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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.

Dual fuel diesel engines using compressed natural gas (CNG) are an attractive low polluting application, because natural gas is a clean low CO2 emitting fuel with superior resource availability. In dual fuel diesel engines with CNG as the main fuel the natural gas is supplied from the intake-pipe and the pre-mixture formed in the cylinder is spontaneously ignited by an injected spray of ordinary diesel fuel. Dual fuel engines of this type have the advantages that only limited engine modifications are needed and that low calorie gas fuels such as biogas can be used. To reduce NOx emissions in the dual fuel operation, the present study conducted the diesel combustion with a setup similar to that used with EGR. To dilute the intake air, the experiments used N2 or CO2 gases which are the major components of EGR. The diluent gas addition ratio was defined as the mass ratio of the supplied diluent to the intake charge which is composed of air and diluent.

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.

The diesel combustion characteristics and the exhaust emissions of biodiesel are affected by the composition of fatty acid methyl esters (FAMEs). In this study, the combustion characteristics and the exhaust emissions from single compositions of FAMEs, such as methyl palmitate, methyl oleate and the others, are investigated by using a single cylinder DI diesel engine. Experimental five FAME fuels are neat methyl oleate and the rest are blended mixtures based on methyl oleate. From the experimental results, the ignition delays of saturated FAMEs decrease with longer straight chain of the hydrocarbon molecules while in the same carbon number FAMEs, the ignition delays increase by increasing carbon-carbon double bonds. The break thermal efficiencies of the five FAME fuels and the gas oil are almost the same.

In order to reduce NOx and smoke emissions of palm oil methyl ester (PME), the combustion characteristics and exhaust emissions for emulsified PME were investigated using a single cylinder DI diesel engine. As the results, stable emulsified PME can be obtained without adding any emulsifier like as emulsified rapeseed oil methyl ester (RME). Emulsified PME is able to reduce NOx and smoke emissions as emulsified RME. The optimum water mass fraction for emulsified PME is 15wt% with regard to the exhaust emissions. The ignition delay of emulsified PME with 15wt% water is almost the same as that of gas oil because of the higher ignitionability of PME. Due to the higher ignitionability and better combustion characteristics of PME, emulsified PME with 15wt% water has shorter ignition delay and lower NOx, HC, CO and smoke emissions compared with emulsified RME with 15wt% water.