Diesel engines play a vital role in modern life , but it causes problems like pollution. One solution to avoid the ewin problem of environmental pollution and energy shortage will be a carefully planned gradual shift of our economy from fossil fuels to renewable sources of energy. These renewable sources of energy is mainly contributed by fuels of bio-origin.
The fuels of bio-origin may be alcohol,editable and non editable vegetable oils, biomass, biogas etc. Some of these fuels can be used directly while the others need to be formulated to bring the relevant properties close to conventional fuels. Methanol and ethanol are two accepted alternative fuels, which posses the potential to be produced from bio mass resources. But they are not well suited to be used in diesel engines. In the case of alcohol it produces aldehydes and ketones in their exhaust, which creates associated environmental and health problems.
The main alternative fuel in the present is bio-diesel. It is the name of clean burning monoalkyl esters basedoxygenated fue, produced form vegetable oil. These fules contain no petroleum but can be blended at any level with petroleum diesel to create bio diesel blend. It can be used in the compression ignition engine without any major modification. It is simple to use, biodegradable, non toxic and essentially free of sulphur and aromatic compounds. Biodiesel is renewable and can be produced from agricultural and farm resources.The molecular structure of vegetable oil is similar to that of diesel, but it contains additional oxygen which reduces soot.
Though it has lot of advantages the use of vegetable oil as fuel face many problems.
Viscosity of vegetable oil is very high, which influences the shape of fuel spray. High viscosity causes poor atomization, large droplets and high spray jet penetration. With high viscosities the jet tends to be a solid stream instead of a spray of droplets. As a result proper mixing of fuel doesn?t occur. This results in poor combustion resulting in loss of power and economy.
The problems with use of biodiesel can be divided as :
1) Engine modifications.
- Duel fuelling
- Injection system modification
- Heated fuel lines.
2) Fuel modifications.
- Hydrogenation to reduce polymerization
The advantages of biodiesel are
Decrease in the smoke density and NOx to a level lower than the baseline diesel engine.
Improvement in brake thermal efficiency.
Flash and fire points are comparatively higher for esters, thus reducing fire hazards.
Higher injection pressure.
Engine shows better performance for blends with diesel rather than pure ester.
Cost of bio diesel production is comparatively more than diesel but it can be reduced by mass production.
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