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Heat of combustion



 It has been suggested that Heating value be merged into this article or section. (Discuss)

The Heat of combustion (ΔHc0) is the energy released as heat when a compound undergoes complete combustion with oxygen. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat. It may be expressed with the quantities:

  • energy/mole of fuel
  • energy/mass of fuel
  • energy/volume of fuel

The heat of combustion is traditionally measured with a bomb calorimeter. It may also be calculated as the difference between the heat of formation (ΔfH0) of the products and reactants.

Contents

Heating value

The heat of combustion for fuels is expressed as the HHV (Higher Heating value) or LHV (Lower Heating Value).

Lower heating value treats any H2O formed as a vapor. The energy required to vaporize the water therefore is not realized as heat.

Higher Heating Value is the same as the thermodynamic heat of combustion since the enthalpy change for the reaction assumes a common temperature of the compounds before and after combustion, in which case the water produced by combustion is liquid.

Heat of combustion for common fuels (higher value)

Heat of Combustion
Fuel MJ/kg Mcal/kg BTU/lb
Hydrogen 141.9 33.9 61,000
Gasoline 47 11.3 20,400
Diesel 45 10.7 19,300
Ethanol 29.8 7.1 12,800
Propane 49.9 11.9 21,500
Butane 49.2 11.8 21,200
Wood 15 3.6 6,500
Coal 15-27 4.4 - 7.8 8,000 - 14,000
Natural Gas ~54 ~13 ~23,000

Lower heating value for some organic compounds (at 25°C)

Fuel MJ/kg kJ/L BTU/lb kJ/mol
Paraffins
Methane 50.009 --- --- ---
Ethane 47.794 --- --- ---
Propane 46.357 --- --- ---
Butane 45.752 --- --- ---
Pentane 45.357 72.455 --- ---
Hexane 44.752 68.34 --- ---
Heptane 44.566 64.68 --- ---
Octane 44.427 63.19 --- ---
Nonane 44.311 61.71 --- ---
Decane 44.240 --- --- ---
Undecane 44.194 --- --- ---
Dodecane 44.147 --- --- ---
Isoparaffins
Isobutane 45.613 --- --- ---
Isopentane 45.241 --- --- ---
2-Methylpentane 44.682 --- --- ---
2,3-Dimethylbutane 44.659 --- --- ---
2,3-Dimethylpentane 44.496 --- --- ---
2,2,4-Trimethylpentane 44.310 64.40 --- ---
Naphthenes
Cyclopentane 44.636 --- --- ---
Methylcyclopentane 44.636 --- --- ---
Cyclohexane 43.450 --- --- ---
Methylcyclohexane 43.380 --- --- ---
Monoolefins
Ethylene 47.195 --- --- ---
Propylene 45.799 --- --- ---
1-Butene 45.334 --- --- ---
cis-2-Butene 45.194 --- --- ---
trans-2-Butene 45.124 --- --- ---
Isobutene 45.055 --- --- ---
1-Pentene 45.031 --- --- ---
2-Methyl-1-pentene 44.799 --- --- ---
1-Hexene 44.426 --- --- ---
Diolefins
1,3-Butadiene 44.613 --- --- ---
Isoprene 44.078 64.73 --- ---
Nitrous derivated
Nitromethane 10.513 --- --- ---
Nitropropane 20.693 --- --- ---
Acetylenes
Acetylene 48.241 --- --- ---
Methylacetylene 46.194 --- --- ---
1-Butyne 45.590 --- --- ---
1-Pentyne 45.217 --- --- ---
Aromatics
Benzene 40.170 --- --- ---
Toluene 40.589 --- --- ---
o-Xylene 40.961 --- --- ---
m-Xylene 40.961 --- --- ---
p-Xylene 40.798 --- --- ---
Ethylbenzene 40.938 --- --- ---
1,2,4-Trimethylbenzene 40.984 --- --- ---
Propylbenzene 41.193 --- --- ---
Cumene 41.217 --- --- ---
Alcohols
Methanol 19.937 --- --- ---
Ethanol 28.865 --- --- ---
n-propanol 30.680 --- --- ---
Isopropanol 30.447 --- --- ---
n-Butanol 33.075 --- --- ---
Isobutanol 32.959 --- --- ---
Tertiobutanol 32.587 --- --- ---
n-Pentanol 34.727 --- --- ---
Ethers
Methoxymethane 28.703 --- --- ---
Ethoxyethane 33.867 --- --- ---
Propoxypropane 36.355 --- --- ---
Butoxybutane 37.798 --- --- ---
Aldehydes and ketones
Methanal 17.259 --- --- ---
Ethanal 24.156 --- --- ---
Propionaldehyde 28.889 --- --- ---
Butyraldehyde 31.610 --- --- ---
Acetone 28.548 --- --- ---
Other species
Carbon (graphite) 32.808 --- --- ---
Hydrogen 120.971 --- --- ---
Carbon monoxide 10.112 --- --- ---
Ammonia 18.646 --- --- ---
Sulfur (solid) 9.163 --- --- ---

Note that there is no difference between the lower and higher heating values for the combustion of carbon, carbon monoxide and sulfur since no water is formed in combusting those substances.

References

  • "Carburants et moteurs", J-C Guibet, Publication de l'Institut Français du Pétrole, ISBN 2-7108-0704-1

See also

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Heat_of_combustion". A list of authors is available in Wikipedia.
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