Fuel Characteristic Definition as per ISO 8217:2010

ISO specification 8217 stipulates acceptable characteristics of marine fuel oil products. In order to understand the relative importance of each characteristic it is important to understand the definition. The following definitions are deemed useful to users of marine fuels products.

Viscosity A measure of fluid resistance to flow. Viscosity of fuel oil decreases with increasing temperature. The viscosity of the fuel oil at the point of injection into the engine is key to performance. Viscosity is used to classify residual fuel types but is not a key indicator of fuel quality. For example, all other characteristics being equal, a fuel of 360 cSt is of no better or worse quality than a fuel of 400 cSt, it is just less viscous.

Density Mass per unit volume of a product. It is used to convert the volume delivered into the quantity purchased. Density varies with temperature and is an important parameter in the onboard purification of the marine fuel product.

Calculated Carbon Aromaticity Index (CCAI) The most widely accepted empirical formula to estimate the ignition quality of fuel oil. CCAI uses the physical properties of density (d) and viscosity (V) in the following equation: CCAI = d - 81 –141*log [log (V+0.85)]

Sulfur Sulfur is the main inorganic component of fuel. It occurs naturally in crude oils and tends to concentrate in the heavier fractions. Sulfur concentration in fuel oil strongly influences the choice of lubricant. Energy content of fuel oil diminishes with increasing sulfur.

Flash Point Flash point is the minimum temperature at which vapours released from the fuel oil will ignite when exposed to an open flame. The flash point of a blended fuel oil is the same as that of the lightest component in the fuel oil product.

Acid Generally, marine fuel products should not contain inorganic acids, however ISO 8217 allows for minimal acceptable levels.

Sediment Sediment in distillates is composed mainly of rust, general dirt & scale. Marine fuel oil sediment can be both inorganic and organic in nature.

Carbon Residue Carbon residue is a measure of the carbonaceous material left after the volatile components of a fuel have been vaporized in the absence of air. It is used to estimate the potential of a fuel to create deposits in an engine upon combustion.

Pour Point The pour point of a fluid is the lowest temperature at which it ceases to flow. In fuels, the pour point is largely determined by the petroleum wax content in the oil. Pour point determines the minimum temperature required for storage and handling onboard of fuel oil products.

Ash Ash is the carbon free (inorganic) residue remaining after completely burning the fuel in air. It occurs naturally in crude oils and tends to concentrate in the heavier fractions. Ash can contain hard and erosive particles, some of which may also be corrosive.

Vanadium Vanadium is a metal occurring naturally in some crude oils and is concentrated in residual components during refining. In high concentration, it can form high melting point, corrosive deposits. In combination with sodium, it can form lower melting point, oxygen deficient deposits.

Sodium Sodium occurs naturally in crude oils and is concentrated in residual streams during refining. It can be introduced into fuel streams as a scavenger used to control the hydrogen sulfide content of fuel oil, via salt water contamination, or through sodium ingress into a marine diesel engine due to salt water saturated air.

Cat Fines Cat fines contamination in fuel oil is caused by carryover of catalytic material used in the refining process and evidenced by the presence of Alumina and Silica. Cat fines are hard and abrasive.

Used Lubricant (or Lube) Oil Some used lube oil may contain components harmful to an engine, but all used lube oils may not necessarily be unfit for purpose. Some additives used to identify used lube oil such as calcium are naturally occurring in crude oil and hence residual fuel. Test methods are designed to eliminate false positives.

Calcium A soft grey alkaline earth metal, the fifth most abundant element in the earth’s crust. Essential for living organisms, particularly in cell physiology, and is the most common metal in many animals. Calcium occurs naturally in crude oils. It is introduced into the combustion space via cylinder lubrication oil. The alkaline Total Base Number (TBN) additives of cylinder lube oil contain calcium. Calcium is concentrated in the residual part of the refinery process as lighter products are removed.

Compatibility Compatibility of a fuel is a function of the stability of the two individually stable oils used to blend marine fuel oil when they are co-mingled. Heavy marine fuels are complex mixtures of hydrocarbons. Some very large molecules called asphaltenes are held in suspension by maltenes. Mixing fuels can adversely affect this equilibrium.

