|
7.3 Conversion rate from nitrogen in fuel to fuel-NOx
Further tests with CVCC for other samples from three monitored ships have been carried out. Fig. 7.3.1 shows the result. Alphabet of each sample is the initial of the monitored ship's name. Considering the preliminary test results, heat release rates of all the samples were measured beforehand and only the NOx data of the samples with similar heat release rate were adopted. For example, the sample 'BFO-A' with the highest nitrogen (0.87%) in this figure, that was not from the monitored ship but specially prepared for this experiment, showed a longer ignition delay and a higher peak of pre-mixed combustion than the others at the heat release rate measurement. So, this data was not included to count the conversion rate to fuel-NOx.
According to Fig. 7.3.1, most of the data have little deviation from 'Conversion Rate 55% Line' proposed in Fig. 7.2.3 at the preliminary test. Assuming the conversion rate, fuel-NOx in the exhaust gas can be estimated with following calculation.
Fuel-NOx (NO2) g/kWh = SFC ・ N ・ R ・ (46/14)
SFC = specific fuel consumption
N = nitrogen %/100 in the fuel
R = N to fuel-NOx conversion rate
Molecular weight of nitrogen is 14 and NO2 is 46.
Fig. 7.3.2 shows recent nitrogen % data in bunker fuels from various ports reported by NK. According to it, bunker fuels from Long Beach contain higher N% than the others. (The sample 'BFO-A' with 0.87% nitrogen was also from the West Coast.)
As an example. applying a data, 0.7% of nitrogen from Long Beach and assuming 180g/kWh of SFC and 55% of conversion rate to the above-mentioned formula, fuel-NOx can be estimated at about 2.3g/kWh. This value becomes no less than 14% of 17g/kWh, limited value by IMO. Considering such the case, it must be brought up for discussion again if 15% allowance for the on-board measurement is enough or not when bunker fuel is burned.
Fig. 7.2.1 Constant volume combustion chamber(CVCC)
Fig. 7.2.2 NOx measuring procedure for CVCC
Sampling
Analysis
Table 7.2.1 Properties of sample fuels
| |
MDO |
I-1 |
I-2 |
A-1 |
High N |
| Density(@15℃) |
kg/m3 |
843 |
976 |
968 |
1007 |
988 |
Kinematic
Viscosity(@50℃) |
mm2/s |
2.5 |
381 |
372 |
472 |
350 |
| Sulphur |
wt% |
0.4 |
3.3 |
3.0 |
3.1 |
3.5 |
| Nitrogen |
wt% |
0.02 |
0.34 |
0.39 |
0.3 |
0.66 |
| Water |
wt% |
|
< 0.1 |
< 0.1 |
< 0.1 |
0.1 |
| Ash |
wt% |
|
0.03 |
0.05 |
0.01 |
< 0.1 |
| Residual Carbon |
wt% |
0.1 |
15 |
13 |
17 |
15 |
| Asphaltene |
wt% |
|
7.0 |
6.2 |
8.4 |
|
Lower
Calorific Value |
MJ/kg |
42.5 |
40.34 |
40.53 |
39.99 |
40.05 |
| CCAI |
- |
(811) |
837 |
830 |
866 |
850 |
| Bunker Port |
|
|
Fujairah |
Fujairah |
Rotterdam |
|
|
Fig. 7.2.3 Result of preliminary test with CVCC
Fig. 7.2.4 Heat release rates of sample fuels
(a)
Time from injection start(ms)
(b)
Time from injection start (ms)
Fig. 7.3.1 Further test result using CVCC
|
Fig. 7.3.2
|
Nitrogen % in bunker fuels from various ports
|
|
