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Marine BioDiesel Technical Report - opens in new window

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Biodiesel is a clean-burning diesel fuel produced from soybean and other vegetable oils instead of petroleum. Biodiesel can be blended at any level with petroleum diesel to create a biodiesel blend.  Biodiesel use in compression ignition (diesel) engines enhances engine combustion performance, improves engine lubrication and reduces air and water pollution caused by the exhaust.

Biodiesel is made from Vegetable Oils through a chemical process called Transesterification

Biodiesel is produced from vegetable oils by converting the triglyceride oils to methyl (or ethyl) esters via a process known as transesterification. The transesterification process reacts alcohol with the oil to release three "ester chains" from the glycerin backbone of each triglyceride. The reaction requires heat and a strong base catalyst (e.g., hydroxide or lye), to achieve complete conversion of the vegetable oil into the separated esters and glycerin. The glycerin can be further purified for sale to the pharmaceutical and cosmetic industries. The mono-alkyl esters become the Biodiesel, with one-eighth the viscosity of the original vegetable oil. Each ester chain, usually 18 carbons in length for soy esters, retains two oxygen atoms forming the "ester" and giving the product its unique combustion qualities as an oxygenated vegetable based fuel. Biodiesel is nearly 10% oxygen by weight.

Petroleum diesel, in contrast, is made up of hundreds of different hydrocarbon chains (roughly in the range of 14-18 carbons in length), with residues of sulfur and crude oil remaining. Diesel fuel sold today, even "low sulfur, low aromatic" diesel, contains 20-24% aromatics (benzene, toluene, xylenes, etc.) that are toxic, volatile compounds responsible for the fire/health hazards and pollution associated with petroleum diesel.

Biodiesel meeting the industry standard ASTM-D6751, in its neat (pure) form, is referred to as B-100.  When blended with petroleum diesel the resulting mixture is identified by the percentage of biodiesel in the mix; e.g. 20 percent biodiesel blended with 80 percent petroleum diesel is referred to as B-20.

ENGINE PERFORMANCE

Biodiesel methyl esters improve the lubrication properties ("lubricity") of the diesel fuel blend. Long term engine wear studies have been conducted in Europe and in the US. Porsche (Germany) determined that neat (100%) Biodiesel reduced long term engine wear in test diesel engines to less than half of what was observed in engines running on current low sulfur diesel fuel. Lubricity properties of fuel are important for reducing friction wear in engine components normally lubricated by the fuel rather than crankcase oil.

Biodiesel has been studied extensively in Europe and the U.S. for its effect on long term engine wear, particularly with respect to those components normally lubricated by the fuel itself. Fuel pumps and injector pumps depend on the operating fuel for lubrication of moving parts and shaft bearings. Initial work on the lubricity of Biodiesel, performed by Mark-IV Group and the Southwest Research Institute in 1994, established a clear advantage to blending Biodiesel with petrodiesel to achieve superior lubrication.

Tests run by Exxon showed that, compared to reference diesel fuel in 1993, a 20% blend of Biodiesel had significant, quantifiable improvements in reducing wear (193 micron scar for B-20 vs. 492 micron scar for petrodiesel) and friction (0.13 micron scar for B-20 vs. 0.24 micron for petrodiesel) while improving film coating ability of the blend (93% film with the B-20 vs. 32% film with the petrodiesel). The B-20 blend compared favorably for lubricity results against Exxon's own lubricity additive.

Heat of Combustion Properties

Relative to petroleum diesel no. 2, Biodiesel has a slightly lower heat of combustion on account of its oxygen content (petroleum diesel hydrocarbons are not oxygenated). The heat of combustion for soy methyl esters is 128,000 BTU (British Thermal Units) per gallon vs. 130,500 BTU/gal. for petrodiesel.  However, with the added oxygen, the net combustion efficiency for the blended fuel is increased, which should compensate for the slight drop in BTU content. The differences would be most noticed at low rpm and high engine load when the engine would most benefit from more oxygen.

Power Differences

Studies conducted in the U.S. and Europe generally indicate that blends of Biodiesel and petrodiesel result in small decreases in overall power output of engines.  In a Volvo marine diesel engine study in Tennessee (110-HP, 2.39 L, 4-cylinder, direct injection engine), a tractor dynamometer was used to measure power outputs under selected loads through an engine-mounted reverse drive gear. Exhaust emissions were also tested along with fuel consumption tests under various loads. The conclusions of these tests were that power produced from 100% soy methyl ester Biodiesel was from 2 to 7 percent less than produced from petrodiesel, depending on the load-speed point. However, at or near maximum throttle (3,800 rpm), the two fuels performed the same. Interestingly, at the lowest engine speed (1855 rpm) at full throttle under heavier load, there was a 13% increase in power with Biodiesel as compared to petrodiesel.

Fuel Consumption Differences

Biodiesel is a mono-alkyl esters containing approximately 10% oxygen by weight. The oxygen improves the efficiency of combustion, but it takes up space in the blend and therefore slightly increases the apparent fuel consumption rate observed while operating an engine with Biodiesel.

