Properties and constituents of MDO-1 and MDO-2 are shown in Table 3.
The concentration of exhaust particulates was measured with the engine load changed both in propeller load and generator load operations. In the propeller load operation, the engine output is varied proportionally to the third power of engine speed, and in the generator load operation, the torque was varied at a constant engine speed of 188 rpm.
The particulate concentration was measured by the partial flow dilution method using a small sized dilution tunnel(70 mm inner diameter, 1400 mm length). The exhaust stream was split and only a small part of the exhaust gas is introduced to the tunnel by heating tube. As the tunnel size is small in comparison to the engine size, the split ratio has a very small value (about 1:2000). Dilution ratio was determined by dividing the NOx concentration of raw exhaust gas by the diluted NOx concentration. For the particulate sampling, a portion of the diluted exhaust gas is passed to a filter holder, and particulate is collected on a fluorocarbon coated glass fiber filter which has a diameter of 47mm. The mass of collected particulate was determined from the difference of the filter weights before and after filtration of particulates. The filters were placed in the air-conditioned room (the temperature was maintained to 297 K within an error of 2 K and the relative humidity was maintained to 45% within an error of 5%) at least 8 hours prior to weighing. After weighed, the particulates collected on a filter was extracted for 16 hours in a Soxlet extractor by using dichrolomethane as a solvent. The extract part was weighed as SOF, and the difference between the SOF weight and the particulate weight was determined as ISF(insoluble organic fraction).
3. EXPERIMENTAL RESULTS
3-1. Influence of Engine load
Figure 1 shows the relation between the engine load and particulate emission in the propeller load operation. The emission of particulate, SOF and ISF increase with an increase in engine load. To compare the observation data, particulate measurement for a four-stroke trunk-piston type diesel engine (Direct injection diesel engine with exhaust turbo charger, Bore: 130 mm, Stroke: 160 mm, Output: 73.5 kW, Engine speed: 1200 rpm, Number of cylinder: 3) was conducted. The relation between the engine load and particulate emission from the four-stroke engine in the propeller load operation is shown in Fig.2. SOF emission becomes the highest at a 30% load, while it is nearly constant at the other load. ISF emission tends to increase with an increase in engine load. Because of low temperature of the cylinder wall and long ignition delay, SOF emission is thought to become the highest at 30% load.
In comparison of the results for two-stroke engine with four-stroke engine, there are differences in that the SOF emission increases with the engine load, and the ratio of SOF to the total particulate is large even at high engine loads. As reasons of these differences, the following are pointed out: firstly at low loads the SOF emission decreases because the flame dose not reach near the vicinity of the cylinder wall since the fuel injection quantity is small and the cylinder bore size is large for two-stroke engine, secondly at high loads cylinder oil mist tends to be exhaust as SOF due to the high temperature of the cylinder wall.