You're taking a bunch of `C` in the tank (AMU: 12) and 2x `O` out of the atmosphere (AMU: 16). This means the expected mass goes from 12 -> 44, or an increase of 3.6. My trusty calculator says that takes .71kg to 2.6kg.
This is just approximate, since fuel has a bunch of H and S and other crap, so it's not 100% C. But, yes, these figures are in the right ballpark.
You are correct of course. I was intending to make an alchemy joke about a particular phrasing of the parent poster (the part about creating 1 tons of "carbon"), but misread the entire message and commented on the wrong part. :-/
Meanwhile the hydrogen in a hydrocarbon is somewhere in the range of 1/7th of the weight, so the fact that it all goes up the exhaust pipe in the form of water doesn't really subtract all that much weight from the input.
There's more energy in the hydrogen bonds, not the carbon-carbon bonds, right? Just adds insult to injury, if you ask me.
On the surface, it seems like you're only burning fuel in an engine. People forget, or may not even know that you're burning mostly air, and the fuel is there to help burn the air. I think this was a legit question to ask, as it's going to be a common misunderstanding for a lot of people.
This is just approximate, since fuel has a bunch of H and S and other crap, so it's not 100% C. But, yes, these figures are in the right ballpark.