Engine Seals, Gaskets and Hoses

The oxygenated methyl esters of vegetable oil cause Biodiesel to have surprisingly strong solvent properties with respect to natural rubber and several soft plastics. As a result, old rubber fuel lines and some seals or gaskets on fuel tanks may slowly deteriorate in the presence of higher concentrations of Biodiesel. Fortunately, few of these solvent effects are noticed at a B-20 blend. When fuel lines or gaskets are affected, they usually get sticky over time and soften or swell, causing fuel to drip from connections. The best solution is to replace affected lines and gaskets with modern synthetic hoses and seals.

Conventional US Coast Guard approved fuel lines are resistant to Biodiesel (neat) and proven in sailboat testing over the past 3 years. In California, an approved fuel hose readily available in marine stores is:

Studies conducted for the National Biodiesel Board on the materials compatibility of Biodiesel concluded that the only hose and gasket material that was truly resistant to the solvent effects of methyl esters was Viton.

The solvent properties of the esters in Biodiesel can loosen old paint on engines or on painted surfaces in the bilge. Besides staining raw wood surfaces, Biodiesel is particularly harmful to teak decks with polysulfide seams (use extra caution when filling tanks via deck ports). Biodiesel could also harm rubber engine mounts if it were spilled and not cleaned up immediately. Use paper towels or absorbant pads to remove spilled Biodiesel and then clean the surfaces thoroughly with warm soapy water.

Warranties and Engine Manufacturer Endorsements

Marine diesel engine manufacturers in United States, Europe and Japan have all recognized the growing role of Biodiesel as a viable fuel additive, and in most cases, as a complete alternative fuel (100%). Two of the sponsors of the SUNRIDER expedition of 1992-1994 were the marine diesel engine manufacturers: Mercruiser (inboard/outboard diesel engine) and Yanmar (outboard diesel engines), endorsing Biodiesel as a suitable alternative fuel to power Bryan Peterson's 28-ft inflatable Zodiac boat around the world. This 35,000 mile adventure remains the most famous and most publicized demonstration of Biodiesel use in marine engines.

Manufacturers warrant their products against defects in materials and workmanship.  In general use of a particular fuel should have no effect on the materials and workmanship warranty.  Use of biodiesel does not "void the warranty"; this is prohibited by the Magnuson-Moss Warranty Act.  As with petroleum diesel, verify that your fuel supplier warrants the quality of their fuel.  In the U.S., diesel engine manufacturers generally endorse Biodiesel fuel meeting the ASTM-D6751 standard when used in a blend with petroleum diesel.  Caterpillar endorses the use of B-100 in many of its engine models.  Contact your engine manufacturer for updates on their acceptance of Biodiesel and Biodiesel blends as an acceptable fuel for use with their particular engine.

SAFETY AND AESTHETIC ADVANTAGES OF BIODIESEL

Boaters can appreciate the user friendliness of handling Biodiesel in their boats. The product has no noxious odors and is considered as harmless to handle as salad oil.  The product smells and feels like cooking oil.

No Noxious or Carcinogenic Fumes

Biodiesel vegetable oil methyl esters contain no volatile organic compounds that would give rise to any poisonous or noxious fumes. Biodiesel does not contain any aromatic hydrocarbons (benzene, toluene, xylene) or chlorinated hydrocarbons. There is no lead or sulfur to react and release harmful or corrosive gases. However, in blends with petrodiesel there will continue to be significant fumes released by the benzene and other aromatics present in the petroleum fraction (80%) of the blend.

No Risk of Explosion from Vapors

Since Biodiesel has no volatile components (vapor pressure of less than 1 mm Hg) and a high flash point (typically over 260 Deg. F), the product poses no risk of explosion caused by fumes accumulated below deck. The only significant fire risk would be from the spontaneous combustion of rags and paper towels soaked in Biodiesel and stored in an area with low ventilation, or high temperatures (like the inside of an engine room).
 
 
LOWER IMPACT ON MARINE ENVIRONMENT

Water pollution is reduced by using Biodiesel in boat engines since there will be more efficient burning of the fuel mixture, less carbon (soot) accumulation and particulate (smoke) emissions. Faster starting and smoother operation also should reduce the discharge of unburned fuel. Any accidental discharges of small amounts of Biodiesel should have relatively little impact on the environment compared to petroleum diesel, which contains more toxic and more water-soluble aromatics. Nonetheless, the methyl esters could still cause harm.

Comparatively Low Toxicity to Marine Plants and Animals

From 1994 through 1996, CytoCulture conducted a series of tests in collaboration with the California Department of Fish & Game (Office of Oil Spill Prevention & Response) to document the impact of vegetable methyl esters on various native species of marsh plants and marine organisms. Because larval forms of fish and shell fish are much more sensitive than the adult forms, all of the marine toxicity studies were performed with larvae of established test species. The studies indicated that the Biodiesel, while not completely harmless to the larvae of crustacea and fish, is much less toxic than petroleum fuels and crude oil.

