For both kind of fuel and operating conditions, PM and SOF showed high emission rate at lower engine loads and decreased with an increase in engine load to be minimized at 75% engine load. These results agreed with that the fuel injection timing of the experimental engine was fixed to minimize the fuel consumption rate nearby 75% engine load similar to common marino Diesel engines. Moreover, using of MFO raised SOF emission rate as well as total PM compared with MDO, which suggests MFO would not only provide more sulphate emission but also affect SOF formation and increase it. In addition, SOF/PM ratio decreased with an increase in engine load for MDO while its change was not so obvious for MFO. The ratio showed higher value for propeller performance than for generator performance, and similarly showed higher for MDO than for MFO. These results suggest that unburnt carbon in PM decreased relatively with an increase in engine load while other components increased.
Then, detailed chemical aspects were investigated in focus on PM from MDO for propeller performance. After Soxhlet extraction, sulphate ion was separated and analyzed by IC to measure sulphate in ISF. The mass of soot was obtained by subtracting the mass of SOF, sulphate ion and binding water from the mass of PM. The detailed PM composition obtained by the above analysis is shown in Fig.4. The ratios of soot, sulphate and binding water in PM were raised with an increase in engine load while SOF/PM ratio was lowered, that is, an increase in engine load improved combustion so that SOF as unburnt carbon doereased although soot and sulphate as combustion products increased.
