Density
Density gives an indication of the ignition quality of the fuel within a certain product class. This is particularly the case for the low-viscosity IFOs. The product density is important for the onboard purification of the fuel; the higher the density, the more critical it becomes.
Separator operation is critical and not possible using a purifier with a water seal. Operating the separators as clarifiers may reduce cat fines and sediment but most likely not water. Optimum adjustment of the separators is important for efficient fuel treatment.
Viscosity
Kinematic viscosity is a measure for the fluidity of the product at a certain temperature. The viscosity of a fuel decreases with increasing temperature. The moment the fuel leaves the injectors it must be within the limits prescribed by the engine manufacturer to obtain an optimal spray pattern. Viscosity outside manufacturers’ specifications at the injectors will lead to poor combustion, deposit formation and energy loss. The viscosity of the fuel must be such that the required injection viscosity can be reached by the ship’s preheating system.
Pour Point
Pour point is the lowest temperature at which a fuel will continue to flow when it is cooled under specified standard conditions. Contrary to straight run heavy fuels (pour point typically in the +20°C range), bunker fuels from a complex refinery generally have pour points below 0°C (range –10 to –20°C). This is because bunker fuel tanks are usually not completely heated – only before the fuel transfer pump. This can lead to problems if a vessel receives high pour straight run bunker fuel. For distillate marine diesel, the cold temperature behavior is controlled in ISO 8217 by a pour point maximum. Marine diesels with a high content of heavier n-paraffins require vigilance if wide temperature changes are expected. (Wax settling can occur, even when the pour point specification is met).
Transfer may be difficult if the fuel temperature drops below 10°C. Maintaining a fuel temperature of about 10°C above the pour point is recommended for satisfactory storage and transfer.
Water Content
Water in fuel is a contaminant and does not yield any energy. The percentage of water in the fuel can be translated into a corresponding energy loss for the customer. Water is removed onboard the vessel by centrifugal purification. If after purification, the water content remains too high, water vapor lock can occur, and pumps can cut out. If water-contaminated fuel reaches the injectors, combustion can be erratic. Water in fuel that remains standing in lines for a longer period can cause corrosion.
If water content is of fresh origin increases the fuel temperature in the settling tank and allows prolonged settling with frequent draining.
Sulphur
The tested sulfur may be above 0.50% in which case the fuel does not meet the requirements of MARPOL Annex VI unless an approved equivalent alternative is used. Refer to your company’s procedures to determine if the relevant parties must be notified. Note that the official MARPOL sample as provided by the supplier is the only governing sample regarding compliance with this statutory requirement.
Flashpoint
Flash point is the temperature at which the vapours of a fuel ignite (under specified test conditions), when a test flame is applied. The flash point for all fuels to be used in bulk onboard vessels is set at Pensky–Martens closed cup 60°C minimum (SOLAS agreement). DMX, a special low cloud point gasoil, may only be stored onboard in drums because of its < 60°C flash point.
Flash point may be below the 60°C minimum required by the SOLAS convention. Chapter II-2, reg. 4 of SOLAS states that no fuel with a flashpoint of less than 60°C shall be used. Hence the fuel is in violation of this safety standard. As a safety precaution, it is advisable to avoid hot work and smoking or any other heat source in the vicinity of fuel oil storage tanks and vents until the current flash point has been determined by the testing of tank samples. You should refer to your company’s safety and quality procedures to determine if the supplier and/or classification society should be notified.
Total Sediment Potential (TSP)
Elevated levels of TSP increases the risk of sludge formation. If elevated level is detected do not mix with another fuel and avoid prolonged storage at high temperatures. Monitor separator operation closely and if sludge is excessive, decrease the interval between sludge discharges.
Storing fuel at higher temperatures can significantly shorten its shelf life and render it unusable. Prior to consuming the fuel, ensure that the entirety of the fuel within the tank is uniformly heated to the recommended transfer temperature.
Total Sediment – Aged
Inorganic material naturally occurring in crude oil is removed in the refineries prior to the atmospheric distillation. Some minor contamination (for example, iron oxides) of a finished heavy fuel cannot be excluded. The biggest risk for sediment formation in heavy fuel is due to potential coagulation of organic material inherent to the fuel itself. Visbroken asphaltenes, if insufficiently stable, can form sediment (coagulation is influenced by time and temperature).