In research conducted for CytoCulture in 1994, the LC50 (concentration required to kill 50% of the population) for larval test fish (Menidia Beryllina) exposed to soy methyl ester Biodiesel was 578 ppm relative to an LC50 of 27 ppm for reference fuel oil. In larval shrimp (Mysidopsis Bahia) toxicity assays, the LC50 for the soy methyl ester Biodiesel was 122 ppm compared to the LC50 of 2.9 ppm for the reference fuel oil.

Low Solubility and High Biodegradation Rate for Biodiesel in Water

Biodiesel methyl esters are actually quite insoluble in fresh or sea water, with a saturation concentration of 7 ppm (sea) and 14 ppm (fresh) at 17 Deg. C, whereas petroleum diesel can partition aromatics into water in concentrations of hundreds of ppm. The dissolved phase of the Biodiesel methyl esters was shown to breakdown by the biodegradation action of naturally occurring bacteria present in sea water. The half-life for the biodegradation of the vegetable methyl esters in agitated sea water was less than 4 days at 17 Deg. C., about twice as fast as petroleum diesel (reported by others).

Biodegradability of Biodiesel in the Aquatic Environment

A study conducted at the University of Idaho in 1995 determined that rapeseed Biodiesel would biodegrade about twice as fast as petroleum diesel using a standard EPA test protocol based on carbon dioxide evolution and gas chromatography. Further, the Biodiesel was shown to enhance the biodegradation rate for diesel fuel in a blend.

The biodegradation rate of rapeseed biodiesel in shake flasks with fresh water was found to be comparable to dextrose (a test sugar) and about twice as fast as for petroleum diesel. In the Idaho study (Peterson, Reece, et al., 1996), the rapeseed esters were degraded by 95% at the end of 23 days where as the diesel fuel in this test was only about 40% degraded after 23 days.

Spills of Biodiesel Can Still Harm the Environment

For the boating environment, Biodiesel should have less impact to aquatic and marine organisms than petroleum diesel if accidentally spilled or inadvertently discharged over the side. However, the US EPA still considers spills of animal fats and vegetable oils harmful to the environment. In an October, 1997 ruling under the Clean Water Act, as amended by the Oil Pollution Act of 1990, vegetable oils are considered "oil" like petroleum. (In France, Biodiesel is classified as food for transportation purposes.)

Spilling Biodiesel into the water would be as illegal as discharging petroleum fuels overboard. Waterfowl and other birds, mammals and fish that get coated with vegetable oils could die from hypothermia or illness, or fall victim to predators. Even though the Biodiesel is relatively non-toxic and less viscous than vegetable oil, it can still have a serious impact on marine and aquatic organisms in the event of a big spill. We recommend that the Biodiesel always be handled like any other fuel to avoid contamination of our bays and waterways, and that boaters obey all laws governing the handling of engine fuels and oils.
 
STORAGE CONDITIONS FOR BIODIESEL

Biodiesel can be stored for long periods of time in closed containers with little head space. The containers should be protected from weather, direct sunlight and low temperatures. Avoid long term storage in partially filled containers, particularly in damp locations like dock boxes. Condensation in the container can contribute to the long term deterioration of the petroleum diesel or biodiesel (see below). Low temperatures can cause Biodiesel to gel, but Biodiesel will quickly liquefy again as it warms up. In cold weather (near or below freezing), additives can be used to prevent gelling (fuel additives for diesel fuel used in cold weather are available from Exxon, Hammond, and other manufacturers).

Fuel tanks should be kept as filled as possible (regardless of whether they contain Biodiesel), particularly during rainy winter months or periods of inactivity, to minimize the condensation of moisture. Condensed moisture accumulates as water in the bottom of your tank and can contribute to the corrosion of metal fuel tanks, especially with petroleum diesel that also contains sulfur. The condensed water in the fuel tank can also support the growth of bacteria and mold that use the diesel and Biodiesel hydrocarbons as a food source. These hydrocarbon-degrading bacteria and molds will grow as a film or slime in the tank and accumulate as sediment over long periods of time. These hydrocarbon-degrading microbes are frequently referred to incorrectly as "algae" in advertisements for fuel treatments, perhaps because the colonies often have a reddish orange color and tend to form mats.

Petroleum diesel and Biodiesel are both susceptible to microbe growth when water is present in the fuel.  The solvent action of the Biodiesel can also cause microbial slime to detach from the inside of the tank. The accumulation of the newly released slime and sediment can be dangerous if it clogs the fuel filters and causes the engine to suddenly stop. It is very important to monitor the filters on a diesel engine that has been switched over to Biodiesel, particularly if the tank is old and has not been cleaned.

