Hydrocarbons have very similar energy/mole and therefore energy/volume, energy/mass ratios. This relationship breaks down for very short HC (methane, basic alc

Hydrocarbons have very similar energy/mole and therefore energy/volume, energy/mass ratios. This relationship breaks down for very short HC (methane, basic alcohols). Differences in effective energy density result from the combustion cycle used: Otto is better than Diesel for the same compression ratio, but you can’t easily get high compression ratio