as its components separate out. My question though, is how much does the much higher ethanol content affect "shelf life" if you will?

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How long can E85 sit ?  Longer than I can  ;D

 

 

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MEMORANDUM

SUBJECT: Water Phase Separation in Oxygenated Gasoline

- Corrected version of Kevin Krause memo

FROM: David Korotney, Chemical Engineer

Fuels Studies and Standards Branch

TO: Susan Willis, Manager

Fuels Studies and Standards Group

On May 26, 1995, Kevin Krause finalized a memorandum

describing the conditions under which water phase separation will

occur in oxygenated gasolines.  Recently, several errors were

discovered in that memorandum.  I have made the necessary

corrections, and now resubmit the complete text of Kevin's memo

for your review and approval. 

Introduction

With the introduction of oxygenated gasoline came the

concern of water phase separation.  Water in gasoline can have

different effects on an engine, depending on whether it is in

solution or a separate phase, and depending on the type of engine

being used.  While separate water phases in a fuel can be

damaging to an engine, small amounts of water in solution with

gasoline should have no adverse effects on engine components.  If

precautions to prevent water from entering the fuel system are

taken, water phase separation will likely not occur.

Discussion

Oxygenated fuels usually contain either ethanol or methyltertiary-butyl-ether (MTBE).  Other possible oxygenates include

ethyl-tertiary-butyl-ether (ETBE), tertiary-amyl-methyl-ether

(TAME), and tertiary-butyl-alcohol (TBA).  Chemically, ethanol

and MTBE behave differently.  Ethanol, for example, will readily

dissolve water, and is considered infinitely soluble in water.

MTBE, on the other hand, has little affinity for water, and can

only be dissolved in water to a content of 4.3 volume percent (at

room temperature).  Therefore, ethanol/gasoline blends can

dissolve much more water than conventional gasoline, whereas

gasoline/MTBE blends act very much like conventional gasoline

when in the presence of water.

 

 

 

Since ethanol and water readily dissolve in each other, when

ethanol is used as an additive in gasoline, water will actually

dissolve in the blended fuel to a much greater extent than in

conventional gasoline.  When the water reaches the maximum amount

that the gasoline blend can dissolve, any additional water will

separate from the gasoline.  The amount of water required (in

percent of the total volume) for this phase separation to take

place varies with temperature, as shown in Figure 1.  As an

example, at 60 degrees F, water can be absorbed by a blend of 90%

gasoline and 10% ethanol up to a content of 0.5 volume percent

before it will phase separate.  This means that approximately 3.8

teaspoons of water can be dissolved per gallon of the fuel before

the water will begin to phase separate.

Since MTBE has much less affinity for water than does

ethanol, however, phase separation for MTBE/gasoline blends

occurs with only a small amount of water, as shown in Figure 2.

A blend of 85% gasoline and 15% MTBE can hold only 0.5 teaspoons

at 60 degrees F per gallon before the water will phase separate.

For comparison, one gallon of 100% gasoline can dissolve only

0.15 teaspoons water at the same temperature.  These figures are

far below the 3.8 teaspoons which will cause phase separation in

the 90/10 ethanol blend.

 

 

 

Water can enter gasoline engines in two ways: in solution

with the fuel or as a separate phase from the gasoline.  Water in

solution operates as no more than an inert diluent in the

combustion process.  Since water is a natural product of

combustion, any water in solution is removed with the product

water in the exhaust system.  The only effect water in solution

with gasoline can have on an engine is decreased fuel economy.

For example, assuming a high water concentration of 0.5 volume

percent, one would see a 0.5 percent decrease in fuel economy.

This fuel economy decrease is too low for an engine operator to

notice, since many other factors (such as ambient temperature

changes, wind and road conditions, etc.) affect fuel economy to a

much larger extent.

Water as a separate phase, however, can have differing

effects on gasoline engines, depending on whether the engine is

two-stroke (generally, smaller engines) or four-stroke (generally

automobile engines).  In the case of conventional and MTBEblended gasolines, when a water phase forms, it will drop to the

bottom of the fuel tank, and can therefore be drawn into the

engine by the fuel pump.  Therefore, large amounts of water will

prevent the engine from running, but no engine damage will

result.

