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E15 Fuel Warning / Flex Fuel Vehicles

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In the last few days I've posted a bunch of info on stoichiometric air/fuel ratio and octane rating. I wanted to post up that info first because it is very important when talking about the new ethanol based fuels like E15, E85, and E100.


Cobie sent me the video link below earlier this week and wanted my take on it. It has to do with some of the new ethanol based fuels(specifically E15) and what affect it can have on using it in an older motor that was not designed to run it.



More corrosive

The first major point that Lauren Fix makes in the video talks about how ethanol(alcohol) based fuels are more corrosive than regular gasoline. This is indeed true from everything that I have heard and read. Vehicles that are designed to run regular gasoline typically have fuel line parts that are made of rubber. Running a fuel with a higher ethanol content will corrode these parts more quickly. I don't have any concrete data on exactly how bad or how quickly. Dragster guys that run alcohol fuel will typically use metal fuel line components which are more corrosion resistant.


Octane Rating

From my post about octane rating we know that E100(pure ethanol) has a higher octane rating than gasoline(108-113 octane vs. 92-95 octane). So if gas companies add MORE ethanol to raise the octane in the ethanol/gasoline blend, they can use a gasoline that has a lower octane rating. Lauren talks about this in the video and goes on to talk about how the ethanol and gasoline can separate in your tank. Ethanol and gasoline have different densities, so this is possible. If the gas separates from the ethanol and ONLY the lower octane gas is being delivered to the motor, it could cause it to knock.


Air/Fuel Ratio

Another thing to consider with using more ethanol in an ethanol/gas blend is the effect it has on the air/fuel ratio. Ethanol has a much lower stoichiometric air/fuel ratio than gasoline(9:1 vs. 14.7:1). If you add more ethanol you are going to LOWER the stoichiometric air/fuel ratio of your fuel. Lowering the stoichiometric air/fuel ratio requires that MORE fuel be delivered to the motor to maintain the same air/fuel ratio. So your motor will now be running LEANER if it is delivering the same amount of fuel.


The oxygen sensor on your vehicle will be able to detect the change in air/fuel ratio in some areas and will add more fuel to make it richer again, but the motor will be running LEANER in the areas where the oxygen sensor is not used. The areas where the oxygen sensor is not used are typically the high throttle, high RPM areas. I wouldn't want my motor running leaner there! :/


Flex Fuel Vehicles

The new "flex fuel" vehicles have fuel system components that can handle the more corrosive ethanol. They also have engine management systems with sensors that can detect the ethanol content of the fuel. Since it can detect how much ethanol is in the fuel, it can automatically adjust the amount of fuel that is needed to get the motor to run properly.


Interesting Cost Point

Part of the appeal of running the ethanol blend fuels like E15 and E85 is they are listed as being a cheaper price per gallon. But because the stoichiometric air/fuel ratio of alcohol is much lower than gasoline you have to run more of it. It's true that you will be paying a cheaper price per gallon, but you are going to have to buy MORE gallons. You're MPG will actually go DOWN running more ethanol!


Hope that all makes sense. There is a lot of data there. Please fire away with any questions.

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