Fossil fuels are called hydrocarbons because they are in dominance composed by Carbon and Hydrogen.

When a  fossil fuel has the right conditions of temperature and pressure can be oxydated by the oxygen so the CH chemical link can break down in water H2O and CO2. That happens naturally in case of an ideal combustion, a real combustion has particles like Nitorgen Oxydated (NOx), fuels unburned (HC), Sulfure oxydes (SO, SO2,...)  

The combustion is prepared with the mass of fuel in ratio with the air: stechiometric ratio (lean combustion, oxygen is just enough to burn the overall) or air excess ratio. Air gets heated during the compbustion hence his volume increases: the heat can than be transformed in work.

The heat can be used as it is for processes where there is no need to work trasnformation:

syderurgy to produce iron and alloys, cement, tiles, glass, ....

The heat can be transformed in work when there is teh need of mechanical energy: combustion engines (diesel, gasoline, gas, hydraulic pomps, steam turbine).

The mechanical energy can be transformed in electricity: by using generators ....

Here after a list of the most common fuel used to produce heat that.


 Fossils commonly used vs Hydrogen




Status at ambient conditions

LHV (Low Heat Value)


 g of CO2 / MJ g of H2O / MJ

GHG index as fuel

 hard black Coal  C  solid  34 94.6 0   low
 Methan (SMC @ 15C)  CH4  gas  50 55 45  high
 Ethan  C2H6  gas 47.62       low
 Propane  C3H8 gas 46.35       low
 Gasoline  from C6H14 to C8H18  liquid ~45  69.3    low
 Diesel from C13H28 to C18H38 most frequent C16H34 (paraffinic, naphthenic, or aromatic class)   liquid 43.4   74.1     low
  Hydrogen  H2   119.96  0  2547  null


When using a fossil fuel we need to evaluate four main points:

  1. the amount of CO2 eq / MJ
  2. the amount of H2O / MJ
  3. the risk of Green House Gas effect of the fuel itself if leaked in the athmosphere
  4. The natural tendency of the fuel to have a clean combustion


Hydrogen is the combustible that doesn't have any CO2 emission at the combustion, naturally its production has to be green: not produced with processes underlining processes that prodcue CO2.

Methane has a low CO2 emission but the leakage in athmosphere of 1 molecole of CH4 values ~ 40 molecoles of CO2