The type of energy produced when a fuel is burned is known as thermal energy or heat energy. This energy results from the combustion process, during which chemical bonds in the fuel break and form new bonds with oxygen, releasing energy. This transformation is often harnessed for practical uses, such as powering engines or generating electricity. The combustion of fossil fuels, however, contributes to environmental issues like air pollution and greenhouse gas emissions, prompting a shift towards cleaner energy sources.