The microbial slime and sediment problem seems to worsen for boats that are used infrequently since the inactivity allows the microbes to accumulate in stable colonies. When the boat is used again, the slime and sediment can break loose and accumulate in the fuel filters. Accumulated sediment in fuel filters can then interrupt the flow of fuel and shut down the engine. As mentioned earlier, the addition of Biodiesel to a dirty fuel tank can accelerate the release of accumulated slime. When the boat is then used after sitting idle for a long period of time, the newly suspended sediment can accumulate and potentially clog the fuel filters. Check fuel filters often and be prepared to change them after introducing Biodiesel to an older fuel tank that may have accumulated slime and sediment.
 

EMISSIONS REDUCTIONS WITH BIODIESEL

Since Biodiesel is made entirely from vegetable oil, it does not contain any sulfur, aromatic hydrocarbons, metals or crude oil residues. The absence of sulfur means a reduction in the formation of acid rain by sulfate emissions that generate sulfuric acid in our atmosphere. The reduced sulfur in the blend will also decrease the levels of corrosive sulfuric acid accumulating in the engine crankcase oil over time. The lack of toxic and carcinogenic aromatics (benzene, toluene and xylene) in Biodiesel means the fuel mixture combustion gases will have reduced impact on human health and the environment. The high cetane rating of Biodiesel (ranges from 49 to 62) is another measure of the additive's ability to improve combustion efficiency.

Smoke and Soot Reductions

Smoke (particulate material) and soot (unburned fuel and carbon residues) are of increasing concern to urban air quality problems that are causing a wide range of adverse health effects for their citizens, especially in terms of respiratory impairment and related illnesses. Boaters always complain of the smoke from their diesel engines as they motor back to port. Soot accumulation on the transoms and decks of their boats is also a problem.  The lack of heavy petroleum oil residues in the vegetable oil esters that are normally found in diesel fuel means that a boat engine operating with Biodiesel will have less smoke, and less soot produced from unburned fuel. Further, since the Biodiesel contains oxygen, there is an increased efficiency of combustion even for the petroleum fraction of the blend. The improved combustion efficiency lowers particulate material and unburned fuel emissions especially in older engines with direct fuel injection systems.

Lower Hydrocarbon Emissions

As an oxygenated vegetable hydrocarbon, Biodiesel itself burns cleanly, but it also improves the efficiency of combustion in blends with petroleum fuel. As a result of cleaner emissions, there will be reduced air and water pollution from boats operated on Biodiesel blends. At a 20% Biodiesel blend, there will be a noticeable change in the odor and smoke in the exhaust. Older engines should also emit less soot under load and less carbon black during startup.

Independent research programs in Europe and the U.S. have shown that Biodiesel in a 20 percent blend (B-20) with petroleum diesel created a significant reduction in visible smoke and odor. The studies documented the reduction in hydrocarbons, carbon monoxide and particulate matter

From field observations with boats and test cars, Biodiesel appears to be even very effective in reducing smoke. The reduction in particulate Matter (PM) when B-20 is used is due to a reduction in insolubles (particles), generally composed of carbon soot. Catalytic converters (used in trucks and cars) can further contribute to the reduction in PM when B-20 is used.

Carbon Monoxide Emissions

Carbon monoxide gas is a toxic byproduct of all hydrocarbon combustion that is also reduced by increasing the oxygen content of the fuel. More complete oxidation of the fuel results in more complete combustion to carbon dioxide rather than leading to the formation of carbon monoxide. In the 1998 report by the Southwest Research Institute on the effects of Biodiesel on truck engine exhaust emissions, the levels of carbon monoxide were shown to be reduced from 8% to 22% with a B-20 blend, depending on the type of engine.

Polyaromatic Hydrocarbon Emissions

Polyaromatic hydrocarbons (PAHs) are a class of heavy oil petroleum hydrocarbons defined by their complex ring structures and unique qualities. They consist of multiple benzene ring structures that make them insoluble, slow to burn and carcinogenic. PAHs are regulated by the EPA in engine emissions. In the 1998 SWRI report, the Cummins N-14 engine had a 12% drop in PAH emissions when operating on B-20 blend relative to petrodiesel, and a 74% drop in PAHs when the fuel was switched to neat Biodiesel. These data suggest major gains in improving the air quality around diesel engines in vehicles and boats operating on Biodiesel.

Nitrogen Oxides

The nitrogen oxides result from the oxidation of atmospheric nitrogen at the high temperatures inside the combustion chamber of the engine, rather than resulting from a contaminant present in the fuel. Although nitrogen oxides (NOx) are considered a major contributor to ozone formation, they are also a reality of operating internal combustion engines. There are consistent reports of slight increases (several percent) in NOx emissions with Biodiesel blends that are attributable, in part, to the higher oxygen content of the fuel mixture. More oxygen and better combustion of the fuel also means more formation of NOx emissions with Biodiesel blends.

In several research studies conducted since 1993 in the U.S. and Europe, EPA-regulated emissions from an unmodified engine operating on a 20% Biodiesel/80% petrodiesel blend (B-20) were shown to be lower than those for petroleum diesel, except for NOx (nitrogen oxides) emissions, which can be 2-5% above baseline emissions.

