This paper describes two topics. One is a decrease in the fraction of methyl oleate ester in biodiesel fuel. study of the effects of biodiesel fuel physical properties on injection characteristics and spray behaviour. The study was done via numerical simulation of the injecKey words: biodiesel fuel, DI-CI engine, injection, combustion, emission tion system and via laser-sheet imaging of the spray. The second topic is a study of the effects of the constituents of biodiesel fuel on combustion and exhaust emis-

The objectives of this study are to clarify the influence of fuel physical properties on injection characteristics by means of numerical simulation of injection system fueled biodiesel fuel, and to clarify the influence of components of the fatty acid methyl ester on the engine performance and characteristics of exhaust emissions; PM, NOx, etc, including unregulated emissions by experiments. In these experiments, several kinds of biodiesel and methyl oleate and methyl linoleate were investigated, both of which are main chemical components in biodiesel (Table 1).The curves of bulk modulus depending on liquid pressure and temperature are different between gas oil and biodiesel. The computed simulations show that a at lower fuel temperature; 293 and 313 K, the injection pressure of biodiesel rises earlier than that of gas oil. This is because at lower liquid pressure, the bulk modulus of biodiesel is higher

The objective of this study was to experimentally clarify the effect of two-stage split and early injection on the combustion and emission characteristics of a direct-injection (DI) diesel engine. Engine tests were carried out using a single-cylinder high-speed DI diesel engine and an injection system, combining an ordinary jerk pump and an electronically controlled high-pressure injection system, KD-3. In these experiments to compare the combustion and exhaust emission characteristics with two-stage split and early injection, a single-stage and early injection was tested. The FT-IR exhaust-gas analyzer simultaneously measured the exhaust emissions of 26 components. The results showed that HCHO, CH3CHO, and CH3COOH were emitted during the very early stage of both single injection and two-stage injection. These concentrations were higher than those from diesel combustion with ordinary fuel injection timings. These exhaust emissions are characteristic components of combustion by premixed compression ignition with extremely early injection. In particular, the HCHO concentration in exhaust was reduced with an increase in the maximum rate of heat release after cool flame due to pre-reaction of pre-mixture. At extremely early injection, the NOx concentration was extremely low; however, the indicated specific fuel consumption (ISFC) was higher than that of ordinary diesel combustion. In the case of two-stage injection, the degree of constant volume is increased, so that ISFC is improved. These results also demonstrated the possibility of reducing HCHO, NOx, and smoke emissions by means of two-stage split and early injection.

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