Heat Released by Fuel Combustion
Heat Released by Fuel Combustion
Every combustion calculation — sizing a boiler, checking a generator's fuel consumption, or estimating a fire's energy release — starts from the same basic bookkeeping: energy released equals fuel mass burned times the fuel's heating value, a property measured in a bomb calorimeter and tabulated for every common fuel. Because heating value varies by a factor of two or more between fuels (natural gas versus wood versus diesel), using the wrong value or confusing higher and lower heating value is a common source of error in combustion sizing calculations, so this worksheet keeps the bookkeeping explicit.
The heat released is E = m·HHV, the fuel mass times its higher heating value. where m is the mass of fuel burned and HHV is the higher heating value, the energy released per unit mass including latent heat recovered from condensing the combustion water vapor.
Inputs
m_fuel := 5 kg=5 kg
HHV_fuel := 44 MJ/kg=4.4e+07 m^2/s^2
Multiplying the fuel mass by its heating value converts a quantity of fuel into the total chemical energy it can release on complete combustion.
E_comb := m_fuel·HHV_fuel=2.2e+08 Nm
Results
With diesel-like fuel at 44 MJ/kg, 5 kg releases about 220 MJ, enough to be a meaningful design number for a generator or space heater sized in kilowatts over an operating period. In practice only part of this energy ends up as useful output — combustion efficiency, flue gas losses, and incomplete combustion all shave off some fraction — so E_comb is the theoretical ceiling, not the delivered energy. If a lower heating value fuel were used instead, the same mass would release noticeably less usable energy since HHV includes latent heat that is often not recovered.
Assumptions & limitations
- Complete combustion assumed (no unburned fuel or soot).
- HHV corresponds to product water fully condensed, which most real equipment does not recover.
- No credit or penalty taken for combustion air preheat or excess air.
- Fuel composition assumed uniform and matches the tabulated HHV.