The shift towards biofuels in 2024 has brought new dynamics to fuel quality and performance. The release of the updated ISO 8217:2024 specification now includes testing requirements for biofuel blends, reflecting the growing adoption of these fuels.
The Viswa Group issued its 2024 report on Global Fuel Characteristics, highlighting key trends in overall fuel quality, off-specification parameters across different regions, and the operational issues such as purifier sludging, fuel pump seizure, etc. affecting vessel performance.
Fuel Type Distribution in 2024
This section provides an overview of the distribution of various fuel types, including VLSFO, HSFO, LSMGO, HSMGO, ULSD, ULSFO, and biofuels. Figure 1 illustrates the fuel type distribution. An increase in the adoption of biofuels was observed in 2023 and 2024. Biofuels can help shipowners maintain or improve their vessel’s CII rating. As “drop-in” fuels, they can be used in conventional ship engines without requiring modifications, making them a practical option for achieving near-term GHG emissions reductions without significant investments in new ships or costly vessel modifications.
FIG 1 | Fuel type distribution in 2024
Characteristics of VLSFO vs. HFO vs. Bio-residual Fuels
Table 1 shows the minimum, average, and maximum values of the ISO 8217 parameters for VLSFOs, HSFOs and Bio-residual fuels in 2024 (off-spec samples not considered). This collected data shows that 2024 VLSFOs have lower viscosity, lower density, lower MCR, lower CCAI & higher calorific value in comparison to the HSFO.
TABLE 1 | VLSFO, HSFO and Bio-residual characteristics in 2024 (off-spec samples not considered)
Important points to note
- Overall, the quality of bio-residual fuels is similar to the VLSFOs, with lower average viscosity and lower net heat of combustion (approximately 3.4% lower calorific value). Most of the tested biofuels were B20-B35 samples.
- Average density, viscosity and MCR of VLSFOs are lower than HSFOs which shows that they are more paraffinic in nature.
- Net calorific value of VLSFOs is higher than HSFOs, which is due to the relative higher carbon content of VLSFOs in comparison to HSFOs.
Distribution of VLSFO characteristics by region – 2024
Density & Viscosity
FIG 2 | Density (Kg/m3) distribution of VLSFOs in 2024
FIG 3 | Viscosity (cSt at 50C) distribution of VLSFOs in 2024
Stability properties
One of the main challenges with VLSFOs is the stability of these fuels. They are made from a diverse range of blending stocks varying from highly paraffinic to highly aromatic. When mixing two fuels, one paraffinic and one aromatic, which are stable by themselves, the resulting mixture might become unstable. Therefore, the result will be excessive sludging because of asphaltene deposition. Figure 4 shows the distribution of the sediment content of VLSFOs from different regions. Fuel stability data from different regions, expressed through Total Sediment Potential (TSP) shows that fuels from Houston, ARA, and New York have the highest number of samples with off-spec sediment values. In addition, Hong Kong had the highest number of samples with sediment content in the borderline stable range (0.06-0.1%).
FIG 4 | Distribution of the sediment content of VLSFOs from different regions
Catfine (Al & Si content)
Catfines (Al and Si compounds) are hard abrasive particles that remain in fuel oil as a by-product resulting from the catalytic cracking technology or fluid catalytic cracking (FCC) used in the intensive refining and blending process to reduce the sulfur content. The average catfine content of all the regions are below the limit of 60 ppm as per ISO8217 specification. Houston and Singapore have the highest average catfine content.
FIG 5 | Catfine distribution in different regions and major ports
VLSFO characteristics in 2024
Off spec parameters
In 2024, 4.3% of the VLSFO samples tested by Viswa were found to be out of the ISO 8217 specification. Table 2 shows the percentage of VLSFOs that did not comply with ISO 8217 parameters across different regions. The primary off-spec parameter in Africa, and Asia was sulfur content. In North America and Europe, sediment content was the main issue, while in Oceania, off-spec water content samples were the highest. In South America, the highest percentage of off-spec parameters was related to acid number.
TABLE 2 | Percentage of off-spec parameters across different regions
Fuel characteristics in 2024
Off spec parameters
Off spec parameters
VLSFO characteristics in 2024
Operational issues
The main operational issue related to VLSFOs in 2024 was instability. Nearly 60% of the problem cases reported to Viswa were Purifier choking/ Purifier choking & Filter choking, because of the instability issues. There were cases where the VLSFO met the ISO8217 specification limit for the sediment content (TSP & TSA) at the time of bunkering and then became unstable within a matter of weeks. This constitutes the shelf life of the VLSFO.
FIG 8 | VLSFOs problem in 2024
VLSFO operational issues in 2024
Sludging issues
60% of problem cases reported to us in 2024 were related to purifier sludging and filter choking. VLSFO sludging issues was not only related to the samples with high sediment content on day 1 of testing but also related to the samples in which the sediment content on day 1 was within the specification of ISO8217 (0.1%). After two to four weeks of storage or usage of the fuel the sample became unstable and sediment increased to higher than 0.1%. Total sediment potential or Total sediment accelerated are not a guarantee for long term stability properties of VLSFOs. Fig 9 shows nine samples with low sediment content on day 1 of testing which became unstable after a few weeks of usage and storage of the fuels and resulted in to the purifier choking and sludging issues.
Table 3 highlights the characteristics of several unstable fuels that led to sludging issues. An interesting observation is that in most cases, sediment content, TSP, and TSA are elevated when sludging occurs. In approximately 20% of the cases, the difference between the TSP and TSA values is notable, with the TSP being 0.1% higher than the TSA. Additionally, the majority of these sludging problems are associated with low-viscosity VLSFOs, with viscosities below 100 cSt.