Biodiesel Helps Reduce Greenhouse Gases

Unlike other "clean fuels" such as compressed natural gas (CNG), Biodiesel and other biofuels are produced from renewable agricultural crops that assimilate carbon dioxide from the atmosphere to become plants and vegetable oil. The carbon dioxide released this year from burning vegetable oil Biodiesels, in effect, will be recaptured next year by crops growing in fields to produce more vegetable oil starting material. Supplementing our dwindling fossil fuel reserves with biomass-based fuels (Biodiesel, for petrodiesel; biomass-based alcohols or hydrogen for gasoline) helps reduce the accumulation of CO2.

Chad Freckmann
Executive Director
Blue Ridge Clean Fuels
tel: +1 434 996-4473
brcfi@earthlink.net
www.blueridgecleanfuels.org

######

Information about the physical properties relevant to Marine Fuels

 

Catalyst Fines

Cloud Point

Density

Flash Point

Ignition Quality

Pour Point, Cloud Point & CFPP

Specific Energy

Viscosity

Viscosity Conversion Table

Calorific Value - See Specific Energy

Catalyst Fines

(Ref. ISO 8217:1996 - Annex D - Informative)

Catalyst Fines are the main source of potentially abrasive material in bunker fuels.

Measurement of aluminium plus silicon, with limiting values for all fuels in the Shell Specification and ISO 8217 : 1996 Fuel Tables, is intended to limit catalyst fines contamination to a level that will ensure minimum risk of abrasive wear, providing that adequate fuel pre-treatment is carried out.

The proportions of aluminium and silicon compounds that comprise catalyst fines, varies significantly from refinery to refinery, and the combined aluminium and silicon limit value of 80 mg/kg is intended to ensure that catalyst contamination will be no higher on average than has previously been implied by the limit of 30 mg/kg aluminium, that has been used in the Shell Marine Fuel Specifications for over 10 years. The aluminium plus silicon requirement of max. 80 mg/kg is therefore to be used in place of, not in combination with, the 30 mg/kg aluminium limit.

The lower aluminium plus silicon control applied to grade ISO 8217 : 1996 - Grade DMC (25 mg/kg) is based on the proportion of residual fuel that may be expected to be part of this product.

CCAI, Cetane No. and Cetane Index - See Ignition Quality

Cloud Point / Cold Filter Plugging Point (CFPP) - See Pour Point

Density

Knowledge of a fuels density is used to determine the optimum size of purifier gravity rings, to calculate a fuels calorific value, but most importantly to convert from volume to weight for invoicing purposes.

All densities listed in this publication are in terms of kg/m³ at 15°C. They should be divided by 1000 if the density in kg/l at 15°C is required.

When density is determined in accordance with ISO 3675, the hydrometer readings obtained at ambient temperature on distillate fuels, and at elevated temperatures of between 50 Deg C and 60 Deg C on fuels containing residual components, has to be converted to results at 15 Deg C using Table 53B of ISO 91-1.

When density is determined in accordance with ISO 12185, an appropriate correction for glass expansion coefficient has to be applied to readings obtained by digital density analyser at any temperature other than 15 Deg C, before conversion and application of Table 53B of ISO 91-1.

Flash Point - Residual Fuel Oils

(Ref. ISO 8217:1996 - Annex E - Informative)

Flash point is a valid indicator of the fire hazard posed by residual fuel oil, but information is available which shows that it is not a reliable indicator of the flammability conditions that can exist within the head spaces of tanks containing such fuels.

This means that residual fuel oil has the potential to produce a flammable atmosphere in the tank head space, even when stored at a temperature below the measured flash point.

Consequently residual fuel oils should be considered to be potentially hazardous and capable of producing light hydrocarbons which could result in tank head space atmospheres being near to, or entering, the flammable range. Appropriate precautions are necessary therefore to ensure the safety of people and property.

Further information and advice on precautionary measures are given in ' The Flammability Hazards Associated with the Handling, Storage and Carriage of Residual Fuel Oil - published by the Oil Companies International Marine Forum (OCIMF) December 1989. Additional information can also be found in 'International Safety Guide for Oil Tankers and Terminals (ISGOTT)', published by the International Chamber of Shipping.

Ignition Quality

(Ref. ISO 8217:1996 - Annex B - Informative)

Ignition quality of marine diesel fuels is a major factor which effects engine operation, particularly high speed units.

The Cetane Number or Cetane Index of distillate fuel indicates performance relative to a reference fuel.

The ignition quality of residual fuels is more difficult to predict because they consist of blends of many different components. However, residual fuel ignition quality may be ranked by determination of Calculated Carbon Aromaticity Index (CCAI) from density and viscosity measurements. A formula for CCAI determination is given below.

Ignition performance requirements of residual fuels in marine diesel engines are primarily determined by engine type and, more significantly, by engine operating conditions. Fuel factors influence ignition characteristics to a much lesser extent. For this reason no general limits for ignition quality can be applied, since a value which may be problematical to one engine under adverse conditions may perform quite satisfactorily in many other instances. If required, further guidance on acceptable ignition quality values should be obtained from the engine manufacturer.

