Modelling Low Sulphur Fuel Oil Weathering

The main objective of the IMAROS task 3.5 “modelling the weathering of low Sulphur fuel oil” was to
demonstrate the ability or the inability of the existing oil weathering parameterizations to predict the
weathering of the new fuel oil types. In case the current parameterizations turn out to be inaccurate,
new parametrizations had to be suggested. Finally, since each European countries operate their own
oil spill drift, fate and behavior model, the findings and conclusions of this task had to be reported
independently of these models but as best practices that could be implemented in the different
national models.

To achieve all these objectives, a 3-step methodology was followed. First, a literature review has been
performed to identify the state-of-the-art oil weathering parametrizations. Then, the selected
weathering parameterizations were implemented in a so-called “toy model” (i.e., a light 0D oil
weathering model whose only purpose was to play with the implemented weathering
parameterizations). Finally, the toy model results were validated / invalidated against observations
from several experiments carried out at CEDRE’s polludrome (tank filled with water able to simulate
the weathering of oil at sea).

The present reports strictly follow this 3-step approach. In section 2 , we define the concept of oil
weathering and give a comprehensive introduction to the concept of weathering model and
weathering process parametrizations. Interested readers shall find the equations of the weathering
processes parametrizations in Annex I. In section 3, we present the physicochemical characteristics of
the LSFO oils tested in the framework of the IMAROS project. 13 oils referred as IM1 to IM13 have
been initially tested in Lab. Their properties were quite diverse, for instance with a pour point ranging
between -27°C and +30°C. In a second step, weathering of 3 VLSFO oils have been tested at pilot scale
(flume tank). This report focuses on these 3 oils referenced as IM-5, IM-14, and IM-15. In section 4, we
present the numerical experiences we performed with our toy model to simulate the oil weathering
as in CEDRE’s flume tank. In section 5, we compare and discuss the model simulation results with the
observation in CEDRE’s flume tank. Finally, in section 6, we draw some conclusions and present some
recommendations in the form of best practices.