Fuel pump issues
Based on our problem fuel data in 2023 and 2024, there was a notable increase in fuel pump problems, marking a rise compared to 2022. This trend is likely attributed to the use of new complex blending streams with higher concentrations of chemical contaminants in the production of Very Low Sulphur Fuel Oil (VLSFO).
In 2024, fuel pump problem cases involved fuel pump corrosion, sticking and seizure, pressure drops, and reduced Pmax levels. Additionally, some incidents reported purifier clogging and elevated exhaust gas temperatures.
The three major cluster of cases were associated with fuels bunkered in the following regions:
1. US Gulf Coast ports
2. ARA (Amsterdam-Rotterdam-Antwerp) region
3. Malta ports
Problem fuels from US Gulf Coast
In 2024, we received reports of fuel pump-related issues from nine vessels that had bunkered in Houston, Bolivar Roads, Barbours Cut, and New Orleans. The contaminated fuels were associated with fuel pump malfunctions, corrosion and, in some cases, purifier sludging and filter choking. For all nine samples, the ISO 8217 parameters were within acceptable limits. However, GCMS analysis revealed the presence of uncommon chemical compounds, including 2-Ethylhexanol, Tetrachloroethylene, FAME, and free fatty acids.
While these compounds may not directly cause operational issues, their presence at some elevated levels serves as an indicator of contaminated VLSFO bunkers originating from US Gulf ports. Please also note that only in VLSFOs, the presence of these fingerprint compounds have been associated with problems. We tested some HSFOs and ULSFOs with the same fingerprint chemical compounds and the vessel was able to use the fuels without any problem. We are still investigating the root cause of these problems.
Problem fuels ARA
In 2024, we encountered fuel contamination issues across 11 bunkers supplied within the ARA regions, which included 2 fuels from Antwerp, 8 from Rotterdam, and 1 from Amsterdam. These fuels all presented with operational challenges, such as excessive wear, fuel pump issues, purifier sludging, and filter choking. The affected fuels consisted of 8 VLSFOs and 3 HSFOs.
While the ISO 8217 parameters of the fuels were within normal specifications, GCMS analysis identified elevated levels of multiple contaminants in the affected samples. Of particular concern, 4 of the problematic cases had Cardanol concentrations exceeding 10,000 ppm. This compound, which has also been detected in fuels supplied within the ARA region in 2023, is indicative of the presence of cashew nut shell liquid in the fuel.
Furthermore, the remaining 7 problematic samples exhibited high concentrations of phenolic compounds, including Resorcinol, 2-Methylresorcinol, 5-Methylresorcinol, 2,5-
Dimethylresorcinol, C2 Phenols, C3 Phenols, and others. Some samples also contained ketonic compounds. It is important to highlight that the presence of phenolic compounds, particularly in substantial quantities, can lead to increased sludging, which may cause fuel pump seizure due to the sticky nature of the sludge generated by these compounds.
Problem fuels Malta
From July to September 2024, four problem samples reported to us were related to fuel pump issues and some cases of sludging. These samples were supplied by different suppliers. Of the four VLSFO samples, three exhibited fuel pump seizures, while one experienced excessive sludge accumulation in purifiers.
The ISO 8217 parameters for these fuels were within the normal limits. However, the total acid number (TAN) for these fuels was higher than the average for Malta, although still within the ISO 8217 specification limit of 2.5 mg KOH/g. Additionally, the total sediment potential in two of the samples was elevated, at 0.07%.
GCMS analysis of these problem samples identified the presence of phenolic compounds (e.g., 2-Methylphenol, 2-Ethylphenol, C3 Phenols) in concentrations ranging from 1,000 to 2,000 ppm, alcohol-based compounds (e.g., 1-Phenylethanol, 2-Phenylethanol, 1-Phenoxy-2- propanol, 2 Phenoxy-1-propanol) between 2,000 and 4,000 ppm, and free fatty acids ranging from 362 to 530 ppm. Additionally, unknown oxygenated compounds were detected, along with aromatic acids such as benzoic acid.
Further testing revealed that the oxygen content of these problematic samples ranged from 0.7% to 1%, which is higher than the average for VLSFOs (typically below 0.5%). These findings, combined with the GCMS results, suggest the presence of oxygenated compounds in the samples. Our data indicates that oxygenated compounds, such as ethers or ketones,
are prone to oxidation, leading to gum formation, which can result in sludging and fuel pump seizures, particularly at elevated temperatures.
HSFO-MGO characteristics in 2024
Operational issues
Bio-Fuel characteristics in 2024
Biofuel operational issues
distillate 2 conducted as per ASTM D665.
In 2024, we received reports of issues from three vessels using biofuel blends. Two of the samples (Bio-residual 1 & Bio-distillate 1) met ISO 8217:2017 specifications, but the tested FAME content did not match the designated fuel grades.
The third sample (bio-distillate 2) showed an acid number of 20 mg KOH/g and a FAME content of only 4%. Investigative GCMS analysis on Bio-distillate 2 identified contamination with high levels of free fatty acids. Copper corrosion test on this sample showed a rating 1a.
A steel corrosion test1 was conducted in accordance with ASTM D665. The rod was found to be fully rusted, likely due to oxidation and corrosion processes. This outcome is expected, as the acid number of the sample is considerably high and contains significantly high concentration of free fatty acids.
As a result, one of the important tests for biofuel blends is testing the FAME content of fuels. Testing FAME content is crucial to ensure it complies with the specified fuel grade. In case of usage of new types of biofuels with Non-FAME feedstock, please ensure detailed testing and trials before the usage onboard the vessel.
1 The steel corrosion test, conducted as per ASTM D665, does not fully replicate vessel conditions for fuels and has been used solely for investigative purposes.
Source: The Viswa Group
