Gas mileage of ethanol-added gasoline?

[ab1ga]

I trust the numbers in Paul's original post, and I agree with the immediate results of his calculations, but I disagree with some of his interpretive statements.

Based on his numbers, to travel 300 miles not only requires more hydrocarbon/ethanol fuel blend, but actually more of the hydrocarbon component as well.

The first part is not surprising: since the energy density per liter of ethanol burning to CO2 and water is lower than the volumetric energy density of hydrocarbon fuels, any blend must have less bang per volume of fuel.

The second part is more interesting, since not only is the ethanol a less efficient fuel, but it makes the hydrocarbon it's mixed with less fuel efficient, "wasting" fuel and contributing to global warming, because the excess hydrocarbon fuel used is NOT carbon neutral. Why would anybody cheese off both the left and the right wing by mandating ethanol use? Corruption? Bureaucratic stupidity?

Try science and environmental policy from before the climate change and energy supply issues took center stage.

The requirement to add ethanol to automotive fuel was instituted to change the chemistry in the combustion chamber, predominantly by introducing additional oxygen, in order to minimize the generation of precursors of photochemical smog.

The addition of ethanol was driven by clean air concerns, not fuel efficiency or climate change arguments, and based on personal experience it has in fact worked. One can reduce dependency on foreign oil and CO2 emitted by automobiles, but are we willing to go back to the days of the brown clouds? It's an unpleasant trade-off to consider, but it isn't going away without major changes in transportation technology and practices.

[N2RJ]

Unless the rubber has been treated to tolerate that. Aircraft rubber parts are treated to resist the MEK we need to use to clean parts; and resist the acidity of Triple Nickel oils.

They do to a point but using alcohol free gasoline will still make them last longer.

Cars designed to withstand ethanol usually don't have much rubber parts that touch the fuel and have stainless steel plastic lined hoses.

[rot]

I trust the numbers in Paul's original post, and I agree with the immediate results of his calculations, but I disagree with some of his interpretive statements.

Based on his numbers, to travel 300 miles not only requires more hydrocarbon/ethanol fuel blend, but actually more of the hydrocarbon component as well.

The first part is not surprising: since the energy density per liter of ethanol burning to CO2 and water is lower than the volumetric energy density of hydrocarbon fuels, any blend must have less bang per volume of fuel.

The second part is more interesting, since not only is the ethanol a less efficient fuel, but it makes the hydrocarbon it's mixed with less fuel efficient, "wasting" fuel and contributing to global warming, because the excess hydrocarbon fuel used is NOT carbon neutral. Why would anybody cheese off both the left and the right wing by mandating ethanol use? Corruption? Bureaucratic stupidity?

Try science and environmental policy from before the climate change and energy supply issues took center stage.

The requirement to add ethanol to automotive fuel was instituted to change the chemistry in the combustion chamber, predominantly by introducing additional oxygen, in order to minimize the generation of precursors of photochemical smog.

The addition of ethanol was driven by clean air concerns, not fuel efficiency or climate change arguments, and based on personal experience it has in fact worked. One can reduce dependency on foreign oil and CO2 emitted by automobiles, but are we willing to go back to the days of the brown clouds? It's an unpleasant trade-off to consider, but it isn't going away without major changes in transportation technology and practices.

You agree that the enthalpy and stoichiometry of burn is the same for dodecane as is for octane?
rot

[ab1ga]

You agree that the enthalpy and stoichiometry of burn is the same for dodecane as is for octane?
rot

Goodness no, I didn't use those numbers because I didn't need them, and at the very least they contain a hell of a typo or transcription error. Paul's original post with the mileage for both blended HC-only fuels was all I used, and other posts in the thread seemed to verify the phenomenon, if only qualitatively.

Since petroleum based fuels are quite variable in composition by source and seasonal changes in blending, I feel using tabular thermodynamic data of pure compounds can lead to errors in interpretation similar to those resulting from belief in false precision. I am not even sure of the range of compounds and their molecular weights for automotive fuels. Dodecane sounds more like a component of diesel fuel than gasoline, but I wouldn't be surprised if it were a minor component of automotive fuel.

One place where I did take liberties was the use of volumetric calculations rather than gravimetric ones when assessing the proportion of the blend which was ethanol and which was HC. Volume is not conserved upon mixing, but I wouldn't expect a large error and it would have been in a direction which wouldn't have changed the nature of the result.

