(3-2) Exhaust gas emission sampling

 Exhaust gas emission data (NOx and O2 concentration) were continuously and automatically recorded on recorder all through each voyage. The recorded data were retrieved from memory system of the recorder by analyzer manufacturer when the ship returns to Japan.

　

 Calibrations of the analyzer were automatically carried out with interval of one time every week for 2^nd and 3^rd voyages by using program function of the analyzer. For 1^St voyage, calibrations the analyzer were cancelled by following reason (refer to 6.3.2). And also purge of sensor part were automatically carried out everyday through the all voyages.

.1 Span gas leak

 After sea trial on Jan.30.2002, the pressure of span gas (NO) bottle decreased from 12.5MPa to 10.0MPa in several days. Span gas was leaking from the connection part between span gas bottle and the analyzer. Until the ship return to Japan, calibrations of the analyzer was canceled, because NOx value of l^st and 2^nd test ships from 40^th to 88^th days drifted less than 2%FS. (It was confirmed that sampling data on sea trial were proper, because on that test calibration was carried out manually and NOx value was proper.)

　

.2 Setting of NOx value indication

 After analysis of sampling data of 1^st voyage, it was cleared that the NOx value on 1^st voyage were 13% 02 conversion NOx value. For that reason, the sampling data of 1^st voyage were converted to net value and setting of NOx value indication was changed to net value.

.1 Long-term monitoring data

 Fig.6.3.3.1-Fig.6.3.3.10 respectively show the whole NOx and 02 monitoring data of each voyage. After sea trial, as the indications of NOx and 02 concentration periodically show 0 ppm and about 21%, they are the timing of air purge everyday. Same as the above, automatic calibration indications once a week are also recorded.

　

.2 1Hr data

 Fig. 6.3.3.11-Fig.6.3.3.13 show 1Hr interval sampling data, which picked up and enlarged from Fig.6.3.3.1-Fig.6.3.3.10. About 1^st voyage, NOx values were converted to net value because of above. As the emission value of monitoring results, the 1 Hr data are digitally averaged and are used for calculation of NOx emission (g/kWh).

.1 Engine performance data and calculation of NOx emission

 Engine performance data, analysis of fuel oil property, averaged NOx and O2 concentration and result of calculation of NOx emission are tabulated in Table 6.3.4.1-Table 6.3.4.3. Engine brake output power are calculated from engine performance data by the method which recommended by engine manufacture.

　

.2 Relation between engine load and calculation NOx emission

 Fig.6.3.4.1-Fig.6.3.4.3 show relation between engine load and ISO converted NOx emission in comparison with the data at shop trial for each voyage. And Fig.6.3.4.4. show all data gathered together.

　

 The data at sea trial with Marine Diesel Oil are about the same level as shop test data and lower than 17g/kWh. The sea trial data with Heavy Fuel Oil are lower than 19.55g/kwh which allowed in the NOx Technical Code for simplified measurement on board, but that are higher than shop test data by about 2g/kWh. In this test, Heavy Fuel Oil contained 0.37wt% of nitrogen. Assuming that 100%-50% of nitrogen in fuel is converted to NOx (Fuel-NOx), NOx emission increase about 2-1g/kwh. On the other hand, according to the fundamental test results (refer to capture 7.2), about 55% of nitrogen in fuel is converted to NOx. From above, it can be consider that not only Fuel-NOx but Thermal-NOx increase by flammable factor at operation with Heavy Fuel Oil.

　

 On all voyages NOx emission value are higher than shop test data and have big dispersion. About 70% of data exceed more than 15% of shop test data. (According to the provision of NOx Technical Code, the allowance 15% is accepted for E3 test cycle limitation, however. In this paper, "shop test result + 15%" line is drawn as a reference.) The range of dispersion is about 5% to 30% of shop test value. In most of data, NOx emission value is higher than that under assumption that 55% of nitrogen in fuel converts to Fuel-NOx. Therefore, thermal NOx problem cannot be bypassed.

　

 About 70% of data exceed more than 19.55g/kWh (17g/kwh+15%: allowance for simplified measurement on-board). From above, it can be consider that allowance for simplified measurement on-board of IMO NOx regulation is not enough. The cause of the difference between shop and on-board and the dispersion should be investigated and resolved further including effect of fuel property and operating condition of the engine.