Energetics of Combustion Reactions Reference Page
Fueling the Fire: The Shocking Truth About Combustion Reactions!

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Intro to Fueling the Fire: The Shocking Truth About Combustion Reactions!

Combustion reactions are among the most important energy-producing processes in engineering and everyday life.
They power engines, generate electricity, heat buildings, and drive many industrial processes.

To analyze combustion systems, we apply the First Law of Thermodynamics together with tabulated thermodynamic data such as heats of formation and heats of combustion. This page introduces the basic terminology used to describe fuels, heating values, and combustion behavior.

Fueling the Fire: The Shocking Truth About Combustion Reactions!

This video introduces common types of fuels and explains the thermodynamic quantities used to characterize combustion, including heating values and combustion energetics.

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Examples and Definitions

Definitions

Fuel
A substance that reacts with oxygen in an exothermic reaction, releasing energy in the form of heat.
Solid Fuels
Fuels in the solid state, such as coal, coke (pyrolyzed coal), wood, or charcoal (pyrolyzed wood).
Liquid Fuels
Fuels in the liquid state such as kerosene, methanol, or gasoline.
Gaseous Fuels
Fuels in the gaseous state such as natural gas or acetylene.
Coal
A naturally occurring solid fuel formed from vegetable matter subjected to heat and pressure over geologic time. Major classifications include anthracite, bituminous, subbituminous, and lignite.
Enthalpy or Heat of Combustion
The enthalpy change associated with the complete combustion of a fixed amount of fuel. It may be expressed on a per-mass or per-mole basis.
Lower Heating Value (LHV)
The heating value obtained when water formed during combustion remains in the vapor phase. The heating value is the negative of the heat of combustion under this assumption.
Higher Heating Value (HHV)
The heating value obtained when water formed during combustion is assumed to condense to liquid water.

Because condensation releases additional heat, the HHV is larger than the LHV.

Adiabatic Flame Temperature
The maximum temperature reached by a fuel–air mixture if combustion occurs with no heat transfer to the surroundings.
Flash Point
The temperature at which the vapor above a liquid fuel forms a combustible mixture with air that will ignite if exposed to an ignition source.
Autoignition Temperature
The temperature at which a fuel–air mixture will spontaneously ignite without an external ignition source.
Flammability Limits
The range of fuel–air compositions that can support combustion.

Below the lower flammability limit (LFL) there is too little fuel to sustain combustion.
Above the upper flammability limit (UFL) there is too little oxygen to sustain combustion.