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Study raises concerns about black carbon emissions from VLSFO marine fuels

28 January 2020

A study submitted to the IMO’s Pollution Prevention and Response (PPR) sub-committee has generated significant media attention by raising the possibility that some 0.5% sulfur VLSFO marine fuel may lead to increased black carbon emissions. The authors of the study recommend introducing either an H/C ratio or aromatic limit in ISO 8217 to limit the amount of aromatics in VLSFO while a number of NGOs have called for changes to MARPOL Annex VI to prohibit the use of low sulphur heavy fuel oil blends that increase black carbon emissions and a requirement that only distillate fuels be used in the Arctic.

In this study, fuels having aromatic content of 70-95% were shown to emit 10% to 85% more black carbon than HFO with 50% aromatics.

However, the focus of the study was to further develop black carbon measurement methods as part of the work on reducing the impact of shipping on black carbon emissions in the Arctic. It was not clear whether the range of fuels tested actually represented realistic fuels that would be available after January 1, 2020.

Measurements were carried out on a single cylinder version of the MAN 32/44CR-TS medium speed engine at the 4 modes of the ISO 8178 E2 cycle. The engine represents the newest technologies for medium speed marine diesel engines and includes electronic injection, two-stage high efficiency turbochargers, electronic hardware, and variable valve timing. The test cycle is carried out at four different loads at constant rated speed and is representative of diesel-electric drive or variable-pitch propeller installations.

The work was conducted by the German non-profit research institute WTZ Roßlau and was assisted by MAN ES, DNV GL and Marena Ltd. The project was funded by the German Environment Agency. The results of the study were cited in a submission made by Finland and Germany to the IMO’s Pollution Prevention and Response (PPR) session scheduled for February (PPR7). The study is dated November 15, 2019 and the work would have been completed before it was clear what fuels would be available after January 1, 2020. The study as well as the response from some NGOs are available from the IMO webaccounts.imo.org (registration is required).

According to the International Bunker Industry Association (IBIA), “The transition to 0.50% sulphur fuels is still in its early days and to the extent of IBIA’s knowledge there is no comprehensive overview available at this stage that documents the actual variability and quality of such fuels on the market. Early indications from several fuel testing agencies do, however, indicate that 0.50% sulphur fuels seen so far tend to be more paraffinic and less aromatic than the HSFOs they have replaced. As such, it seems premature to draw any valid and meaningful conclusions on the level of black carbon emissions associated with the use of 0.50% sulphur fuels.”

Low sulfur blend components high in aromatics likely to be used in blending VLSFO include fluid catalytic cracking (FCC) components light cycle oil (LCO) and slurry oil. Slurry oil that has cat-fines removed is sometimes called clarified oil (CLO). LCO is mainly composed of 1- and 2-ring aromatic while CLO of 2-to 5-ring aromatics [4275].

According to Argus Media, fuels with more than 50% aromatics are most likely to be produced by blending low sulfur residue with LCO and slurry oil. Low sulfur residue is obtained from sweet crudes or after desulfurization of residue from sour crudes.

The correlation of fuel properties to emissions is challenging. Prior to the early 2000s, much work was done to understand which fuel properties affected emissions—especially from heavy-duty engines. While fuels with higher aromatics often correlated with higher PM emissions, the cause of higher PM was not necessarily due to higher aromatics. A number of other fuel properties such as ignition quality and fuel density are also affected that can change combustion and fuel injection system behaviour that ultimately is the dominant factor. Some engines can be quite sensitive to fuel property variations while others are not. Aromatic limits in some diesel fuel specifications such as CARB diesel and EN 590 where introduced in this era in an attempt to limit emissions.

Source: IMO Documents: PPR 7/8