On one hand, this doesn't seem like a lot - at least it's fairly insignificant compared to what the average North American puts into her car. The average commuter might reasonably burn 10 times as much gasoline than this in her car each week. On the other hand, when you think about how much heavier and therefore harder to move cars are than people, 33km is looking pretty good. It's clear that cars are making much better use of fossil fuels than humans are. So maybe we should stop "eating" fossil fuel energy and just feed it to our cars and other machines. That would make living difficult though, wouldn't it? And besides, aren't the machines just there to make life better/easier for us in the first place?
(Follow-up Bayblab bonus homework: With the manufacturing processes in use right now, how much ethanol fuel can you get out of the grain in a box of 2kg cereal? How far could you drive that 2008 Honda civic on this ethanol? How much additional fossil fuel input is needed to convert the cereal grain into ethanol? How far could you drive a Honda civic on that extra fossil fuel?)
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According to this site:
http://www.inra.fr/productions-animales/spip.php?page=en-article&id_article=190
In white oats (probably most of that cereal box) has an apparent metabolizable energy (AME) value of 2879 kcal/kg (which is 5758 kcal/box).
That's about 24 MJ/box.
Assuming that the AME index is about what a yeast would be able to metabolize out of the cereal, and that the ethanol was as efficiently burned as possible (both bad assumptions, but I'm running with them), then:
Wikipedia says that 1 Litre of alcohol fuel is about 21.1 MJ. So you'd be getting a little over a litre of ethanol from a 2kg box of cereal.
Does that make sense? Dunno, I'll check the numbers once I've had coffee...
These guys have some interesting numbers:
http://www.ncga.com/ethanol/pdfs/2007/HowMuchEthanolCanComeFromCorn0207.pdf
One says that current manufacturing gets about 2.8 gallons / bushel of corn.
A bushel is about 25kg corn/wheat so that's 0.42 L/kg grain, or 0.84 L from a 2kg box of cereal.
Pretty close to your theoretical calculation of just over 1L doc. I guess it suggests that the conversion of grain to ethanol energy is a bit less than 84% efficient?
So this means that using industrial agriculture, it takes 1.9 L of gasoline to make 0.84L of ethanol fuel. This is before even factoring in the fossil fuel cost of converting the grain to ethanol, which is going to be pretty significant I would guess.
Strictly speaking, I'm a physical chemist, so I guess I'd have been disappointed to find out that I was really out.
Of course, we don't know how much gas it takes to make a gallon of gas. By that, I mean something has to pump, and move, and heat, and shift around all that oil... that's all gotta come from somewhere.
Also, I suspect that there is a big difference from WHERE that ethanol comes from - corn is not oats (which is what my calculation was based on). That original site I link to outlines the AME for corn, I think.
That's also not to mention the differences in forms of Agriculture. I recall that agriculture in NZ uses much less petrol and produces a much lower amount of CO2 because we have fewer pests and better soil - which means less spraying and watering. Even taking into account the shipping costs of getting the food to N. America/Europe, it works out that NZ's food has less CO2 waste than local farming (if I remember rightly).
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