IMO: classification and specification of marine fuels

The International Maritime Organization on 13 December 2023 published the document providing an informative indicator to determine whether fossil fuels not containing fatty acid methyl esters (FAME) lean towards being paraffinic or aromatic in nature.

Introduction

This document provides the outcome of the work undertaken by ISO/TC 28/SC4/WG6 to provide an informative indicator to determine the nature of residual marine fuels.

Document PPR 8/5/1 (Finland and Germany) provided the final results of a testing campaign aimed at studying the impact of the quality of very low sulfur fuel oils on Black Carbon (BC) emissions.

Even though it is recognized in document PPR 8/5/1 that the tested fuels might not be representative for the global market share, paragraph 37 proposed the implementation and limitation of the aromatic content or H/C ratio in marine fuels and requested the International Organization for Standardization (ISO) to review ISO 8217 to include specifications that consider the results of the study.

Discussion

ISO/TC 28/SC 4/WG6 has reviewed the options to provide the marine industry with an informative indicator and to have a consistent approach to the characterization of the nature of residual marine fuels, including very low sulfur fuel oils (VLSFO).

In its discussion, the methodology using the Bureau of Mines Correlation Index (BMCI/CI) and the methodology using the Viscosity Gravity Constant (VGC), as well as the H/C ratio, were considered.

ISO/TC 28/SC 4/WG6 agreed to apply established guidance used by the petroleum industry to characterize fuels in terms of their paraffinic to aromatic nature.

The ASTM publication "Characterization and properties of petroleum products" by M.R. Riazi was therefore selected as the most established and applicable reference document to base the approach on.

This document makes reference to the Bureau of Mines Correlation Index (BMCI/CI) and the Viscosity Gravity Constant (VGC), both of which provide an indication of a fuel's tendency to be more paraffinic or aromatic, with VGC providing a simpler approach using the viscosity and the density of the fuel which are already routinely being measured as part of the fuel quality control testing.

The calculation of VGC is also published as a standardized test method, that being ASTM D2501.

The inclusion of the H/C ratio in ISO 8217 was not supported by ISO/TC 28/SC 4/WG6.

Today, very little test data on the H/C ratio of marine fuels is available to allow assigning a reference value for what would be considered to be a more aromatic or paraffinic marine fuel.

There is today no operational or regulatory need to measure C and H content of a marine fuel and, therefore, placing the H/C in ISO 8217 would not necessarily result in the H and C tests being carried out.

Furthermore, the H/C ratio is the result of the fuel blend composition and fuel suppliers are not targeting a specific H/C ratio, which would be very difficult to do.

The work undertaken by ISO/TC 28/SC 4/WG6, published as ISO/TR 18588:2023 Petroleum products – Characterization of marine fuels by viscosity-gravity constant, shows that not only VGC but also density, which is an already measured property of marine fuels, can be used as an indicator for the nature of the fuel.

VGC values near 0.80, or density near 900 kg/m3 are indicative of the fuel being more paraffinic in nature, while a VGC near 0.92 or higher, or density near 990 kg/m3 or higher are indicative of the fuel leaning towards being more aromatic in nature.

The seventh edition of ISO 8217 will include an informative annex on the characterization of residual marine fuels using VGC.

Published version of ISO/TR 18588:2023

A copy of the published technical report, ISO TR 18588:2023, is set out in document PPR 11/INF.7 (ISO).

Action requested of the Sub-Committee

The Sub-Committee is invited to consider the information provided in this document in combination with the information set out in document PPR 11/INF.7, and take action as appropriate.

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