heat of combustion

The Heat of combustion (Δ_cH⁰) 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 units;

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 (Δ_fH⁰) of the products and reactants.

Heating value

The heat of combustion for fuels is sometimes expressed as the HHV (Higher Heating value), LHV (Lower Heating Value), or GHV (Gross Heating Value). Lower heating value accounts for water in the exhaust leaving as vapor. The energy required to vaporize the water therefore is not realized as heat. Gross heating value accounts for water in the exhaust leaving as vapor, and includes liquid water in the fuel prior to combustion. This value is important for fuels like wood or coal, which will usually contain some amount of water prior to burning. Higher Heating Value is the same as the 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

colspan="4" \| Heat of Combustion
Fuel	MJ/kg	BTU/lb	kJ/mol
Hydrogen	141.6	61,000	286
Gasoline	47.3	20,400	---
Diesel	44.8	19,300	---
Ethanol	29.7	12,800	1,300
Butane	48.6	20,900	2,800
Wood	15	6,500	---
Coal	15-27	8,000 - 14,000	---

Heat Of Combustion

Heating value

Heat of combustion for common fuels

See also