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183 comments on Countdown to $200 oil (3) - no gas tax needed...erm, right...
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Hi kdolliso,
PUD: He is blandly asserting that one gallon of ethanol exactly replaces one gallon of gasoline, which is Just Plain Wrong...
k: I don't do Anything blandly.
Calorific values at this link. You need to use the lower calorific value, i.e. with water remaining as vapor, to get the heat available to an internal combustion cycle (you're welcome). Multiply by density to get volumetric energy density. Strictly speaking you should adjust to exhaust temperature, but that's not going to make much difference. I don't know the mixing volume loss for gasoline/ethanol blends - anyone?
http://en.wikipedia.org/wiki/Calorific_value#Lower_heating_value_for_som...
Ethanol=28.9, Gasoline=44.4 MJ/kg
I'd be interested in your comments. Hint: "irrelevant" won't cut it. As SwordsOfDamocles says (paraphrasing), there's probably a lot of efficiency improvement to be made in mass-market IC engines, irrespective of fuel type, but those numbers aren't going to change.
Two questions. Is the electricity that is included in the 17.7kBTU energy input that you quote fully-burdened with generation cycle efficiency?
And, just out of curiosity - as a teenager, did you get whacked upside the head with a copy of Atlas Shrugged?
Cheers,
PUD
Hey, PUD
Read it when I was young; don't remember much about it.
I'm just interested in the "Real" World. BTUs don't mean a thang if you can't get the energy out. In the Real World you need Octane. Ethanol has gobs of it. 113 - 116, depending on how you measure.
Throw some compression to it, and you can knock gasoline's socks off. At low to medium blends you don't need too much compression to equal gasoline's performance. Two Links: First one on "Efficiency," Second on on EPA cycle test using midlevel blends.
http://www.methanol.org/pdf/ISAF-XV-EPA.pdf
http://www.mda.state.mn.us/news/publications/renewable/ethanol/e20drivab...
Again, a Hershy Bar has a thousand btus, or so; but you can't burn it in an ICE. BTUs, without considering Octane, is a worthless metric. In the "Real" world you can do as much work with ethanol as with gasoline.
Octane number, and therefore compression ratio, certainly affects thermodynamic efficiency, but if you aren't putting the energy in you aren't going to get it out. So ethanol is starting off at a disadvantage.
(Idle speculation) I bet you could dissolve Hershey Bars in fuel oil and run 'em through a Wartsila-Sulzer RTA-96. Which the manufacturer claims to be the most efficient non-combined-cycle prime mover ever made (almost 50%). Would probably need a total rebuild afterwards though. And it wouldn't fit in a car - 1820 litres per cylinder, up to 14 cylinders.
PUD.
PUD,
To support your argument, I have said elsewhere on this post that the compression ratio/efficiency curve is pretty flat by the time 10:1 is reached. At 10:1 its about 60%, at 14:1 its about 65%. The additional load on the piston rings and the shearing loss in the oil film of the crankshaft bearings, imposed by the the additional load, mean some of this thermal efficiency gain is lost through increased friction. No amount of compression ratio increase will make up for the reduced calorific value of ethanol, period.