Fuels are substances, which, when burned or consumed, produce energy. Fuels in use today are mostly derived from petroleum. Fuels, which are not derived from petroleum, are known as alternative fuels, since they provide an alternative source of energy. Alternative fuels include natural gas, propane, hydrogen, biofuels, alcohol and other fuels. This book will serve as a complete reference for students of several disciplines like thermal engineering, automotive engineering, mechanical engineering, chemical engineering and energy studies & engineering, where alternative fuels is offered as an elective. It will also serve as a valuable reference for practicing engineers and scientists, working in similar field.