22-10-2012, 05:56 PM
BIO DIESEL: AN ALTERNATIVE FUEL FOR COMPERSSION IGNITION ENGINES
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ABSTRACT
Biodiesel is an alternative fuel for diesel engines that is produced by chemically combining vegetable oils and Animal fats with an alcohol to form alkyl esters. Extensive research and demonstration projects have shown it can be used Pure or in blends with conventional diesel fuel in unmodified diesel engines. Interest in biodiesel has been expanding recently Due to government incentives and high petroleum prices. This paper reviews the history of biodiesel development, Production practices, and the technology to utilize the fuel without problems. A technical consensus has developed that Quality is the most important criterion of successful biodiesel use and that fuel should meet the ASTM specification for Biodiesel, D6751. When the fuel meets this standard, it has been shown to provide improved lubricity, higher cetane number, lower emissions of particulate, carbon monoxide, unburned hydrocarbons but higher level of oxides of nitrogen. While the current availability of vegetable oil limits the extent to which biodiesel can displace petroleum to a few percent, new oil crops could allow biodiesel to make a major contribution in the future.
INTRODUCTION
The esters of vegetable oils and animal fats are known Collectively as biodiesel, a renewable alternative fuel that has been shown to be direct replacement for diesel fuel in compression ignition engines. Biodiesel has an energy content that is about 12% less than petroleum-based diesel fuel on a mass basis. It has a higher molecular weight, viscosity, density, and flash point than diesel fuel. When biodiesel is compared to conventional diesel fuel in engine tests, the power and fuel consumption are in nearly direct proportion to the fuel’s energy contents. Biodiesel is an oxygen at fuel, 10% to 11% oxygen by weight, and produces less unburned hydrocarbons (HC), carbon monoxide (CO), and particulate matter (PM) than diesel-fueled engines. Carbondioxide (CO2) is recycled through the process of photosynthesis in growing the oilseeds making biodiesel nearly CO2neutral. Oxides of nitrogen (NOx) are increased by 10% to 15% when fueling with 100% biodiesel. Biodiesel fuels are good for the environment because they are also readily biodegradable ,a benefit in case of spills.
FUNDAMENTALS OF BIODIESEL CHEMISTRY
Biodiesel is produced through a process known as transesterification . This is a chemical process whereby an ester is reacted with an alcohol to form another ester and anotheralcohol. In the case of biodiesel, the reaction is shown below,where R1, R2, and R3 are long hydrocarbon chains,
sometimes called fatty acid chains
ENGINE COMPATIBILITY
Biodiesel can be produced in quantities that can supplement but not replace petroleum diesel .Therefore most CI engines will continue to be designed to use petroleum diesels their primary fuel. An important advantage of biodiesel that it can function in these engines without modifications ,and does not require engines especially designed to run on biodiesel. When B100 is used as a fuel for CI engines, the following issues arise: solvent action, storability, cold filter plugging, elastomer compatibility, cetane number, heating
value, and lubricating oil dilution.
Solvent action—Biodiesel has excellent solvent action. When spilled on paint, it can cause paint deterioration unless the spilled fuel is removed immediately. Biodiesel can also loosen deposits that have accumulated in the fuel tank and cause filter plugging until the tank, fuel lines, and filters are cleared of the deposits.
Storability—Because of its high level of unsaturation, biodiesel is susceptible to attack by oxygen from the air
producing peroxides, acids, aldehydes , and viscosity increasing polymers. Anti-oxidant additives should be used to control this process if the fuel must be stored longer than six months before use. Two additional issues arise with extended storage of biodiesel in the fuel tank. The fuel can bond with water, creating acids. Biodiesel is also a good medium for microbial growth and such growth is accelerated by the presence of water. Both problems can be addressed by measures to keep water out of the fuel tank, for example, by keeping the tank full during idle periods to preven thumid air from condensing water on the tank inner walls.