Converting From Conventional Gasoline To E10

By Kevin Hughes

Ethanol is added to gasoline to produce gasohol, or E10, which is ideally 10 percent ethanol and 90 percent gasoline. All conventional vehicles can burn E10 with no issues. Another ethanol-gasoline blend is E85, which has seasonal and geographic blends. During the winter months, E85 will contain more gasoline: up to 70 percent ethanol and 30 percent gasoline. However, in the summer months, the E85 blend becomes closer to the 85 percent ethanol and 15 percent gasoline that the term E85 indicates. Only certain vehicles, such as flex-fuel vehicles, can burn E85.

Scouring
When converting to ethanol-blended fuels, it would be ideal to start with a new tank, new pipes and a new dispenser. If this is not practical, then the tank, lines and dispensers need to be carefully cleaned of buildup. Although it is likely that the equipment is compatible with ethanol-blended fuels, it is a good idea to check and verify this with the manufacturer.

The issue with old equipment is scouring. Ethanol is a very aggressive solvent that will dissolve gums and varnishes that have built up in the tank and cause them to flake off. These particulates can then move downstream where they clog filters and fuel components. When converting an existing tank, lines or dispensers, it should be expected to have the filters clog frequently. Depending on how much material is scoured, the filters may need to be changed within 24 hours of startup.

Water and Phase Separation
Water is the enemy when it comes to ethanol-blended fuels. Ethanol and water are infinitely soluble in one another. When water first enters the mix, the ethanol has no problem holding on to the water, but a little bit more water and the ethanol-water mix dissociates from the gasoline and settles to the bottom of the tank as an unburnable phase, commonly termed phase separation. In addition to the ethanol-water settling to the bottom comes changes in the petrochemistry. When the ethanol falls to the bottom of the tank, it takes some ethanol-soluble hydrocarbons with it, leaving mainly paraffinic hydrocarbons in the gasoline rich phase.

Many variables impact the risk of phase separation, and we will consider each in turn. Phase separation is a function of temperature; the lower the temperature, the less water the ethanol can hold and still tolerate the gasoline. The percentage by volume of water is extremely low, being roughly 0.2 percent to 0.7 percent for most temperature conditions experienced at most locations.

One thing to consider with underground storage tanks is the temperature difference between the ambient ground temperature and the ambient air temperature. In most conventional settings, the ground temperature will be cooler than the air temperature in the summer and warmer than the air temperature in the winter. If phase separation has occurred in a storage tank in summer and bad fuel (gasoline with emulsified phase-separated ethanol) is pumped into a vehicle, the warmer vehicle fuel tank may cause the phase-separated ethanol to remix with the fuel. This is, however, dependent upon several variables such as water content in the fuel. On the other side, if fuel in a storage tank that contains some moisture in the winter but not enough to cause phase separation is pumped into a vehicle, the colder vehicle fuel tank can put the fuel over the phase separation threshold. What this means is that although the fuel in the storage tank is fine, the fuel in the vehicle goes through phase separation.

Another factor that contributes to phase separation is the exact ethanol content of the fuel. In general, the larger the volume of ethanol, the more water it takes to cause phase separation. This means that E10 will experience phase separation with much less water than E85. One thing to consider with this is the inexact nature of the ethanol-gasoline mixing process. This means that E10 may actually be 8 percent, 12 percent or some other percentage of ethanol. Studies done by Central Illinois Manufacturing have found that E10 can actually be as low as 5 percent ethanol and as high as 13 percent ethanol. These have been exceptions; the more nominal values have been within 9 percent to 11 percent. In other words, E10 may actually be E8, and if it is E8, it will take less water to cause phase separation than if it was actually E10. Some scientific studies have suggested that as a tank is emptied over time, the concentration of ethanol in the fuel will decrease due to differential evaporation. This means that even if the water content of the tank remains constant, the loss of ethanol can cause phase separation to occur as the tank empties.

One last thing to consider about phase separation is water accumulation. Water tends to accumulate in the bottom of tanks, and it is difficult to remove all the water from the tank bottom. When a fresh dump of E10 is introduced into the tank, the bottom layer can be disturbed and mixed with the new fuel, causing phase separation to occur in the fresh load. Another event can cause this bottom layer to mix into the overlying fuel layer. That event is an earthquake. Therefore, keep the tank bottom as free of water as possible.

How Water Enters the Tank
Water can enter a tank through several means. Loose fill caps, leaky fittings and faulty gaskets are all entry points for water. Water can accumulate around the fill gauge manhole or in the secondary containment submersible pump pit. A leak in the tank or the lines will allow moisture to enter the tank; this is especially true of underground storage tanks. Every time the tank is open, there is a potential for water to enter.

Conversion Guide
When switching from gasoline to ethanol-blended fuels, use a new installation if possible. If not, clean the tank, lines and dispensers as thoroughly as possible. Use a high-performance dispenser filter with a large dirt-holding capacity to catch material that the ethanol might scour into the fuel. Make sure to pump as much water as possible out of the bottom of the tank. Then the remaining water that cannot be removed can be treated with a chemical that makes the water unavailable to participate in a phase separation reaction.

You must check all gaskets and fittings and ensure that they are water tight. You want to keep the tank moisture-free from the time the tank is cleaned to the time the first load of ethanol fuel is delivered. It is then imperative to keep moisture out of the tank the whole time ethanol fuel is in use.

After first delivery, check the tank several times for water for the first 48 hours and then daily thereafter. Flush the dispenser lines until the product comes out clear. Please note that if phase separation occurs, then the fuel will come out milky looking. This could be the result of condensation in the line between the time of the first dump and the cleaning of the tank. Keep flushing until the product is clear. If the product never becomes clear, then double check to see if moisture is in the tank.

While using an ethanol-blended fuel, an alcohol monitor should be used. Alcohol monitors are filters with ethanol water phase-detecting media. Upon contact with phase-separated ethanol, these filters reduce flow. The flow reduction can alert the gas station attendant to a problem and prevent bad fuel from entering a customer tank.

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The PEI Journal • First Quarter 2009 • Volume 3, No. 1 • Contents are Copyright © Data Key Communications, Inc.
All rights reserved. • Nothing may be reproduced in whole or part without written permission of the publisher.