ABSTRACT
Fossil fuels (oil, natural gas, and coal) presently represent about 90% of the world’s total commercial primary energy. But they are depletable sources of energy. Growth in the production of easily accessible oil, the main source of high-energy liquid transportation fuels, will not match the projected rate of growth demand, especially in developing countries. In the transport sector today, the only alternative to nonsustainable fossil fuels are biofuels, which are produced from biomass, a stored environmentally neutral solar energy. These fuels are compatible with current vehicles and are blendable with conventional fuels. Moreover, they share the long-established distribution infrastructure with little, if any, modification on existing equipment. The main biofuels presently in commercial production are bioethanol and biodiesel. Industrialized countries started production of the first-generation bioethanol and biodiesel from food products (grains and edible oils) a few decades ago, and these fuels are currently available at petrol stations. Biodiesel is methyl or ethyl esters of different fatty acids obtained from vegetable oils (triglycerides). Methods to obtain biodiesel are explained including conditions and catalysts used. A comparison between petroleum diesel and biodiesel is performed, and suggested ways to reduce the difference in efficiency and other parameters between the two are reviewed. Tribological advantageous and disadvantageous issues of biodiesel and petroleum diesel–biodiesel were also reviewed.
