how efficient is alcohol in the internal combustion engine?

Answer 1

Ethyl alcohol (ethanol or grain alcohol) has a very high (R+M)/2 octane rating. of (129 + 102) = 115. It will burn fine in an engine designed to run it. No special materials like ceramic are needed. Formula 1 cars and Indy cars burn alcohol and are made from the same materials your engine has in them today! E85 is a mixture of 85% alcohol and 15% gasoline. With such high octane rated fuels to get the most out of them you need to raise the compression ratio, tweak the valve timing (cam) etc. Flex fuel vehicles have a sensor that tells the computer what the exact ratio of alcohol to gas is so it can vary engine parameters (spark, fuel mix, etc.) accordingly.

What is different about alcohol than gas is that per gallon it has less energy. Gasoline has about 115,000 btu per gallon; ethanol has only 84,000 btu per gallon so you have to burn more of it to get the same effect as one gallon of gasoline. That means you have to tweak fuel injectors to spray more of it per cycle than gasoline. Carburetors will have to be rejetted to bigger sized jets to allow more alcohol to pass.

One alcohol, butonol is very close to gasoline and gives nearly the same btu/gal rating (110,000). BP and DuPont are teaming up to make this stuff in mass; right now it costs about $3.70 a gallon, which isn't far from what I pay for 93 for my supercharged Mustang GT! Mass manufacturing it for fuel could easily lower it price and make us totally independent of oil!

Now as far as how efficient the engine is, the last link I put in place shows a 9% increase in miles per gallon from using butonol in an unmodified car. However, to get the best bang for the buck on that stuff, you'd need to raise the compression and tweak the valve timing (easily done on cars with electronic valve timing control; aka VTEC from Honda) to get more out of the fuel. Superchargers and turbos could be used as well to boost engine output safely with such a fuel.

Butonol has an (R+M)/2 rating that is about 25% higher than gasoline putting it at about 108 versus 87!!! The last time I saw a 108 on a gas pump was at a NASCAR event or when I was a small kid in the 60's at a Sunoco station!!! A good high performance engine would LOVE the stuff!! My supercharged Mustang could probably run a lot more boost with this stuff!!

Answer 2

Alcohol is considered a renewable resource, whereas the crude oil that gasoline is derived from will eventually run out. Also, alcohol can be distilled anywhere there are grains, corns, etc, whereas crude oil is generally more concentrated to certain regions of the the world.

On the downside, I don't know how efficient the net process of distilling alcohol would be. It is a very interesting discussion with gas prices hovering at US$3/gallon. I just saw a news report that moonshiners have been given permission to sell stills as long as the distilled alcohol is ONLY used for fuel. I thought it was about 200 proof and not exactly something anyone with intellegence would consume anyway!

Answer 3

Alcohol has a higher octane value than available gasoline. This doesn't make any difference to an ordinary car, but an engine designed for alcohol can use a higher compression ratio and therefore be more efficient, in terms of percent of available energy utilized. Alcohol has a lower energy density than gasoline, so you have to burn more of it for a given amount of power. Therefore its efficiency in terms of miles per gallon will be lower.

Answer 4

It's actually pretty good. It's octane rating is 106 I think. Higher than the gas you're burning now. You'll get more power from your engine. The only downside it that it's difficult to start an engine on ethanol when it's cold.

Answer 5

wires answer is correct. the downside to ethanol as fuel (and why they mix it with regular gas) is that it burns at higher temperature. In theory, you could run a regular gas engine on pure ethanol, but it would soon over-heat, start to melt, and seize up! Engines will need to be redesigned (perhaps using ceramic or ceramic-composite materials) for alcohol to be truly practical.

Answer 6

I can't imagine alcohol being less expensive than gas.