- b : nutritive material
- c : a material from which atomic energy can be liberated especially in a reactor
- 2: a source of sustenance or incentive : reinforcement
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air. Other processes used to convert fuel into energy include various other exothermic chemical reactions and nuclear reactions, such as nuclear fission or nuclear fusion. Fuels are also used in the cells of organisms in a process known as cellular respiration, where organic molecules are oxidized to release usable energy. Hydrocarbons are by far the most common source of fuel used by humans, but other substances, including radioactive metals, are also utilized.
The first use of fuel was the combustion of wood or sticks by Homo erectus near 2 million years ago. Throughout the majority of human history, fuels derived from plants or animal fat were the only ones available for human use. Charcoal, a wood derivative, has been used since at least 6,000 BCE for melting metals. It was only supplanted by coke, derived from coal, as the forests started to become depleted around the 18th century. Charcoal briquettes are now commonly used as a fuel for barbecue cooking.
Coal was first used as a fuel around 1000 BCE in China. With the development of the steam engine in 1769, coal came into more common use as a power source. Coal was later used to drive ships and locomotives. By the 19th century, gas extracted from coal was being used for street lighting in London. In the 20th century, the primary use of coal is for the generation of electricity, providing 40% of the world's electrical power supply in 2005.
Fossil fuels were rapidly adopted during the industrial revolution, because they were more flexible than traditional energy sources, such as water power.