On the other hand, in a longer retention time than 28 min., another peek appears and its coincides with the pattern of the gas chromatogram of the cylinder oil.
3-3. Cetane index of the fuel
Figures 10, 11 and 12 show the relation between the engine load and particulate emission at propeller load operation with MDO-1, mixed fuel and MDO-2, respectively. In these figures, the particulate concentration increases with the engine load. The relation between particulate concentration and cetane index of the fuel is shown in Fig.13. The particulate concentration increases with an increase in cetane index when the engine is operated at 85% or 100% load. On the other hand, results for low loads show that particulate concentration is nearly independent of cetane index. Since the test engine is low speed, the experimental data show that the ignition delay period and the cylinder pressure curve are independent of the cetane index within the limits of this experiment. Therefore the fact that sulphur content and carbon residue of MDO-1 are higher than that of MDO-2 seems to be the reason of the variation of the SOF concentration obtained here.
Fig.13 Relation between cetane index of the fuel and particulate emission.
3-4. Influence of engine operation mode
The relation between the engine load and particulate emission at constant speed operation with MDO-2 is shown in Fig.14. Figure 15 shows the comparison of the particulate emission characteristics of propeller load and constant speed operations. Although the particulate emission in propeller load operation is larger than that in constant speed operation, there is only a slight difference between both operation modes. Figure 16 shows the relation between the engine load and the particulate emission of the four-stroke engine in constant speed operation. It is found that the SOF emission is very much higher in the operation of the constant engine speed while ISF emission is almost the same level in both operations on comparing Fig.16 to Fig.2.
Fig.14 Particulate emission at constant engine speed operation with MDO-2.
Fig.15 Particulate emission at propeller load operation and constant speed operation.
