Solid fuel liquid gas:A fuel is a substance that produces useful energy as a result of (usually chemical) changes that can later be converted into mechanical energy. These changes are usually accompanied by burning (i.e. combining with oxygen). The processes used to convert fuel into energy include: various chemical reactions and exothermic nuclear reactions such as nuclear fission or nuclear fusion. Hydrocarbons are by far the most common source of fuel used by humans, but in many cases radioactive metals are also used.
Chemical fuel and its types

Chemical fuels are materials that release energy through the reaction with the materials around them, the most important of which is through the oxidation process.

Types of fuel

There are different types of fuels. They can generally be divided into three groups: solid, liquid and gas.
solid fuel

They include materials such as wood, coal and coke. Humans have used wood as fuel for thousands of years. This material is the first fuel that has been used. Paraffin and tallow are two other types of solid fuel. These materials are usually used to make candles. Among solid fuels, coal is still the most consumed and abundant fuel in the world. The main use of this material is in the production of electricity.

liquid fuel

Most liquid fuels are derived from crude oil. Gasoline, kerosene and diesel are all derived from crude oil. In some countries, alcohol is used as fuel. Vegetable and animal oils are also a type of liquid fuel.

Gas fuel

Natural gas, coal gas and water gas are the most important types of gaseous fuels. Natural gas is mostly used in cooking and heat production. This gas can be found deep in the earth and in the vicinity of oil fields. Coal gas is a mixture of hydrogen, methane and other hydrocarbons, carbon monoxide and a little nitrogen, oxygen and carbon dioxide. This gas is produced when coal is converted into coke. Coal gas is used to generate electricity in metal smelting plants. Water gas is a combination of hydrogen and carbon monoxide gases. This gas is obtained by passing water vapor over hot coke and it is used in various industries. Butane gas is another important gaseous fuel.