Again, that the blend is less fuel efficient is not surprising, but the 15% increase in the consumption of HC fuel in addition to the ethanol had me scratching my head. My first guess is that the pollution mitigation comes from reductions in combustion chamber temperature. Carnot engine efficiency goes as (Tchamber - Texhaust)/Tchamber, if I remember correctly, and is the theoretical maximum heat engine efficiency. In a real car engine, the lower Tchamber would cause less torque, requiring more rotational speed to maintain output power. I ain't no automotive engineer, so your mileage may NOT vary.

But the point of my post was really that ethanol was never intended to make fuel go further, but to reduce pollution. The ethanol provides oxygen in addition to the mixed atmospheric air, which in turn reduces unburned hydrocarbons. The lower combustion temperature lowers NOx production, which if I remember my chemistry correctly react to form smog when photochemically triggered. Sadly, policy makers have forgotten the reason for adding ethanol in the first place, and falsely assumed it was used purely as a substitute for hydrocarbon fuels. The backlash of fuzzy ethanol policies now threatens to reverse decades of gains in air quality, which I feel would be a terrible shame.

73,

[ka4dpo]

I just bought a new truck last week and it has a Flex Fuel engine, that means it can use E85 or any Ethanol blend. It says right in the owners manual that power and mileage will be less with Ethanol blended fuels. That's no secret, not for a long time. AB1GA is right, the purpose is to reduce pollution but the truly amazing thing is that modern engine control systems are adaptive enough to even allow a car to run on such a diverse mix of fuel.

[N2RJ]

but the truly amazing thing is that modern engine control systems are adaptive enough to even allow a car to run on such a diverse mix of fuel.

Nah, not really amazing. They just use more expensive materials like stainless steel to prevent gas tanks from being corroded and lower our expectations about how long the car will last and run properly.

[N1LAF]

Dale is right when it comes to the reasoning of ethanol, but like many good intentions, there are secondary effects that not seemed to be considered. I was reading one of those secondary effects, where the production of soybean decreased to make more room to grow corn (for ethanol), Brazil, increased soybean production, and was clearing the forest to do so. It is interesting with the trade-off issue, one is to use food products for fuel, and we no longer hear those commercials dealing with world hunger as we did in the past.

This is the kind of discussions I miss, being in the forum world of cut & burn. We should have more discussions like this (big thanks to Dale and Rot...)

[rot]

Well maybe I is a doofus here, but I only see references sited from 2 places...the Energy in America article and the Intota whatever... I am not sure what Paul's original post points to (thought that was the dodecane one) but so be it.
and I just lost my rant in the fine boardbuffering so you got spared on that one..
Anyhoo maybe some other time gents..have a fine day!
Early morning rot to ya!
(p.s. "rot to ya" is not meant to be interpreted as an "up yours" or anything like that for the record)
Noflame,NC
rot

[N1LAF]

Rot, your informative and insightful posts are most welcome. If you see an error, by all means jump right in. My point is that if the same volume of fuel for each type releases the same amount of CO2, the non-ethanol brand, having more energy capacity, will release less CO2 than the ethanol blend.

[ka4dpo]

Nah, not really amazing. They just use more expensive materials like stainless steel to prevent gas tanks from being corroded and lower our expectations about how long the car will last and run properly.

I suppose it depends on how old you are. I raced motorcycles as a yong man and it took a lot of carburation and ignition timing changes to get a gasoline engine to run on alchohol. Of course mine were tuned in a way that produced significantly more horsepower than with gasoline but I also ran a 15:1 compression ratio. Having been modified to run on alky however, they would not run on gasoline at all.

In the 1980's automobiles were dismal creatures barely able to run on the new unleadded gasoline. Even with a compression ratio of 9:1 they had a tendency to knock when hot and horsepower was pathetic. At some point in the early 90's the Japanese, Honda primarily, invented a working knock sensor and a computer system that could retard and advance the timing in milliseconds. Compression ratios began to climb and so did power. Now most high output cars run 11 to 11.5:1 and can produce well over 300 horsepower with a small six cylider engine. Turbo charged and super charged small blocks are in 600 HP territory, and on unleaded gas. It wasn't that long ago that was beyond imagination.

It takes a lot of sophisticated technology to produce engines that can run on a wide range of fuels. Stainless tanks and fuel resistant rubber are the easy parts. Getting an engine to run reliably on gasoline, alchohol, or a mixture of both is a modern miracle if you are old enough to remember when to do so was impossible.