# Heat Contents of Fuels

 Fuels: The energy available   wood, oil, gas coal methane hydrogen  Note!==> Units and equations are nice, but rather meaningless without any numbers to go into them. In this section, I give a few very approximate values for various sources of energy and for various uses.  The Heat Content table shows the heat that is released when various fuels are burned. By "wood," I refer to most wood (ash, oak, pine ...). A log of oak releases more heat than one of pine simply because it is heavier, not because the wood is different. Similarly, a kilogram of petroleum --- whether it be gasoline, diesel fuel, or crude oil --- releases the same amount of heat. However, crude oil is somewhat denser, so a bucketful of crude oil will release more heat than a bucketful of gasoline.  Coal always contains mineral impurities. Very poor coal has about 50% impurities, so when you "burn" a kilogram of very poor coal, you are really burning about a half kilogram of "real" coal; the rest is merely weight that becomes ash.  Methane is the major component of natural gas.  There is no natural supply of hydrogen, but hydrogen could be a manufactured fuel, made by removing it from water. It takes a lot of energy to do so, of course, but at least the hydrogen can be transported.

#### MJ/kg (mega-joules per kilogram)

Wood (dry)
15
Coal (poor)
15 =1 ´ wood
Ethanol (EtOH)
30 = 1.8 ´ wood (*)
27 = 2 ´ wood
Petroleum
45 = 3 ´ wood
Methane
54 = 3.4 ´ wood
Hydrogen
140 = 8.8 ´ wood
Uranium (if all used)
80,000,000 = 5,300,000 ´ wood
(*)  It takes 46 MJ of energy to produce a kilogram of EtOH from corn!