Hello Queseanians,
Fuel safety remains a critical and longstanding concern.
Recently, I’ve been thinking a lot on this issue, particularly in light of the urgent need to reduce emissions from the shipping industry, which has led to discussions about various fuel options. While the focus often is given on the flashpoint of fuels, it’s essential to recognize that there are several other important factors that need careful consideration.
Understanding the Importance of Fuel Quality
Ensuring high-quality bunker fuel is crucial for the safety of ships, their equipment, and the environment. Poor-quality fuel can lead to various issues, such as instability, chemical contamination, and inadequate performance in cold conditions.
Common Concerns with Fuel Quality
Some frequent problems with bunker fuel include:
- Instability
- Chemical contamination
- Corrosive properties
- Inefficient combustion
- Cold flow issues
While bunker fuel quality has been generally stable in recent years, it is essential to understand that fuel quality assessments often refer to the criteria set in the ISO 8217 standard. Unfortunately, there have been instances where fuel that meets these standards has still caused significant problems onboard due to its poor quality.
Recently, there has been an increase in operational issues related to contaminated fuels that standard tests may not detect. This rise can be linked to efforts towards reducing emissions, particularly with regulations like Sulphur cap 2020, which have prompted fuel suppliers to explore new blending options with traditional fossil fuels.
Monitoring Cold-Flow Properties
The cold-flow characteristics of fuel are particularly important when operating in colder climates. It is essential to keep an eye on the Pour Point of Heavy Fuel Oils (HSFO), Very Low Sulfur Fuel Oils (VLSFO), and Marine Gas Oil (MGO) when sailing in cold regions. In 2023, Pour Point was the leading reason for MGO failing quality standards, accounting for 36.6% of off-spec cases. To minimize the risk of solidification, it is generally advised to maintain the fuel temperature at least 10°C above the Pour Point.
The following table provides a comprehensive overview of fuel properties along with associated hazards and challenges. These factors are critically important for assessing the safety and usability of fuels, particularly in relation to meeting the 0.50% m/m global fuel oil sulfur limit.
Fuel Property | Potential Challenges | Remarks |
---|---|---|
Stability | The consequences of a ship receiving an unstable fuel, or one that becomes unstable during storage or handling, can be serious. Sludge may build up in the storage tanks, piping systems or centrifuges and filters can become totally blocked by voluminous amounts of sludge. | The challenge for the fuel producer is to blend a fuel which is not only stable but also has a degree of reserve stability such that it will remain stable during periods of storage and treatment at elevated temperatures. More paraffinic blend components are expected for Very ow Sulphur Fuel Oil (VLSFO) compared to existing fuels. Whereas aromatic components have a stabilizing effect on asphaltenes, paraffins do not. Fuel suppliers are responsible for ensuring that the supplied fuel is stable. |
Compatibility issues | Challenges are the same as with stability (above). | An incompatible mix may be harmful to ship’s operation. VLSFOs are expected to be paraffinic based in some regions and aromatic based in other regions. There is a risk of experiencing incompatibility when mixing an aromatic fuel with a paraffinic fuel. The same risk exists today, but with the wide range of products which may exist post 2020, it is important to segregate fuels as far as possible and to be cautious of how to manage/handle incompatible fuels on-board. |
Cold flow properties | ISO 8217 limits the cold flow properties of a fuel through setting a limit on the pour point (PP). However, given that wax crystals form at temperatures above the PP, fuels that meet the specification in terms of PP can still be challenging when operating in colder regions. Wax particles can rapidly block filters, potentially plugging them completely. The paraffin’s may crystallize and/or deposit in the storage tanks leading to blockages at the filters and reduced fuel flow to the machinery plants. | VLSFO products are expected to be more paraffinic compared to existing fuels. As such, it is important to know the cold flow properties of the bunkered fuel in order to ensure proper temperature management on-board. It is important to note that for additives to be effective, they have to be applied before crystallization has occurred in the fuel. |