Calculated Carbon Dromaticity Index (CCAI)

The viscosity and density of a fuel oil can be used to calculate its Calculated Carbon Aromaticity Index (CCAI) value, which allows ranking of its ignition performance. CCAI is calculated by using the following formula:

CCAI = D-81-141 Log10Log10 (Vk + 0.85) - 483 Log10 ((T + 273)/323)

where

Vk = Kinematic Viscosity (mm²/s) at temperature T °C:

D = Density kg/m³ at 15 °C

Pour Point, Cloud Point & Cold Filter Plugging Point (CFPP)

These characterisitics are used to assess the performance of a fuel in cold operating conditions, and to determine the temperature at which fuel filters may begin to become blocked.

Shell Marine Fuels are manufactured so that they will be suitable for the environment in which they will be used, and their characterisitics may vary slightly at different locations to ensure that they are suitable for different climatic conditions.

For this reason, the specifications for MFO up to 80 cSt at 50°C give two maximum levels for Pour Point, and the specifications for GO and MDF give two maximum levels for Cloud Point or Cold Filter Plugging Point (CFPP) as appropriate.

Pour Point, Cloud Point & Cold Filter Plugging Point (CFPP) are controlled according to the International Load Line Zone in which any particular port is located. This is done on the basis that load line zones have a reasonable relationship to ambient temperature conditions. The acceptability of the higher levels in deliveries at ports in summer and tropical load line zones should be assessed if vessels are proceeding to colder zones, particularly during winter months.

Specific Energy / Calorific Value

(Ref. ISO 8217:1996 - Annex A - Informative)

Heat of combustion, specific energy or calorific value, is a measure of the energy content of the fuel. It decreases as density, sulphur, water and ash content increase.

Specific Energy is not controlled in the manufacture of fuel except in a secondary manner by the specification of other properties.

Specific energy can be calculated with a degree of accuracy acceptable for normal purposes from the equations given below :-

Specific Energy (Gross) MJ/kg

Qg = (52.190 - 8.802 p2 10-6) [1 - 0.01 (x+y+s)] + 9.420 (0.01s)

Specific Energy (Net) MJ/kg

Qn = (46.704 - 8.802p210-6 + 3.167p10-3) [1-0.01(x+y+s)] + 0.01 (9.420s - 2.449x)

p = the density at 15 °C, kg/m³

x = the water content, % (m/m)

y = the ash content, % (m/m)

s = the sulphur content, % m/m

Viscosity

Viscosity is an important fuel characteristic, and although in itself is not an indication of quality, knowledge of a fuels viscosity is essential to enable the ship operator to determine both the temperature to which the fuel should be heated in storage to remain pumpable, and the temperature required at injection to ensure efficient atomisation.

For sales purposes the kinematic viscosity of distillate fuels is quoted in centistokes (cSt) at 40 Deg C, and the kinematic viscosity of residual fuels is quoted in centistokes (cSt) at 50°C.

The actual viscosity measurement is more usually carried out at higher temperatures, e.g. 80°C or 100°C, particularly with the more viscous and/or higher pour point fuels. The equivalent viscosity at 50°C is then calculated using the Shell conversion method. This gives results that are the same as those given by the viscosity / temperature chart in the "Shell Book of Useful Tables", and Annex C of the ISO 8217 : 1996 Specification.

In the event of any query or complaint, viscosity measurements are carried out at the original control measurement temperature with any subsequent conversion to an equivalent at 50°C calculated using the method described above.

In many new fuel specifications tables, viscosity is being quoted with reference to the unit mm2/sec, but in practice, reference is constantly made to centistokes. 1 mm²/sec is equivalent to 1 cSt.

Viscosity Conversion Table

(Ref. ISO 8217:1996 - Annex C - Informative)

The ISO 8217 : 1996 Standard specifies limiting values of kinematic viscosity at 100 °C for the fuel categories contained in the Residual Fuel Table, but as described above, in some cases kinematic viscosity is measured or quoted at other temperatures.

The table below gives approximate relationships of fuel viscosity at different temperatures.

The data should be used with caution :-

Firstly since measurements at temperatures other than 100 °C may have precision that is different

Secondly because of variations in the 'viscosity - temperature' relationships due to the variability of residual fuel composition.

Viscosities estimated from those measured at 100 °C

Kinematic Viscosity, mm²/s (1)

Measured at 100°C Approximate Estimations :-

  40 °C 50 °C 80 °C 130 °C

10.0 80 50 17 5.5

15.0 170 100 28 7.5

25.0 425 225 50 11

35.0 780 390 75 14.5

45.0 1240 585 105 17.5

55.0 1790 810 130 20.5

(1) 1 mm²/sec = 1 cSt

International Standard ISO 8217: 1996 / British Standard BS MA 100: 1996 - Residual Fuels

MDO ISO 8217

COMMERCIAL MARINE GAS OIL, DIESEL FUEL #2 (DF2),Plaza Marine bunker marine terminal fuel services INTERMEDIATE FUEL OIL 180 &Plaza Marine bunker marine terminal fuel services INTERMEDIATE FUEL OIL 380

A brief description of the ISO 8217 specification

The ISO 8217 specification is prepared in co-operation with the marine and petroleum industries to meet the requirements for marine fuels supplied on a worldwide basis for consumption on board ships.

