If ethanol (E85) is suppose to have a higher octane rating why does it get less mpg?

Question

If ethanol (E85) is suppose to have a higher octane rating why does it get less mpg?

Answer 1

The octane rating is a scale of how well a material burns in an internal combustion engine. The scale is defined with 0 as heptane and 100 as an isomer of octane (2,2,4 trimethylpentane or something like that if I remember correctly). It has absolutely nothing to do with the amount of energy you get out of a gallon and thus the mpg rating. For example, diesel has a large energy density (which is why I get 45+ mpg in my diesel Jetta) but would not burn well in a gasoline engine. As a result it would have a very low octane rating.

Answer 2

Pure ethanol has a very high octane rating.

E85 is normal octane because they make it to be like gasoline.

About the MPG:

Gasoline has 120,000 BTUs of energy per gallon.

Ethanol has 70,000 BTUs of energy per gallon.

With this lack of energy, you get less MPG.

Answer 3

everyone is hitting around the mark. octane rating only tells how a fuel operates in the combustion chamber regarding its ability to prevent detonation. the higher the octane rating of gasoline, and other fuels, means you can run higher compression ratios, more ignition lead, and leaner fuel mixtures before you get detonation. detonation is the uncontrolled burning of the fuel mixture in the combustion chamber.

alcohol(both ethanol and methanol), propane, methane, and other fuels have higher octane ratings than gasoline, they also have less BTU energy than gasoline. this mean that you have to run more if it to produce the same power as gasoline, up to twice as much. since you are running more fuel through the combustion process, you get lower fuel economy, because you have a higher brake specific fuel consumption(bsfc). the only motor fuel that has a higher BTU content than gasoline is diesel fuel, and kerosene. however these fuels are much harder to light off than gasoline, and require higher temperatures to ignite them, thus you cant run diesel through a gas engine, except in small amounts, less than 5%.

Answer 4

The energy content of ethanol is about 30-35% less (per volume) than gasoline, so an E85 fueled vehicle will use about 30-35% more E85 (85% ethanol fuel / 15% gasoline) compared to 'straight' gasoline to do the same amount of work.

As an example, a flex-fuel Chrysler Sebring gets 19/27 (city/highway) with gasoline, and 13/20 (city/highway) with E85.

The Chevy Impala gets 18/28 with gas, and 13/20 with E85.

If you're unfortunate enough to own a flex-fuel Dodge Dakota pickup, it gets 14/19 with gas, but only 9/12 with E85.

Answer 5

Corn ethanol sucks, it's expensive, not environmentally friendly, and is 27% less efficient that regular unleaded.

Answer 6

to put it simply because ethanol has less energy per gallon than gasoline

you burn ethanol faster and refuel more often

(E10) 10% ethanol 90% gasoline has better fuel octane than (E85)

ethanol is not the solution to energy independence for the u.s however it was for brazil who is claiming to become 100% energy independent.

most people dont know that ethanol is made from a majority of non renewable energy like coal and fossil fuels

its made from only 26% renewable energy from solar by the corn and nuclear renewables