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In order to improve the cold flow properties of coconut oil biodiesel and to reduce the lifecycle CO2 emission by using bio-alcohol at biodiesel manufacturing, varying the types of alcohol used at transesterification was examined. The pour point of coconut oil ester decreases as the carbon number of alcohol increases. Among 5 ester fuels, the pour point of coconut oil isobutyl ester (CiBE) made from isobutanol is lowest, −12.5 °C, compared to that of coconut oil methyl ester (CME), highest, −5 °C. The pour point of coconut oil 1-butyl ester (CBE) is −10 °C, second lowest. Furthermore, CBE, CiBE, CME and JIS No.2 diesel fuel (gas oil) were tested using a DI diesel engine. CBE and CiBE have shorter ignition delay compared to the gas oil although slightly longer than CME. CBE and CiBE have the same thermal efficiency and NOx emissions compared to the gas oil. HC, CO and Smoke emissions of coconut oil ester fuels slightly increase when the ester molecule carbon number increases.

In order to utilize tung oil as an alternative diesel fuel, the combustion characteristics and exhaust emissions of tung oil methyl ester (TME) were investigated by using a single cylinder DI diesel engine. Also the comparisons were carried out on combustion characteristics and exhaust emissions of TME with rapeseed oil methyl ester (RME) and JIS No.2 diesel fuel (gas oil). From the experimental results, the stable engine operation was achieved by fuelling TME as those of RME and the gas oil. The thermal efficiency of TME is almost the same as that of the gas oil. TME has longer ignition delay compared to the other test fuels due to the lower ignition ability. The pour point of TME is -7.5°C and that is the same as that of RME. The exhaust emissions (HC, CO, NOx and smoke) of TME are higher than those of RME and the gas oil. From the experimental results, it is necessary to improve the fuel properties of TME for better diesel combustion.

In order to determine the usefulness of coconut and palm oil biodiesels as alternative diesel fuel, the fuel properties, the combustion characteristics and the exhaust emissions were investigated. Therefore, the methyl esters of coconut, palm and rapeseed oils (CME, PME and RME) and the ethyl ester of palm and rapeseed oils (PEE and REE) were processed and tested using a DI diesel engine. From the experimental results, the thermal efficiency of CME is almost the same as the other test fuels and CME has the lowest HC, CO, NOx and smoke emissions among the test fuels. Also PEE has the same ignitibility as PME and the exhaust emissions of PEE are almost the same as PME. From this investigation, we can say that CME and PEE are favorable alternative diesel fuels to substitute for petroleum based diesel fuel.