What is fuel proper definition?

Answer 1

Fuels are any materials that store potential energy in forms that can be practicably released and used for work or as heat energy. The concept originally applied solely to those materials storing energy in the form of chemical energy that could be released through combustion,[1] but the concept has since been also applied to other sources of heat energy such as nuclear energy (via nuclear fission or fusion energy). Generally speaking, fuel is:

• Something consumed to produce energy, especially:

• A material such as wood, coal, gas, or oil burned to produce heat or power.

• Fissionable material used in a nuclear reactor.

• Nutritive material metabolized by a living organism; food.

• Something that maintains or stimulates an activity or emotion:" Money is the fuel of a volunteer organization" (Natalie de Combray).