Fundamentals of Refinery Processing

The basic products from fractional distillation are:

Liquid petroleum gas (LPG) has carbon numbers of 1-5 and a boiling point up to 20 °C. Most of the LPGs are propane and butane, with carbon number 3 and 4 and boiling points -42 °C and -1 °C, respectively. Typical usage is domestic and camping gas, LPG vehicles and petrochemical feedstock.

Naphtha, or full range naphtha, is the fraction with boiling points between 30 °C and 200 °C and molecules generally having carbon numbers 5 to 12. The fraction is typically 15–30% of crude oil by weight. It is used mainly as a feedstock for other processes:

• In the refinery for producing additives for high octane gasoline

• A diluent for transporting very heavy crude

• Feedstock to the petrochemical olefins chain

• Feedstock for many other chemicals

• As a solvent in cleaning

Gasoline has carbon numbers mainly between 4 and 12 and boiling points up to 120 °C. Its main use is as fuel for internal combustion engines. Early on, this fraction could be sold directly as gasoline for cars, but today’s engines require more precisely formulated fuel, so less than 20% of gasoline at the pump is the raw gasoline fraction. Additional sources are needed to meet the demand, and additives are required to control such parameters as octane rating and volatility. Also, other sources such as bioethanol may be added, up to about 5%.

Kerosene has main carbon numbers 10 to 16 (range 6 to 16) boiling between 150 °C and 275 °C. Its main use is as aviation fuel, where the best known blend is Jet A-1. Kerosene is also used for lighting (paraffin lamps) and heating.

Diesel oil, or petrodiesel, is used for diesel engines in cars, trucks, ships, trains and utility machinery. It has a carbon number range of 8 to 21 (mainly 16-20) and is the fraction that boils between 200 °C and 350 °C.

White and black oils: The above products are often called white oils, and the fractions are generally available from the atmospheric distillation column. The remaining fraction below are the black oils, which must be further separated by vacuum distillation due to the temperature restriction of heating raw crude to no more than 370-380 °C. This allows the lighter fractions to boil off at a lower temperatures than with atmospheric distillation, avoiding overheating.

Lubricating oils, or mineral base lubricating oil (as opposed to synthetic lubricants), form the basis for lubricating waxes and polishes. These typically contain 90% raw material with carbon numbers from 20 to 50 and a fraction boiling at 300-600 °C. 10% additives are used to control lubricant properties, such as viscosity.

Fuel oils is a common term encompassing a wide range of fuels that also includes forms of kerosene and diesel, as well as the heavy fuel oil and bunker that is produced at the low end of the column before bitumen and coke residues. Fuel oil is graded on a scale of 1 to 6 where grade 1 and 2 is similar to kerosene and diesel, 3 is rarely used anymore. 4-6 are the heavy

fuels, also called Bunker A, B and C, where B and C are very high viscosity at normal ambient temperatures and requires preheating to about 100 °C and 120 °C respectively, before it flows enough to be used in an engine or burner. Fuel oil grade 4 does not require preheating and is sometimes mixed with off spec products, such as tank residue and interface liquid from multiphase pipelines or with grade 2 fuel oil to achieve low-enough viscosity at ambient temperatures. Fuel oil 6 is the lowest grade, its specification also allows 2% water and 0.5% mineral soil and is consumed almost exclusively by large ships in international waters, where pollutants such as sulfur is less regulated.

Bitumen and other residues like coke and tar has carbon numbers above 70 and boiling points above 525 °C. Low sulfur coke can be used for anodes in the metals industry (aluminum and steel) after processing (calcining). The remainder is a problem fuel, because of high sulfur content and even higher CO2 emissions than coal (typically 15% higher). Bitumen in the form of asphalt boiling above 525 °C is used for roofing and road paving. Asphalt concrete pavement material is commonly composed of 5% asphalt/bitumen and 95% stone, sand, and gravel (aggregates).