ISO 8217 recognizes that crude oil supplies, refining methods, ships' machinery and local conditions vary considerably, which factors have led historically to a large number of categories of residual fuels being available internationally, even though locally or nationally there may be relatively few categories.

Several of the residual fuels are unique in origin to one country or area, but are nevertheless included in the ISO Specification because of their importance in the international marine fuel market.

The original ISO 8217 specification was issued in 1987.

ISO 8217 : 1996 is the second issue of this standard, it supersedes the 1987 specification which is now obsolete, and reflects several important changes in methodology. The number of fuel categories remains the same, the one deletion being counterbalanced by one addition.

Because the principal aim of this report is to examine and review fuel oils for ships, it is appropriate to define what is understood by fuel oil and gas oil in the light of the EU Directive. The Directive uses the following definitions:

1. Fuel Oil

Any petroleum-based liquid fuel falling under CN codes 2710 00 71 to 2710 00 78 (these are the numbers in the Common Customs Tariff) or which (except for gas oil as defined in 2. below), by reason of its distillation limits, falls within the category of heavy oils intended for use as fuel and of which less than 65% by volume (including losses) distils at 2500C according to the ASTM D86 method. If the distillation cannot be determined by means of the ASTM D86 method, the oil product is classified as fuel oil.

2. Gas Oil

Any petroleum-based liquid fuel falling under CN code 2710 00 69 or which, by reason of its distillation limits, falls within the category of middle distillates intended for use as fuel and of which at least 85% by volume (including losses) distils at 3500C according to the ASTM D86 method. Diesel oil as defined in Article 2 (2) of European Parliament and Council Directive on the quality of petrol and diesel oil is not covered by this definition.

Definitions of fuel oils within the shipping industry

Over the years many different definitions of fuel oil have been used in the shipping industry, and even today there is a number of different standards according to which ship owners order fuel.

Some years ago, fuel was ordered by defining it as:

gas oil,

diesel oil,

light fuel oil, and

heavy fuel oil,

stating the desired viscosity in sec. Redwood I at 1000F and the approximate specific density at 150C.

But in consequence of the technical development at the oil refineries, where cracking methods for the crude oil were improved and more products could be extracted, and in line with the enhanced environmental awareness on land – but not on board ships – this development also caused the quality of fuel for ships to deteriorate, because no environmental demands were made on the shipping industry in those days. Engine designers therefore had to start thinking in other terms and designing engines capable of using the poorer fuel oils – a development which is still in progress. At the same time, ship owners were forced to make more stringent demands as to the bunker oil they ordered, and in 1982 the first standard (which also comprised the so-called heavy oils) was introduced. It was designated BS MA 100, and it subdivides fuel oils into twelve groups, each group containing threshold values for the properties of the oil.

The main groupings in BS (British Standard) MA 100 are:

M1: Marine gas oil

M2: Marine diesel oil

M3: Distillate mixed with some residual oil

M4 – M9: Heavy oils with increasing viscosity and an upper specific density limit

M10–M12: Corresponding to M7 - M9, but without specific density limit

It is important to note that the groups refer to the viscosity of the oil. It should also be noted that this standard has several limitations. Thus, it provides no information regarding important heavy-oil properties such as:

mixability

ignition characteristics

contents of solid particles or contaminants

This BS MA 100 standard is still used by many ship owners when they order bunkers around the world, but it is probably losing popularity in favor of the ISO 8217 standard, which is likely to be the predominant standard today. ’s fuel oil recommendations are also used quite a lot. ISO 8217 and CIMAC’s definitions are often seen integrated into the same table or standard. (CIMAC means CONSEIL INTERNATIONAL DES MACHINES A COMBUSTION and safeguards the interests of engine manufacturers and users).

The classification of fuel oils according to ISO 8217 and CIMAC standards is listed in the following table:

a) Distillate grades

ISO 8217:

CIMAC:

DMX

DX

A fuel suitable for use when the ambient temperature is as low as 150C. - without preheating the oil. In the merchant marine its use is limited to lifeboat motors and emergency generators because of the oil’s reduced flash point.

ISO 8217:

CIMAC:

DMA

DA

A distillate of high quality, generally referred to as MGO (Marine Gas Oil).

ISO 8217:

CIMAC:

DMB

DB

An ordinary fuel that may contain traces of residual oil; intended for use in diesel engines which are not designed for combustion of residual oil. Generally referred to as MDO (Marine Diesel Oil).

ISO 8217:

CIMAC:

DMC

DC

A fuel that may contain substantial traces of residual oil. Therefore, this oil is not suitable for machinery and oil treatment plants that are not designed for residual fuel.