A decrease in aromaticity of the fuel matrix by blending with paraffinic cutterstocks can also deteriorate the stability of the asphaltenes. In cases of heavy fuel instability, only a relatively small fraction of the asphaltenes form sediment, but this organic sediment includes in its mass some of the fuel itself, and water (onboard purifying problems), and the amount of generated sludge can become quite high.
The total sediment aged is the total amount of sediment that can be formed under normal storage conditions, excluding external influences. If the total sediment aged of the heavy fuel oil markedly exceeds the specification value (0.10% m/m maximum) for all grades of IFOs and HFOs), problems with the fuel cleaning system can occur, fuel filters can get plugged and combustion can become erratic.
Total Sediment by Hot Filtration
ISO8217:2010 the total sediment by hot filtration (ISO 10307-1) shall be measured on all DMB category products that fail the visual inspection requirement to be bright and clear.
Seprarability Number
The result may suggest that the stability reserve of the fuel is high. Asphaltenes should remain within solution.
Storing fuel at higher temperatures can significantly shorten its shelf life and render it unusable. Prior to consuming the fuel, ensure that the entirety of the fuel within the tank is uniformly heated to the recommended transfer temperature.
Acid Number
All fuels have a naturally occurring acid number, however, fuels with high acid numbers arising from acidic compounds can cause accelerated damage to large diesel engines, especially the fuel injection equipment. However, fuels manufactured from naphthenic crudes can have an acid number exceeding the maximum specified in ISO 8217:2010 but still be acceptable for use. Currently no identified correlation between the acid number of a fuel oil and its corrosivity exists.
Acid number may indicate the presence of acidic compounds and, possibly, other contaminants. Depending on the origin, fuels with high acid number could cause accelerated damage to the fuel injection equipment. It is recommended to notify suppliers of this finding and ask for assurance that this fuel is safe to use. Further analyses by GCMS would be required to confirm possible presence of organic acids and other contaminants.
GC/MS Headspace Screening
GC/MS screen test may detect the presence of unusual volatile organic compounds and as such may affect the performance of machinery. GCMS extended test can identify the specific organic compounds and GCMS Vacuum distillation test (or Acid Extraction) for quantification.
Some of the compounds detected may not originate from normal petroleum refining but are known to be possibly present in blend stocks. Certain compounds may previously have caused operational problems, such as sludge formation had been reported.
The methodologies for GC/MS Extended, GC/MS Vacuum Distillation, and GC/MS Acid Extraction are different, and results are not directly comparable. It is essential to closely monitor machinery performance, as certain compounds, whether individually or in combination, may impact performance if they exceed specific concentrations under certain conditions.
Suppliers should in any case be notified of potential operational concerns and referring to ISO 8217 Clause 5, which states:
“The fuel shall be free from any materials, including added substances and chemical species, at a concentration that causes the fuel to be unacceptable for use by way of:
a) jeopardizing the safety of the ship; or
b) adversely affecting the performance of the machinery; or
c) being harmful to personnel.
FTIR Analysis
FTIR screening may indicate the presence of unidentified compounds. GC-MS on Vacuum Distillate analysis would be required to possibly determine the type of compounds. It is recommended to monitor engine operations closely and to notify your supplier when operational difficulties are encountered.
Vanadium
Vanadium will contribute to the ash content and increased ash deposits on turbo charger nozzle rings is possible. Avoid high exhaust temperatures. Increase the frequency of washing/cleaning the turbochargers if any drop in speed and/or charge air pressure is observed.
Storage temperature – Storing fuel at higher temperatures can significantly shorten its shelf life and render it unusable. Prior to consuming the fuel, ensure that the entirety of the fuel within the tank is uniformly heated to the recommended transfer temperature.
Potassium
Increased deposition and corrosion of turbocharger nozzle rings and SCR (Selective Catalytic Reactor) units is possible. Monitor engine performance closely and increase the frequency of washing/cleaning the turbochargers if any drop in speed and/or charge air pressure is observed.
Sodium
The sodium may prove difficult to reduce as it does not come from sea water. Sodium will contribute to the ash content. Increased ash deposits in the exhaust gas system are possible. Increase the frequency of washing/cleaning turbo chargers if any drop in speed and/or charge air pressure is observed.
