Lipids as a Source of Biodiesel, Engine Combustion, Limiting Factor, Biodiesel Production, Biomass, Mineral Nutrient Limitation

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	Lipids as a Source of Biodiesel- Lipids are accumulated in seeds of many plant species like sunflower, rapeseed, linseed, soybean, safflower, peanut, olive, etc. and by some algae. The lipids have high energy value and can be burnt to heat boilers or used as diesel engine fuel. However, the oils are not easily injectable into the engine combustion chamber due to their high viscosity. This problem is overcome by producing esters of the lipid fatty acids. The esterified lipid fatty acids constitute 'biodiesel' and can be used in unblended form in normal diesel engine with little or no modification in the engine. Use of such a biodiesel is expected to produce much lower emissions than diesel, but the cost of production of biodiesel is the limiting factor.
Even so, there is a growing interest in oilseed based biodiesel production in some European countries and U.S.A. In developing countries, on the other hand, vegetable oils command a much higher price than diesel; this is particularly true for edible oils. In addition, there is generally a shortage of lipids. Thus it is highly unlikely that vegetable lipid derived biodiesel would be used on any scale in the developing countries. Some algae may accumulate up to 60% of their biomass as lipids, especially when they are grown under conditions of mineral nutrient limitation. The reduced electron carriers used for the production of new cells under conditions of nutrient sufficiency are diverted to produce lipids under nutrition deficient conditions. Efforts are being made to develop these algae as valuable sources of lipids to be used for producing biodiesel.