Abstract
Keywords - Diesel Engines, Alternative Fuel, Biodiesel, Palm Oil, Exhaust Emissions
Abstract - From an ecological point of view, many researches on biodiesel produced from vegetable oils have been carried out because vegetable oils are a renewable, biodegradable and nontoxic fuel with the potential of carbon dioxide suppression. Palm oil will be one of effective vegetable oils as alternative diesel fuel because of the high productivity and low cost. The fatty acid composition of palm oil is different from rapeseed and soybean oils, or palm oil contains larger amounts of saturated fatty acid such as palmitic acid. Therefore, if Palm Oil Methyl Ester (PME) is used for diesel engines, the engine performance and exhaust emissions for PME may be different from rapeseed oil methyl ester (RME) and soybean oil methyl ester.
In this study, to utilize PME as an alternative diesel fuel, the combustion characteristics and exhaust emissions for PME are investigated using a DI diesel engine. RME and gas oil also be tested to compare with PME. As a result, the ignition delay of PME is shorter than those of RME and gas oil. The brake thermal efficiency with PME is almost the same as those with RME and gas oil. NOx and Smoke emissions from PME are simultaneously lower than those from gas oil. According to the results, it is concluded that PME can be used as an alternative diesel fuel.
Moreover, biodiesel such as PME and RME is a mixture of the fatty acid methyl esters. Therefore, the diesel combustion of the blended fuels of the oleic and palmitic acid methyl esters are investigated to understand the effects of the fatty acid methyl ester composition on biodiesel combustion, and to clarify the better ignitionability of PME compared with RME. As a result, ignition delay and NOx emissions decrease with higher weight percent of palmitic acid methyl ester in the blended fuels. It is considered that the ignitionability of palmitic acid methyl ester is better than that of oleic acid methyl ester because of the lower boiling point of palmitic acid methyl ester. Therefore, it is considered that because PME contains larger amount of palmitic acid methyl ester with lower boiling point and smaller amount of linoleic and linolenic acid methyl esters with higher boiling point, PME has better ignitionability compared with RME.
However, because PME has the high pour point, 12.5 ºC, it is not appropriate property for the use of PME in the cold region. Therefore, the blended fuels of PME with gas oil also are tested to improve the pour point and to use PME in lower ambient temperature. As a result, the pour point of the blended fuel with 50 weight percent of gas oil reduces to 0 ºC. Exhaust emissions of the blended fuels are reduced with higher weight percent of PME.