Lubricity
Lubricity is the ability to reduce friction between solid surfaces in relative motion. The fuel itself protects some moving parts of fuel pumps and injectors from wear. Higher viscosity fuels provide sufficient lubricity. To avoid excessive wear, the fuel must have some minimum level of lubricity. Lubricity enhancing compounds are naturally present in diesel fuel derived from petroleum crude by distillation. They can be altered or changed by hydrotreating, the process used to reduce sulphur and aromatic contents. However, lowering sulphur or aromatics, per se, does not necessarily lower fuel lubricity. The use of fuels with poor lubricity can increase fuel pump and injector wear. In order to avoid this, a lubricity limit of maximum 520 μm has been defined in ISO 8217:2010 for distillate marine fuels with S content less than 500 ppm. In some areas ultra-low sulphur automotive diesel is supplied as a marine distillate fuel in order to comply with regulatory sulphur requirements.
Poor lubricity may result in fuel pump seizures due to insufficient lubrication of the fuel pump components. As guidelines on fuel lubricity may vary by engine make and type, please refer to the engine manufacturers’ recommendations.
FAME
FAME may influence the cold flow properties and the affinity to water and thereby increase the risk of microbial growth. Long term storage issues and material deposition on exposed surfaces may also be affected. In order to minimize the risk, it is important that the fuel is kept free from water, that any free water is removed from the tank bottoms and that tank drains and all filters in use are checked daily. When the fuel is stored for a prolonged period, e.g. more than 4-6 months, it is recommended to frequently monitor the fuel quality in the storage tanks.
Used Lube Oil (ULO)
The use of used lubricants (predominantly used motor vehicle crankcase oils) in marine fuels first surfaced as a potential problem in the mid-1980s. Both CIMAC and ISO 8217 working groups have discussed the technical and commercial considerations at length. Calcium, zinc and phosphorous are considered “fingerprint” elements of ULOs, and limits for these elements were set in ISO 8217:2005. According to ISO 8217:2010, a fuel oil shall be considered to contain ULO when either calcium and zinc or calcium and phosphorus exceed these limits. This, however, does not necessarily imply that the fuel oil is not suitable for use. Generally, 10 mg/kg Zn corresponds to approximately 1% used oil in the fuel. This is only an approximation; the zinc dithiophosphate content of lubricants can vary considerably.
The combination of calcium, zinc and phosphorus may suggest the presence of used lubrication oil. These metals will significantly contribute to the ash content. Sodium – The sodium may prove difficult to reduce as it does not come from sea water. Sodium will contribute to the ash content.
Ash
Depending on engine type and model, this may result in increased ash deposits in the exhaust gas system. Increase the frequency of washing/cleaning the turbochargers if any drop in speed and/or charge air pressure is observed.
Sodium (Na)
Will contribute to the ash content. Increased ash deposits in the exhaust gas system are possible. Increase the frequency of washing/cleaning turbo chargers if any drop in speed and/or charge air pressure is observed.
Calculated Carbon Aromaticity Index (CCAI)
Ignition quality may be poor and can be noticed by knocking and/or noisy engine running especially at low loads. For 4-stroke engines it is recommended to avoid low load operations to ensure satisfactory ignition. If low load operation is unavoidable, it is recommended to maintain high charge air temperatures within the limits permitted.
Storage temperature: Heating may be required in cold climates. However, storing fuel at higher temperatures can significantly shorten its shelf life and render it unusable. Prior to consuming the fuel, ensure that the entirety of the fuel within the tank is uniformly heated to the recommended transfer temperature.
Cetane Index
Cetane index is only applicable for gasoil and distillate fuels. It is a measure for the ignition quality of the fuel in a diesel engine. The higher the rpm of the engine, the higher the required cetane index. The cetane index is an approximate calculated value of the cetane number, based on the density and the distillation of the fuel. The cetane index is not applicable when cetane-improving additives have been used.
Hydrogene Sulphide (H2S)
H2S is a highly toxic gas and exposure to high vapor concentrations is hazardous and can be fatal in extreme cases. It is naturally present in crude oils and can be formed during the refining processes used to produce the fuel. H2S can also evolve from the fuels in storage tanks, barges and customer tanks. Residual fuel oils can contain varying levels of H2S in the liquid phase and in some circumstances higher levels of H2S can be observed in marine distillate fuel oils. H2S can be present in both liquid and vapor phase and the partitioning between the liquid and vapor phase depends on several factors (e.g., fuel temperature, viscosity, level of agitation, etc.). ISO 8217:2010 states a liquid-phase H2S limit of 2.00 mg/kg as measured by test method IP 570 as of July 2012. This limit intends to provide an improved margin of safety. The limit alone does not constitute a safe level or eliminate the risk of very high levels of H2S vapor being evolved in enclosed spaces.
