The approximate energy density of diesel fuel is 38.6 megajoules per liter. This is a volumetric energy figure, describing how much chemical energy is contained in a liter of fuel.
Diesel’s relatively high energy density helps explain why diesel engines can deliver strong driving range and pulling power with modest fuel volumes. The number is normally presented as an approximate lower-heating-value figure, not as a guaranteed amount available as useful mechanical work at the wheels.
Actual values vary with fuel formulation, temperature, density, and whether the fuel is conventional petroleum diesel or a blend containing biodiesel. Biodiesel generally has a lower energy density than petroleum diesel, so a higher biodiesel percentage can slightly reduce energy per liter. Energy density is also different from octane or cetane rating: cetane describes ignition quality, while energy density concerns the fuel’s stored chemical energy.