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:
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.
The heating value or calorific value of a substance, usually a fuel or food, is the amount of heat released during the combustion of a specified amount of it. The calorific value is a characteristic for each substance. It is measured in units of energy per unit of the substance, usually mass, such as: kcal/kg, kJ/kg, J/mol, Btu/m³. Heating value is commonly determined by use of a bomb calorimeter.
The heat of combustion for fuels is expressed as the HHV, LHV, or GHV:
Most applications which burn fuel produce water vapor which is not used, and thus wasting its heat content. In such applications, the lower heating value is the applicable measure. This is particularly relevant for natural gas, whose high hydrogen content produces much water. The gross calorific value is relevant for gas burnt in condensing boilers which condense the water vapor produced by combustion, recovering heat which would otherwise be wasted.
Both HHV and LHV can be expressed in terms of AR (all moisture counted), MF and MAF (only water from combustion of hydrogen). AR, MF, and MAF are commonly used for indicating the heating values of coal:
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 |
Fuel | MJ/kg | MJ/L | BTU/lb | kJ/mol |
---|---|---|---|---|
Paraffins | ||||
Methane | 50.009 | — | — | — |
Ethane | 47.794 | — | — | — |
Propane | 46.357 | — | — | — |
Butane | 45.752 | — | — | — |
Pentane | 45.357 | - | — | — |
Hexane | 44.752 | - | — | — |
Heptane | 44.566 | - | — | — |
Octane | 44.427 | - | — | — |
Nonane | 44.311 | - | — | — |
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 | - | — | — |
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 | - | — | — |
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.
Fuel | HHV MJ/kg | HHV BTU/lb | HHV kJ/mol | LHV MJ/kg |
---|---|---|---|---|
Hydrogen | 141.8 | 61,100 | 286 | 121 |
Methane | 55.5 | 23,900 | 889 | 50.0 |
Ethane | 51.9 | 22,400 | 1570 | 47.8 |
Propane | 50.35 | 21,700 | 2220 | 46.35 |
Butane | 49.5 | 20,900 | 2875 | 45.75 |
Pentane | 45.35 | |||
Gasoline | 47.3 | 20,400 | 44.4 | |
Paraffin | 46 | 19,900 | 16,300 | |
Kerosene | 46.2 | 43.0 | ||
Diesel | 44.8 | 19,300 | ||
Coal | 15–27 | 8000–14,000 | 200–350 | |
Wood | 15 | 6500 | 300 | |
Peat | 6–15 | 2500–6500 |
Fuel | HHV MJ/kg | BTU/lb | kJ/mol |
---|---|---|---|
Methanol | 22.7 | 9800 | 726 |
Ethanol | 29.7 | 12,800 | 1300 |
Propanol | 33.6 | 14,500 | 2020 |
Acetylene | 49.9 | 21,500 | 1300 |
Benzene | 41.8 | 18,000 | 3270 |
Ammonia | 22.5 | 9690 | 382 |
Hydrazine | 19.4 | 8370 | 622 |
Hexamine | 30.0 | 12,900 | 4200 |
Carbon | 32.8 | 14,100 | 393.5 |
These data on higher heating values were obtained from the International Energy Agency:
The lower heating values of the above natural gases are about 90 percent of the higher heating values.
(The fuel quantities below assume 100% conversion efficiency. As most power generation/distribution systems only achieve 30% - 35% efficiency, the actual quantity of fuel used to power a 100 W light bulb in your home will be about three times the quantity shown.)