We love them, we hate them, we've created a society which is totally dependent on them and we can't live without them: the internal combustion engine. Even if we don't drive we're stuck with them. They'll be with us a while yet, and they'll likely always have a part to play, so it's worth reviewing the ICE, specifically the piston engine ICE, comparing gasoline and diesel with an eye to efficiency.
The ICE is a prime mover, it converts an energy source into power. It is my hope that eventually the vehicle distribution will be largely electric (and that there will be far fewer of them): the electric motor in that case will not necessarily qualify as a prime mover, since something has to charge the battery (EVs using fuel cells taking methane or liquid fuel would be an exception). This has implications when comparing relative efficiencies. But I'll talk about EVs another day.
It's a bit long, so if you don't want to read the whole thing, here's the upshot: if you're trying to get the most performance out of a given engine displacement, use gasoline. If you're trying to get the most performance out of a given volume of fuel, use diesel.
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