Abstract
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 than that of gas oil (Fig. 2), so that the rate of liquid pressurerise goes up and the injection timing is advanced. And peak injection pressure at biodiesel is higher than that at gas oil in the case of lower mean injection pressure. But, it becomes be similar to that at gas oil under higher mean injection pressure. At higher fuel temperatures, there are no differences in injection timing and pressure between biodiesel and gas-oil. From experimental obtained on DI-CI engine, SOF in PM by biodiesel emitted more than that by gas oil on a low engine load (Fig. 3). From the results obtained on spray visualization by the laser-sheet technique, it was found that the spray penetration by biodiesel become shorter than that by gas oil, so that the mixing of air and fuel deteriorated, and a fuel-rich mixture is formed and emitted as SOF. A SOF concentration and ignition delay increase corresponded with a decrease of the fraction of methyl oleate ester in biodiesel fuel. This will be due to low ignitability of methyl linoleate ester.
