Fuel additives are substances added to fuels to enhance their performance and efficiency. They can improve combustion, reduce emissions, and prevent engine deposits. Common types of fuel additives include detergents, which clean the fuel system, and octane boosters, which increase a fuel's resistance to knocking. These additives are used in various fuels, including gasoline and diesel. By optimizing fuel quality, they help engines run smoother and can lead to better fuel economy. Many vehicle manufacturers recommend specific fuel additives to maintain engine health and performance over time.