Phase separation in ethanol-blended gasoline, however, can

be more damaging than in MTBE blends and straight gasoline.  When

phase separation occurs in an ethanol blended gasoline, the water

will actually begin to remove the ethanol from the gasoline.

Therefore, the second phase which can occur in ethanol blends

contains both ethanol and water, as opposed to just water in MTBE

blends and conventional gasoline.  In the case of two-stroke4

engines, this water-ethanol phase will compete with the blended

oil for bonding to the metal engine parts.  Therefore, the engine

will not have enough lubrication, and engine damage may result.

In the case of four-stroke engines, the water-ethanol phase may

combust in the engine.  This combustion can be damaging to the

engine because the water ethanol phase creates a leaner

combustion mixture (i.e. air to fuel ratio is higher than ideal).

Leaner mixtures tend to combust at higher temperatures, and can

damage engines, particularly those without sensors to calibrate

air to fuel ratios.

Phase separation, however, generally only occurs when liquid

water (as opposed to water vapor) is introduced to the fuel

system.  If tank vents are left open, either in the engine being

operated, or at a fuel distribution station, water can enter the

fuel system in the form of rain (or spillage, etc.) or through

the air in the form of moisture.  Also, since conventional

gasoline absorbs very little water, there is often a layer of

water present at the bottom of a filling station tank normally

used to store conventional gasoline (water is more dense than

gasoline, and will therefore sink to the bottom).  Before an

oxygenated gasoline is added to such a storage tank for the first

time (particularly ethanol-blended fuels), this water must be

purged from the tank to prevent the water from removing any

ethanol from the fuel.

Since the solubility of water in both gasoline and air

decreases with a decrease in temperature, water can enter a fuel

system through condensation when the atmospheric temperature

changes.  For example, assume a tank containing conventional

gasoline contains only one gallon of fuel.  Assume also that it

is closed while the outside temperature is 100 degrees F with a

relative humidity of 100 percent.  If this tank is left sealed

and the temperature drops to 40 degrees F, water will likely

condense on the inside of the tank, and dissolve in the fuel.  In

order for enough water to condense from the air to cause

gasoline-water phase separation, however, there must be

approximately 200 gallons of air per gallon of fuel over this

temperature drop (100 to 40 degrees).  Since oxygenated fuels can

hold even more water than conventional gasoline, it is even more

unlikely that enough water will condense from the air to cause

gasoline-water phase separation. 

Another way water can enter gasoline is through absorption

from the air.  Water, in the form of water vapor, can dissolve in

gasoline.  The more humid the air, the faster the water vapor

will dissolve in the gasoline.  Due to chemical equilibrium,

however, assuming a constant temperature, phase separation will5

never occur if the only source of water is from the air.  Only

enough water to saturate the fuel can enter the system, and no

more.  Water vapor, however, dissolves in gasoline very slowly,

even at very high humidity.  For example, at a constant

temperature of 100 degrees F and relative humidity of 100%, it

would take well over 200 days to saturate one gallon of gasoline

in an open gasoline can (assuming the only source of water is

water vapor from the air).  Water absorption from the air is far

slower at lower temperatures and humidities.  (At a temperature

of 70 degrees and relative humidity of 70%, it would take over

two years to saturate one gallon of conventional gasoline in the

same gasoline can.)  Again, oxygenated gasolines can hold more

water than conventional gasoline, and would therefore take much

longer to saturate with water.

Conclusion

 

Water phase separation in any gasoline is most likely to

occur when liquid water comes in contact with the fuel.  (Water

in the form of moisture in the air will generally not cause phase

separation.)  Water which is in solution with gasoline is not a

problem in any engine, but as a separate phase it can prevent an

engine from running or even cause damage.  Since oxygenated

gasolines, however, can hold more water than conventional

gasoline, phase separation is less likely to occur with

oxygenates present.

