2. PM MEASUREMENT AT SEA
2.1 Experimental Equipment and Method
A photo of the experimental ship "Koyo-Maru" is shown in Fig.1 and the principal specifications of experimental ship are indicated in Table 1. Fig.2 shows the measuring system of the exhaust emissions using the partial-flow dilution tunnel. As shown in this figure, the sampling probe made of stainless steel was inserted close to the silencer to sample the exhaust gas. After sampling, the exhaust gas was diluted with clean air for cooling. PM in the diluted exhaust gas was filtered with a primary and a back-up filter, which had been aged over 12 hours at the constant temperature (25℃) and the humidity (50%) before setting according to ISO/EPA regulations [5, 6]. After filtering, the filters were aged again at the same conditions as mentioned above. The filter loading is defined as the difference of the filter mass between before and after filtering. Dilution ratio can be known as the ratio of NOx (ppm) data of the exhaust gas between before and after diluting. To measure the SOF% in the PM emission, Soxhlet extractor was used.
At measurement, the engine speed was set at 170, 205, 215 rpm, and the engine load was changed by changing the CPP blade angle at each engine speed.
2.2 Experimental Result
Fig.3 shows the change in the PM emission expressed as g/kWh with engine load. The engine load is defined as the ratio of output horsepower to full load. The broken lines in the figure show the change in the PM emission along the generator characteristics at each engine speed. The solid line shows that along the propeller characteristics keeping the CPP blade angle at maximum. In this figure, the PM emission increases as the engine load is increased along both the generator and the propeller characteristics.
Comparing the three broken lines at the same engine load, the PM emission becomes more as the engine speed becomes lower. This is because Pmi (indicated mean effective pressure) becomes larger as the engine speed is reduced keeping the engine horsepower constant, which means the fuel quantity injected per one cycle becomes larger. Fig.4 shows the change in the PM emission per one cycle of one cylinder as function of Pmi. It is clear that the mass of PM emitted per one time combustion depends on Pmi independently of the engine speed.
Fig.5 shows the mass percent of SOF in the PM emission. According to this data, SOF% in the PM emission is limited in the range of 60〜70% at all three operating conditions. This result is a little different from the former study using a 4-cycle diesel engine [7], in which it was concluded that the PM emission was mainly consist of the dry soot.
As this engine is a 2-cycle engine, the cylinder lubricating oil is fed into the cylinder directly. An origin of the high amount of SOF in the PM emission is considered as this cylinder oil. In detail, as the distillation temperature of the cylinder oil is in the range of 250〜600℃, when the temperature of the oil film on the cylinder becomes higher than 250℃, some part of it will evaporate. This part will become liquid phase again after being cooled in the dilution tunnel. It could be an origin of SOF in the PM emission.
3. EXAMINATION OF MEASURING PROCEDURE
3.1 Experimental Equipment and Method
Examination of the measuring procedure was carried out using not the ship but the high-speed test engine on the bench. The principal specifications of the test engine are indicated in Table 2. The same partial-flow dilution tunnel as on the ship was applied. The sampling line of the exhaust gas is shown in Fig.6. The sampling probe was inserted to the outlet pipe of the turbo-charger.
