3-2. Cylinder oil feed rate and cooling water temperature
Figure 3 and 4 show the relation between the cylinder oil feed quantity and particulate concentration at 25% and 100% engine load, respectively. The axis of abscissa indicates the oil feed quantity for each revolution of the engine and the left and right axises of ordinates indicate the particulate concentration (grams of particulate per cubic meter of exhaust gas in normal-state) and the ratio of SOF to the particulate, respectively. In this experiment, cylinder oil feed quantity of 0.14 cc/rev. correspond to oil feed rate of 1.28 g/kWh at 100% load. Both concentration of particulate and SOF increase with an increase in oil feed quantity, and this tendency becomes even stronger at lower engine load. The ratio of SOF weight to the total particulate weight is shown by a polygonal line and increases slightly with an increase in oil feed quantity.
The relations between temperature of the cylinder jacket cooling water and the particulate concentration at 25% and 100% load are shown in Figs. 5 and 6, respectively. From these figures, it is found that the SOF emission slightly increases and ISF emission decreases with an increase in the temperature of cylinder cooling water. As a result, the total particulate emission did not change with the cooling water temperature. The experimental result for high speed four-stroke diesel engine[5] shows that the SOF emission decreases with the temperature of cooling water since the SOF formation in the vicinity of the cylindcr wall is suppressed due to the high cylinder wall temperature. As a reason why SOF emission increases with cooling water temperature for two-stroke engine, SOF formation from the cylinder oil mist is promoted due to the high temperature of the cylinder wall as mentioned above.
The SOF obtained in the experiment was analyzed by gas chromatography, and Fig.7 shows the gas chromatogram of SOF at 85% load as a example of the results. The gas chromatogram of the fuel and cylinder oil are also shown in Figs. 8 and 9, respectively. In Fig.7, the first peek which appears in a retention time from 16 min. to 28 min. corresponds to paraffin components with boiling point higher than 570 K in the fuel, so that large part of SOF is thought to be derived from the fuel oil.
Fig.3 Effect of cylinder lubricating oil feed rate on particulate emission. (Engine load: 25%)
Fig.4 Effect of cylinder lubricating oil feed rate on particulate emission. (Engine load: 100%)
Fig.5 Effect of cylinder cooling water temperature on particulate emission. (Engine load: 25%)
Fig.6 Effect of cylinder cooling water temperature on particulate emission. (Engine load: 100%)