For any gasoline, simple precautions to prevent phase

separation from occuring should be taken.  First of all, gasoline

should not be stored for long periods of time, especially during

seasonal changes which usually have large temperature changes

associated with them.  (For both oxygenated and conventional

gasolines, gumming can also occur which is detrimental to any

engine.)  If it is unavoidable to store gasoline for a long

period of time, one should be sure that the tank if full to

prevent condensation of water from the air, and the addition of a

fuel stabilizer should be considered.  Lastly, care should be

taken not to allow water into the fuel sytem while filling fuel

tanks or operating the engine -- in the form of rain or a spash,

for example.

 

 

http://epa.gov/oms/regs/fuels/rfg/waterphs.pdf

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GIO..it's a question I have wondered about as well everytime I started looking at used Chevy Volts..

 

 

I think I posted something along those same lines when Chevy decided not to make the Volt E85 capable ...I wondered if it had anything to do with fuel (E85) sitting in the fuel tank for possibly months whle drivers stayed with in the 35 mile electric range

 

 

 

 

 

 

I was more concerned with the phase separation possibility..

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GIO..it's a question I have wondered about as well everytime I started looking at used Chevy Volts..

 

 

I think I posted something along those same lines when Chevy decided not to make the Volt E85 capable ...I wondered if it had anything to do with fuel (E85) sitting in the fuel tank for possibly months whle drivers stayed with in the 35 mile electric range

 

 

 

 

 

 

I was more concerned with the phase separation possibility..

 

A total non-issue with E85 in the tank Dan. Modern auto fuel systems are sealed AND E85 can absorb a ton more water than E10- thus taking nearly infinity to phase separate in a Volt tank. I also would park my 2wd S10 FFV for 5-6 months in the winter with E85 in it and it to this day still has the original fuel pump, composition sensor, fuel sender, and all other fuel components in it. Racer friends have stored E85 in sealed drums and 5 gal sealed plastic jugs for a year to insure full E85 summer blend so they do not affect carb settings- they do not leave it in open systems such as carbs and vented fuel cells however. The larger issue in the Volt is likely that the cold start cycles on E85 could have caused just a bit more emissions in that mode. The other issue is just that GM did not see a market clambering for E85 in such a fuel sipping car and would have just experienced more costs in emissions testing.

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GIO..it's a question I have wondered about as well everytime I started looking at used Chevy Volts..

 

 

I think I posted something along those same lines when Chevy decided not to make the Volt E85 capable ...I wondered if it had anything to do with fuel (E85) sitting in the fuel tank for possibly months whle drivers stayed with in the 35 mile electric range

 

 

 

 

 

 

I was more concerned with the phase separation possibility..

 

A total non-issue with E85 in the tank Dan. Modern auto fuel systems are sealed AND E85 can absorb a ton more water than E10- thus taking nearly infinity to phase separate in a Volt tank. I also would park my 2wd S10 FFV for 5-6 months in the winter with E85 in it and it to this day still has the original fuel pump, composition sensor, fuel sender, and all other fuel components in it. Racer friends have stored E85 in sealed drums and 5 gal sealed plastic jugs for a year to insure full E85 summer blend so they do not affect carb settings- they do not leave it in open systems such as carbs and vented fuel cells however. The larger issue in the Volt is likely that the cold start cycles on E85 could have caused just a bit more emissions in that mode. The other issue is just that GM did not see a market clambering for E85 in such a fuel sipping car and would have just experienced more costs in emissions testing.

 

 

Morning Phil..yeah that's what the "report" is also saying..simply not an issue .

 

 

I've seen 2 used Chevy Volts in $23,000-$26,000 range.. I do believe that  technology is where we are headed.. electric running around town.. liquid fuels for extended range.. between Electric and Ethanol and domestic oil/gasoline ..no reason we cant be totally self sufficient within 20 years .

 

 

 

 

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I love the concept of a Volt, but with ND/MN winters and temps around zero, that gas engine is still going to run whether you have a hybrid or a Volt.

 

Winter driving is miserable enough with 4wd/awd. I can't imagine getting around with a car. (Maybe I'm spoiled.)  ;D

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