Acid number | The fuel shall be free from strong, inorganic acids. Fuels with high acid number test results arising from acidic compounds cause accelerated damage to marine diesel engines. Such damage is found primarily within the fuel injection equipment. | There is currently no recognized correlation between an acid number test result and the corrosive activity of the fuel. ISO 8217:2017, appendix E covers the topic. |
Flashpoint | Flashpoint is considered to be a useful indicator of the fire hazard associated with the storage of marine fuels. Even if fuels are stored at temperatures below the determined flash point, flammable vapours may still develop in the tank headspace | |
Ignition and combustion quality | Fuels with poor ignition & combustion properties can, in extreme cases, result in serious operational problems, engine damage and even total breakdown. Poor combustion performance is normally characterized by an extended combustion period and/or poor rates of pressure increase and low p max resulting in incomplete combustion of the fuel. The resulting effects are increased levels of unburned fuel and soot that may be deposited in the combustion chamber, on the exhaust valves and in the turbocharger system, exhaust after treatment devices, waste heat recovery units and other exhaust system components. Extended combustion periods may also result in exposure of the cylinder liner to high temperatures which may disrupt the lubricating oil film, leading to increased wear rates and scuffing. Unburnt fuel droplets may also carry over impinging on the liner surfaces causing further risk of damage to the liner. | High and medium-speed engines are more prone to experience operational difficulties due to poor ignition and combustion properties than low speed two stroke types. With four stroke engines, poor ignition can result in excessive exhaust gas system deposits, black smoke, engine knocking and difficulties operating at low load. If the ignition process is delayed for too long a period by virtue of some chemical quality of the fuel, too large a quantity of fuel will be injected into the engine cylinders and will ignite at once, producing a rapid pressure d eat rise and causing associated damage to the piston rings and cylinder liners of the engine. |
Cat fines | Cat fines will cause abrasive wear of cylinder liners, piston rings and fuel injection equipment if not reduced sufficiently by the fuel treatment system. High wear in the combustion chamber can result. | Major engine manufacturers recommend that the fuel’s cat fines content does not exceed 10 mg/kg (ppm) at engine inlet. |
Low viscosity | Low-viscosity fuels (less than 2cSt at engine inlet) challenge the function of the fuel pump in the following ways: .1 breakdown of the oil film, which could result in seizures; .2 insufficient injection pressure, which results in difficulties during start-up and low-load operation; and .3 insufficient fuel index margin, which limits acceleration |
Low fuel viscosity does not only affect the engine fuel pumps. Most pumps in the external fuel oil system (supply pumps, circulating pumps, transfer pumps and feed pumps for the centrifuge) also need viscosities above 2cSt to function properly. Viscosity is highly temperature dependent, and the crew must take proper care of fuel oil temperature management to avoid viscosity related issues. |
Pour point | If fuels are held at temperatures below the pour point, wax will begin to precipitate. This wax may cause blocking of filters and can deposit on heat exchangers. In severe cases the wax will build up in storage tank bottoms and on heating coils, which can restrict the coils from heating the fuel (fuel will become un pumpable from the bunker tanks). | |
Unusual components (possibly related to blending) | The below components and group of components can be linked to the risk of encountering the following problems: · Polymers (e.g. polystyrene, polyethylene, polypropylene): Associated with filter blocking · Polymethacrylates: Cause fuel pump sticking · Phenols Occasionally: Associated with filter blocking/fuel oil pump sticking · Organic acids: Have led to corrosion as well as fuel pump sticking · Chlorinated hydrocarbons Associated with fuel pump seizures · Tall oils: Associated with filter blocking · Estonian shale oil: Associated in the past with excessive separator sludging |
Do you have any similar concerns or thoughts to share with me?
References:
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MAN Service Letter SL2014-593/DOJA
sl2014-593.pdf (598.8 KB) -
MSC 100/8/2
MSC 100-8-2 - Safety implications and respective challenges associated with 2020 compliant fuels (Bahamas, Liberia, Marshal…).pdf (41.6 KB)