It is fair to say that a very substantial part (more than 90 percent) of the total energy used today in transportation, power production, space heating and domestic cooking is produced by combustion (burning) of solid, liquid and gaseous fuels. Although the phenomenon of combustion was known to the earliest man, and although great strides have been made through painstaking experimental and theoretical research to understand this phenomenon and to use this understanding in designs of practical equipment (principally, burners and combustion chambers or furnaces), any claim to a perfect science of combustion remains as elusive as ever. Designers of combustion equipment thus rely greatly on experimental data and empirical correlations.

Combustion is a phenomenon that involves the change in the chemical state of a substance from a fuel state to a product state via a chemical reaction accompanied by release of heat energy. To the extent that a change of state is involved, the laws of thermodynamics provide the backbone to the study of combustion. Design of practical combustion equipment, however, requires further information in the form of the rate of change of state. This information is provided by the empirical sciences of heat and mass transfer, coupled with chemical kinetics. The rate of change is also governed by fluid mechanics.

The heat released by combustion is principally used to produce mechanical work in engines and power plants, or is used directly in applications such as space-heating or cooking.