As is evident from the above table of distillate grades, ISO 8217 and CIMAC describe four categories of distillate fuel. Furthermore, the standard indicates the minimum and maximum values for the following:

Characteristic

Limit

Density at 150C kg/m3

max.

Viscosity at 400C, mm2/s

min.

max.

Flash point, deg.C

min.

Pour point (upper), deg.C

- winter quality

- summer quality

max.

max.

Cloud point, deg.C

max.

Sulphur, % (mm/mm)

max.

Cetane number

min.

Carbon residue (micro method), 10% res. % m/m

Carbon residue (micro method), % (mm/mm)

max.

max.

Ash, % (m/m)

max.

Sediment, % (m/m)

max

Total existent sediment, % (m/m)

max.

Water, % (v/v)

max.

Vanadium, mg/kg

max.

Aluminium plus silicon, mg/kg

max.

b) Residual Grades

ISO 8217:

CIMAC:

RMA 10

A 10

Please refer to the below remarks under A10 og B10

ISO 8217:

CIMAC:

RMB 10

B 10

Please refer to the below remarks under A10 og B10

ISO 8217:

CIMAC:

RMC 10

C 10

Please refer to the below remarks under C10 and up to H55

ISO 8217:

CIMAC:

RMD 15

D 15

Please refer to the below remarks under C10 and up to H55

ISO 8217:

CIMAC:

RME 25

E 25

Please refer to the below remarks under C10 and up to H55

ISO 8217:

CIMAC:

RMF 25

F 25

Please refer to the below remarks under C10 and up to H55

ISO 8217:

CIMAC:

RMG 35

G 35

Please refer to the below remarks under C10 and up to H55

ISO 8217:

CIMAC:

RMH 35

H 35

Please refer to the below remarks under C10 and up to H55

ISO 8217:

CIMAC:

RMK 35

K 35

Please refer to the below remarks under K 35

ISO 8217:

CIMAC:

RMH 45

H 45

Please refer to the below remarks under C10 and up to H55

ISO 8217:

CIMAC:

RMK 45

K 45

Please refer to the below remarks under K 45

ISO 8217:

CIMAC:

RMH 55

H55

Please refer to the below remarks under C10 and up to H55

ISO 8217:

CIMAC:

RMK 55

K55

Please refer to the below remarks under K 55

Remarks as to the above table regarding residual grades – referred to ISO 8217 and CIMAC.

The standards are arranged with the viscosity of the oils as starting point.

A 10 and B 10

Suitable for operations at low ambient temperatures in installations without preheating facilities in the storage tank, where a pour point lower than 24 or 300C. is necessary. Of these two grades, A 10 has the lower specific density and a minimum viscosity so as to improve the ignition properties.

C 10 and up to H 55

Fuel oils requiring on board treatment/purification in ordinary purifier/ clarifier extraction systems.

K 35, K 45 and K 55

Fuel for use in installations with separators specially designed for the treatment of fuel oils with higher specific densities.

As is evident from the tabular listing concerning residual grades, ISO 8217 and CIMAC describe thirteen categories of residual grades. Furthermore, the standard indicates the minimum and maximum values for the following:

Characteristic

Limit

Density at 150C kg/cub.m

max.

Viscosity at 1000C, mm2/s

max.

Flash point, deg.C

min.

Pour point (upper), deg.C

- winter quality

- summer quality

max.

max.

Carbon residue % (mm/mm)

max.

Ash, % (m/m)

max.

Water, % (v/v)

max.

Sulphur, % (m/m)

max.

Vanadium, mg/kg

max.

Aluminium plus silicon, mg/kg

max.

Total sediment, potential, % (m/m)

max.

I may seem sad that even the new 1996 version of the ISO 8217 standard fails to include limitations on several of the substances that are patently often present in fuel oils. Among them are:

Sodium

Iron

Phosphor

Lead

Calcium

Zinc

It is true that the standard indicates maximum values (in mg/kg) for aluminum and silicon, but it does not mention the size, hardness or specific density of the particles. This is quite an important parameter for abrasion of the fuel system and the cylinder liners.

The standard should also specify that the fuel oil must not contain chemical waste and spent lubricants. The standard should also make it clear if the oil in question could remain stable, so that the content of asphaltene would not give rise to the formation of sludge.

Nor is information included regarding a parameter as important as the CCAI value (CCAI = Calculated Carbon Aromatic Index, an indication of the oil’s combustion and ignition properties).

A more recent problem, which emerged in 1997 and remains unsolved, is the fact that analyses of bunker oils have revealed particles of propylene with lengths ranging from 30 m up to 5 mm. These foreign objects were identified in the US Gulf, the eastern coast of the USA, the Baltic states, and Russia. So it is starting to become a global problem. At the present time it is not clear how these particles of propylene have emerged or got into the oil.

It should also be noted that ISO 8217 and CIMAC describe only the technical and operational aspects of the maximum and minimum values associated with the extraneous substances. The environmental impact of these substances is not mentioned anywhere in the standards.

Newer investigations are in progress to cast light on this problem with various types of engine and at varying loads.

                                          
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