Micro Carbon Residue (MCR)
Carbon residue is determined by a laboratory test performed under specified reduced air supply. It does not represent combustion conditions in an engine. It gives an indication of the number of hydrocarbons in the fuel which have difficult combustion characteristics, but there is no conclusive correlation between carbon residue figures and actual field experience.
Aluminium & Silicon (Catfines)
The ISO 8217 prescribed test methods are ISO 10478 or IP 501 or IP 470. Only these methods and fully equivalent methods from national standardization organizations should be used. A former industry-wide maximum limit for catalyst fines in heavy fuel was defined on Al alone (30 mg/kg). The ratio between Al and Si can, however, vary considerably between different types and manufacturers of aluminium silicate catalyst. Therefore, the test measures the sum of Al+Si. In practice, the two ways of limiting the catalytic fines content in heavy fuel give the same degree of protection. Heavy cycle oil is used worldwide in complex refining as a blending component for heavy fuel. Mechanically damaged catalyst particles (aluminium silicate) cannot be removed completely in a cost-effective way and are found in blended heavy fuel. Fuel precleaning onboard ships has a removal efficiency of approximately 80% for catalytic fines. In order to avoid abrasive wear of fuel pumps, injectors and cylinder liners the maximum limit for Al+Si defined in ISO 8217:2010 is 60 mg/kg for RMG and RMK category fuels.
Al+Si should be kept to less than 50ppm (irrespective of the ISO 8217:2012 limit of 60ppm), to ensure that the centrifuges can effectively bring this value down to less than 15ppm at the entry to the engines. If bunkered oil contains more than 50ppm of catalytic fines, injected oil is still likely to have higher than the recommended levels of cat fines due to the limitations of on board fuel treatment equipment.
Samples of heavy fuel oil should also be taken before and after each separator at intervals of 4 to a maximum 6 months for comparison.
Purifiers: Where possible, run two purifiers in parallel with minimum flow and keep the HFO inlet temperature at the optimal of 98º C to ensure efficient purification. Purifier capacity should be sufficient to cope with daily fuel consumption plus 10% in order to enable some recirculation of fuel in the settling tank to occur.
Cloud Point
Cloud point result may indicate that at- or below the measured temperature, paraffin wax crystals will start to form. Formation of wax crystals will eventually lead to choked filters and subsequently failure of the engine(s) due to fuel starvation. When the temperature increases above the cloud point, the wax crystals will dissolve. For satisfactory storage, transfer and treatment the fuel temperature must be maintained well above the cloud point.
Bacteria/Yeast/Fungi
The presence of microbes may cause operational difficulties such as clogged filters and corrosion in the fuel system and tank(s). Presence of slimy sludge in drained fuel/water and on filter surfaces is indicative of microbial contamination. Presence of water is a necessity for micro-organisms to grow and accumulation of water in the tank bottoms is a prerequisite for the growth of microbes and can act as a reservoir for microbes. In order to minimize the risk, it is important that the fuel is kept free from water, that any free water is removed from the tank bottoms and that tank drains and all filters in use are checked daily.
WAT – Wax Appearance Temperature (WAT)
The test result indicates the temperature value at which wax crystals begin to form when the fuel is cooled. Temperatures below this value should be avoided as wax starts to crystallize, causing problems such as, deposits in storage tanks and heating coils which may restrict the coils from heating the fuel, lead to blockages at the filter, reduced flow to the machinery including fuel transferring difficulties.
WDT – Wax Disappearance Temperature (WDT)
The test result indicates the temperature value that the fuel will need to be heated in order to melt all wax solids if the fuel temperature has dropped below the WAT value.
Storage temperature – Storage temperature should be maintained as low as possible (max PP + 10°C). Fuel temperature should be increased to the transfer temperature just before the transfer. Due to WAT being above storage temperature and WDT being above the transfer temperature problems with wax formation can be experienced, if wax problems are experienced, the fuel temperature in storage tank that is in use should temporarily be increased to above WDT if possible. Please consider any heating restrictions, such as cargo in adjacent tanks.