*3.3. Particle Composition*

Filter samples of particles from two of the tested engine load points are analysed for composition. Our results indicate that also solid particles are removed during the scrubber process. An efficient removal of EC is seen at the high engine load. The removal of EC at the tests at low engine loads appear to be higher still, although tests upstream were made at 32% and tests downstream at 41% engine load, which could possibly exaggerate the effect seen. At LSFO combustion, the organic carbon dominates particle mass at both engine loads. Sulphates are not significantly contributing to particle mass and constitute 1.2% and 2.7% of total mass at 34% and 75% engine load, respectively. The particles from HFO downstream of the scrubber are similar in composition at the two loads tested. Upstream of the scrubber both organic and elemental carbon contribute significantly to particle mass, especially at the lower engine load. Sulphur is more abundant in particles at the higher load in the upstream tests. The absolute and relative contributions of components are presented in Table 4 and Figure 6. The undefined mass of particles at the respective test conditions varies between 1% and 25%.

### *3.4. E*ff*ects of Sampling System Parameters*

Sampled particles (PM) include all solid and condensed material present in the diluted and cooled diesel exhaust. The composition can be expected to change throughout their passage in the exhaust duct and during the sampling due to changing conditions. The PM, both in terms of mass and number concentration, are sensitive to variations in temperature and humidity in the exhaust and during the sample conditioning (dilution). In the scrubber, the gases are cooled from around 300 ◦C to around

20 ◦C using water that is added to the exhaust as part of the scrubber design. Water that remains in the exhaust is removed with a demister system as part of the scrubber design. In the hot exhaust tests on HFO, upstream of the scrubber, we followed the ISO 8178 for dilution and sampling with a few exceptions. The standard is not applicable for cold exhaust gas sampling and an alternative sampling system was used downstream of the scrubber. Downstream of the scrubber, the sample line is heated, and the dilution is first made with hot and then ambient-temperature air. The temperature influences the volatile content of particles to a grea<sup>t</sup> extent. Detailed analysis of emission factors for PM mass sampled with the dilution tunnel and with FPS shows a grea<sup>t</sup> deal of variability, especially for the low engine load emission factors. The variability is, however, not only between the two dilution devices, but also within the samples taken with the same device. The variability is larger for HFO tests upstream the scrubber where a large influence of condensable sulphate is expected. Development of a robust sampling methodology for testing of emissions of particulate matter in the exhaust of widely varying physical and chemical properties is an important subject for further research.

**Figure 5.** Specific emissions of US EPA's PAH-16 (**a**) and PAH-7 (**b**) at HFO and downstream of the scrubber and at LSFO combustion.



1 sulphate calculated from analyses of S on filters, H2O calculated as SO4 2−\*0.8, see [14]; 2 average at test conditions (considering dilution ratio) from gravimetric analysis on filter.

**Figure 6.** Absolute and relative contributions of particulate components to particle mass at different tests. N.B. analysis of filters from similar sampling and dilution conditions are considered, and total PM values may differ from the average values given in Table 2.
