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Considerable amounts (400 ∼ 600 thousand tons) of waste vegetable oil in Japan are still flushed down the drain every year. Utilization of waste vegetable oil for diesel fuel leads to two advantages for environmental protection, to reduce CO2 emission from engines and to avoid water pollution of rivers. In this study, combustion characteristics of waste vegetable oil methyl ester (WME) are investigated in detail by not only engine test run but also observation of burning flames in a visual engine. As results indicate, WME shows rather better combustion state in the visual engine and lower smoke emission from a high-speed DI test engine than gas oil. Moreover, by emulsifying WME with water, further improvement of combustion and more than 18 % reduction of NOx emission is carried out.

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.

With progression of so-called shale gas revolution, gas engines are expected as a strong substitute for diesel engines in marine fields, where strict emission regulations have been recently introduced. Thanks to the sulphur-free and low-carbon features of natural gas, gas engines emit much less CO2 and particulate matter than marine diesels burning heavy fuel oil. The premixed lean-burn gas engines, however, suffer two massive flaws. One is abnormal combustion called knocking and the other is a methane slip, which substantially means the unburned methane emitted into exhaust ports. One of the methane slip sources is thought to be flame quenching inside dead volumes around a combustion chamber or inside a boundary layer near a cylinder wall. Only supportive measures like cutdown of crevice volume have been conducted against the unburned methane.

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.