fuel

Fuel is any material that stores energy and can be converted into useful heat, light, motion, or electricity. Fuels release energy through chemical reactions or other processes when used in engines, turbines, or reactors. The usefulness of a fuel is measured by its energy content and how efficiently that energy can be converted in a given application.

Fuels are commonly classified by state: solid fuels (coal, charcoal, wood), liquids (gasoline, diesel, ethanol, biodiesel), and gases (natural gas, hydrogen). They can be described as primary fuels found in nature, or secondary fuels produced from primary fuels, such as gasoline derived from crude oil. Nuclear fuels, such as uranium, release energy in reactors through fission and are used for large-scale electricity generation, with high energy density and different handling requirements.

Environmental and economic considerations shape fuel choices. Combustion of fossil fuels emits carbon dioxide and other pollutants, contributing to climate change and air quality concerns. Life cycle factors—extraction, processing, transport, and use—affect total impact. Energy density, storage, and infrastructure influence suitability: liquids and gases are common in transportation and heating, while electricity and hydrogen offer low-emission end uses but require accompanying production and storage solutions.

Applications and infrastructure vary by fuel type. Fuels power transportation (cars, trucks, airplanes), provide heat for buildings, and drive electricity generation in power plants. Storage and safety are important considerations, with pipelines, tanks, and storage terminals supporting distribution. Global energy systems continue to evolve toward greater efficiency and lower emissions, balancing availability, cost, and environmental impact.