charcoal 29.0 MJ/kg
diesel 45.3 MJ/kg
(from
http://hypertextbook.com/physics/mat...ergy-chemical/)
("energy density" is a good search term here)
So diesel fuel provides about 1.5 times as much energy per kg.
Also, diesel has a density of 0.85 kg/l. Combining this gives
1 kg charcoal
= 29.0 MJ
= (29/45.3) = 0.65 kg of diesel
= 0.65kg / 0.85kg/l = 0.77 liters of diesel