The difference between filter weights before and after the filtration was determined to be a particulate weight. 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 was filtered under reduced pressure through a membrane filter and concentrated up to 1.0 ml by a rotary evaporator. The concentrated extract was transferred to a weighing bottle to be dried by blowing nitrogen gas. The extract obtained by the above procedure was weighed as SOF, and the difference between the SOF weight and the particulate weight was determined as ISF. The weighed SOF was analyzed by a GC-FID (gas chromatograph with FID) to study the characteristics of the components.
3. Experimental Results and Discussion
3.1 Experiment for Marine Four-stroke Diesel Engine
Fig.1 shows the relation between the engine load and particulate concentration in the propeller load operation. The axis of abscissas indicates the engine load and the left and right axes of ordinates indicate the particulate weight contained in 1 m3 of the exhaust gas in normal state and the ratios of SOF to the particulates respectively. As shown in the bar charts, SOF concentration becomes the highest at a 30% load factor while it is nearly constant at the other loads.
ISF concentration tends to increase with an increase in load. As a result, the total concentration of both particulates becomes a minimum at a 50% load. The ratio of SOF weight to the total particulate weight is shown by a polygonal line and decreases with an increase in load. In low loads, SOF is thought to be produced because the flame is cooled at the vicinity of the cylinder wall surface since its temperature is low. Also, an ignition delay measured at the time becomes the longest at a 30% load. It is said that a lean mixture zone tends to be produced at a long ignition delay and SOF tends to be produced at the lean mixture zone.
