Biofuels include oil extracts from a wide variety of sources including neem (Azadirachtaindica), mahua (Madhucaindica), mustard (Brassica campestris), castor (Ricinuscommunts) and karanj (Pongamiapinnata) as a blending substance for conventional fossil fuels like diesel.

The most commonly used biofuels include plant oils such as soya bean, sunflower and rapeseed that are blended with diesel. On the other hand, fermented sugar beets and cereals are used for making bioethanol, which is mixed in petrol. One of the most talked about biofuel option today is biodiesel—oil derived from vegetable sources and used as a substitute for diesel. Vegetable oil can be derived from both edible and non-edible oil sources. The non-edible oils commonly used for industrial purposes are produced from linseed, castor and oilseeds of trees like neem, mahua, kusum (Carthanusoxycanthus), karanj, sal (Shorearobusta), mango (Mangiferaindica) kernels, (Garciniaindica) and dhupa (Simarubaglauca).

Problems 

• These oils are too viscous. Therefore, for least engine modifications and its efficient performance, vegetable oils are converted into their methyl esters so that the viscosity decreases. For doing so, vegetable oils are reacted with methyl alcohol in the presence of a catalyst.
• Along with having lower viscosity, biodiesel has a high cetane number of 58, which is an indicator of fuel ignition efficiency.

Advantages

• It has no sulphur or aromatics.
• The biofuel fraction in diesel is biodegradable, non-toxic and has high oxygen content for efficient combustion.