01-03-08 Biodiesel is a non-petroleum based diesel fuel consisting of short chain fatty acid alkyl esters (methyl or ethyl esters), with colour ranging from golden to dark brown, depending on the production feedstock.
It is a cleaner burning diesel-replacement fuel made from natural, renewable sources such as new and used vegetable oils and animal fats. Just like petroleum diesel, biodiesel operates in compression-ignition engines.

Biodiesel can be used in pure form (B100) or may be blended with petroleum diesel at any concentration in most modern diesel engines. Blends of up to 20 % biodiesel (mixed with petroleum diesel fuels) can be used in nearly all diesel equipment and are compatible with most storage and distribution equipment.
These low-level blends (20 % and less) generally do not require any engine modifications, however, one should consult their OEM and engine warranty statement.

Biodiesel has physical properties very similar to conventional diesel. Some of the inherent physical characteristics of biodiesel are as follows:
-- Specific gravity: 0.87-0.89
-- Kinematic viscosity: 3.7-5.8 (at 40 degrees Celsius)
-- Cetane number: 46-70
-- Higher heating value: 16,928-17,996 Btu/lb
-- Sulphur: 0.0-0.0024 wt %
-- Cloud point: -11 to 16 degrees Celsius
-- Pour point: -15 to 13 degrees Celsius
-- Iodine number: 60-135
-- Lower heating value: 15,700-16,735 Btu/lb

Biodiesel has better lubricity than modern day diesels. In addition, it also reduces the wear and tear, thereby increasing the life of the fuel injection equipment that relies on the fuel for its lubrication, such as fuel injectors, high pressure injection pumps and pump injectors. Biodiesel can also provide the same payload capacity as diesel. Higher blends, (even 100 % biodiesel, or B100), may be able to be used in some engines (built since 1994) with little or no modification.
However, engine manufacturers are concerned about the impact of B100 on engine durability. Additionally, B100 is generally not suitable for use in low temperature conditions. Transportation and storage of B100, however, require special management.

Using biodiesel in a conventional diesel engine substantially reduces emissions of unburned hydrocarbons, carbon monoxide, sulphates, polycyclic aromatic hydrocarbons, nitrated polycyclic aromatic hydrocarbons, and particulate matter. These reductions increase as the amount of biodiesel blended into diesel fuel increases. The best emission reductions are seen with B100.
The use of biodiesel decreases the solid carbon fraction of particulate matter (since the oxygen in biodiesel enables more complete combustion to CO2) and reduces the sulphate fraction (biodiesel contains less than 15 ppm sulphur), while the soluble, or hydrocarbon, fraction stays the same or increases. Therefore, biodiesel works well with emission control technologies such as diesel oxidation catalysts (which reduce the soluble fraction of diesel particulate but not the solid carbon fraction).

However, there are many cons associated with the usage of biodiesels in vehicles; mostly those manufactured before 1992. Since biodiesel has different solvent properties than petro-diesel, there is high chance of it degrading natural rubber gaskets and hoses in vehicles. Also, biodiesel is known to break down deposits of residue in the fuel lines where petro-diesel has been used. The end result would be the clogging of fuel filter with particulates, if a quick transition to pure biodiesel is made. Hence, it is recommended to change the fuel filters on engines and heaters shortly after first switching to a biodiesel blend.
Emissions of nitrogen oxides increase with the concentration of biodiesel in the fuel and the increase is roughly 2 % for B20. Some types of biodiesel produce more nitrogen oxides than others, and some additives have shown promise in reducing the increases. Hence more R&D is needed to resolve this issue.

Biodiesel produced in Asia, South America and Africa are currently less expensive than those produced in Europe and North America suggesting that imports to these wealthier nations are likely to increase in future. Hence it can be a good future prospect for exports from countries like India, which has got rich biological reserves. Like all petroleum based fuels, biodiesel also requires a significant investment of energy before it arrives at petrol pumps, thus fair comparisons among fuels require full lifecycle analyses for each fuel type.
Lots of research is going on in finding more suitable crops and improving oil yield. Using the current yields, vast amounts of land and fresh water would be needed to produce enough oil to completely replace the conventional petroleum-based fuels.

Researchers have also been able to identify certain algae that have a natural oil content greater than 50 %, which could even be grown on ponds or waste water treatment plants. These oil-rich algae can then be extracted from the system and processed into biodiesel. However, the production of such oil-rich algae for producing biodiesel, has not yet been undertaken on a commercial level; these are still at various stages of research, before becoming fully suitable for final production.
With the shortage of non-renewable forms of energy, there is only one way ahead -- to search for alternatives. Biodiesel is one such alternative, and a very good prospect, for fuelling the world of tomorrow.