Since January 2015, ships operating in the SECAs have had to use marine fuels with a maximum FSC of 0.1 %m/m. Previously, the limit was set to 1.0 %m/m S. Starting in 2020, the allowed FSC will be 0.5 %m/m at global level (see section 2.3). This reduction will have an impact on particle emissions. However, few studies have focused on operating ships or test-bed engines running on low-sulphur marine fuel oils (see references in Paper I). Furthermore, one of the driving forces behind the regulation of the FSC both in ECAs and at the global level was the goal of reducing particle emissions. The regulation of FSC forces ship owners to run their ships on low- sulphur marine fuel oils, use alternative fuels with a FSC that complies with the regulation or use scrubbers. This thesis focuses on the first two alternatives: use of low- sulphur marine fuel oils (Paper I and Paper III) and alternative fuels, in this case liquefied natural gas (LNG) (Paper II), and the impact of other fuel characteristics,
such as content of aromatics, on the particle emissions (Paper IV) (Figure 2-3). Furthermore, because emissions of SOX and NOX are regulated in the revised MARPOL Annex VI, interest has shifted towards particle emissions and CO2.
Figure 2-3: Overview of the four studies included in this thesis.
The study presented in Paper I was developed and designed with the regulation of FSC in mind. The two marine fuel oils studied have a FSC that complies with current and future legislation: HFO (0.12 %m/m S) in SECAs and MDO (0.52 %m/m S) at the global level. Emissions from the combustion of Swedish environmental class 1 diesel (MK1, <3 ppm S) and Swedish environmental class 3 diesel (MK3, 3 ppm S) were studied as well. The objective was to gain increased knowledge of the impact of FSC and other fuel characteristics on particle emission. The measurements were done when the engine was operating at lower engine loads, in order to approximate the emissions from ships operating in port areas.
In Paper II, particle and gaseous emissions from a ship using LNG for propulsion was studied. LNG is regarded as a potential future marine fuel, both from environmental and economic perspectives. This may be the first study conducted on-board a ship running on LNG that includes data on the number of particles emitted as well as particle mass and gaseous emissions. This was a unique opportunity for data collection. The study in Paper III presents results from measurements made on-board the same ship and the same engine before and after January 2015. The two fuel types investigated are normally used for propulsion of the ship and had been used for a period of time before the measurements were made. The two studied fuel types were a HFO with 0.48 %m/m S (used before January 2015), and a low-sulphur residual marine fuel oil (RMB30, 0.092 %m/m S, used after January 2015). The RMB30 oil is a so-called hybrid fuel (described in section 3.2) and is an alternative to marine gas oil (MGO) for ships operating in SECAs. The objective with this study was to investigate how the reduction in FSC affected the particle emissions from a ship operating under normal conditions with normally used fuel types.
Because the FSC for marine fuel oils is regulated, it is interesting to consider which other fuel characteristics that could be changed to further reduce the emissions of particles from ship operations. In Paper IV, the content of aromatics in the fuel was investigated. The content of aromatics was chosen because aromatics are soot precursors in the combustion process (Bockhorn, 1994). Furthermore, few other
studies have considered the number and sizes of particles emitted from fuel-blends with various contents of aromatics. Previous studies have mainly focused on the mass of particles emitted. However, no consensus was reached in earlier studies, because some studies showed an increase in PM with aromatic content and others showed no effect on PM with varying aromatic content (see references in Paper IV). The measurements were done on test-bed engines at the Department of Shipping and Marine Technology and at the Department of Applied Mechanics, Chalmers University of Technology. In the studies, MK1 was used as the reference fuel, though it has a low content of sulphur and other compounds that may enhance the formation of particles. To achieve a high content of aromatics, MK1 was doped with a solution of aromatics to levels comparable to those found in marine fuel oils.
There is also interest in studying the impact on BC emissions from marine fuel oils. There is an on-going discussion within the IMO, with the aim of establishing a future regulation of BC emissions from operating ships. The emissions of BC are believed to be related to fuel characteristics other than the FSC (discussed further in section 5.2) (Lack et al., 2009, Lack et al., 2011). Therefore, further research on this should be of interest. The results from measurements of BC emissions have been included in Paper I, in which the FSC of the HFO is lower than the MDO, thereby making it possible to investigate if other fuel characteristics are more important than FSC. The results of the BC measurements are also included in Paper III to describe how the fuel shift towards fuels with lower FSC affects the emissions of BC. Furthermore, this study provides an indication of whether a reduction in FSC is enough to reduce the BC emissions or whether other compounds in the fuel must be considered as well.
The papers included in this thesis include measurements and data on the PN emissions and size distribution by number. During the work on the different papers, the focus has more or less turned towards a focus on the number and sizes, rather than on the PM emissions. This is because particle size is one of the most important properties in the assessments of the impact of particles on human health (section 2.1). Therefore, measurements of the size distribution based on the number of emitted particles are important. Furthermore, the importance of considering PN concentrations is highlighted in Kittelson (1998). Measuring the number and sizes of particles emitted from ship operations is quite a new field, and in contrast to land-based transportation, there remains a lack of knowledge. The EFs (EFPN andEFPM,together with size- resolved EFs) presented in the included papers are useful data in emission inventories, environmental impact assessments and dispersion modelling. Furthermore, the EFs provide an opportunity to compare particle emissions from low-sulphur marine fuel oils and LNG with emissions from marine fuel oils with other properties and emissions from other transport sectors.
3 Marine Engines and Marine Fuels
The most common marine engines installed on-board ships are marine diesel engines that use various marine fuel oils for propulsion. The most common marine fuel oil is HFO due to its low price. However, the current regulation of FSC in SECAs force ship owners to use marine fuel oils with low FSCs (max. 0.1 %m/m S), alternative fuels or scrubbers. One alternative fuel of interest is LNG because it is economically feasible compared to marine fuel oils. The aim of this section is to provide an overview of the marine engines and marine fuels considered in the papers included in this thesis. Furthermore, information on certain fuel characteristics discussed in this thesis are included as well.