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The basic definition of an internal combustion engine states that it is a component that converts chemical or fuel energy into mechanical energy. This is governed by the law of conservation of energy. This definition is well established to all kind of components which converts chemical energy to mechanical energy, from huge marine engines to smaller engines of 2 wheeler. Fuel is very crucial for obtaining power so, fuel parameters need to be understood and stressed.

Fuel Parameters:

  • Fuel density: it is helpful in calculating the amount of fuel quantity in a bunkering operation.
  • Pour point: point below which fuel loses the ability to flow. It is basically a temperature point.
  • Viscosity index: it is a dimensionless quantity that gives an idea to preheat the fuel before an operation.
  • Calculate carbon aromatic index (CCAI): the CCAI number is inversely proportional to the efficient burning of fuel. The higher the value of the CCAI number more will be the delay in ignition. This is used mainly for HFO, CCAI of HFO is 870.
  • Cloud point: it is the temperature below which fuel wax formation starts in fuel. If used below this point, filters will get clogged.
  • Water content: while blending fuel or while bunkering operation water/moisture is added to fuel, which on combustion causes corrosion.
  • Cetane number: it is an indication of fuel’s property to self ignite or knocking of the engine. The higher the cetane number lower will be the knocking(the better the combustion and lower the delay). 

*Distillates: These are those fractions of crude oil which gets evaporated during distillation and later condensed to liquid fractions.

Marine Fuels:

  • Heavy fuel oil (HFO): It is well known as bunker fuel or residual fuel .it is the leftover residue in the distillation and cracking process of crude oil. After extracting the high-quality hydrocarbons from crude oil the rest over oil is HFO. It contains harmful hydrocarbons, higher sulfur concentrations, nitrogen, aromatics, etc. which on combustion are very harmful. It is used in the marine industry only due to its lower price. HFO today is generally used after blending it with cleaner distillate fuels to ensure its viscosity and flow characteristics. The blended product of HFO is known as IFO 380, IFO 180 (IFO: Intermediate fuel oil).
  • Very low sulfur fuel oil (VLSFO): Fuel oil is generally referred to as residual oil in the distillation of crude oil. VLSFO was introduced to meet the global sulfur cap constraints on sulfur emissions to 0.5% by mass. VLSFO is a blended fuel where blending is done between HFO and cleaner distillates, in which concentration of distillates is higher than HFO.
  • Marine diesel oil(MDO): MDO is considered as a middle distillate of HFO. It is also known as Intermediate fuel oil (IFO), it is a blend where the concentration of HFO is lower than distillate fuel.
  • Marine Gas Oil (MGO): MGO is from the category of ultra-low sulfur fuel oil (ULSFO). Due to the emission norms laid by countries for their coastal regions to reduce sulfur content to 0.1% and declaring such regions as emission control areas-ECAs. A compatible fuel to maintain the norms was introduced as MGO. MGO contains mostly the distillates it is much more similar to diesel but its density is higher than diesel. Unless other fuel oil, it does not require any preheating to maintain its viscosity and flow characteristics. Today MGO is having many complications while operating because it is a bit difficult to tune engines with MGO. Due to this, it is only used in ECAs.
  • LNG: Liquefied Natural Gas can be a feasible option for marine engines while complying emission norms of 0.1% sulfur emissions. Due to the increased production of LNG, it is well suited for modern-day engines. Finland’s WÄRTSILÄ and Germany’s MAN Diesel and Turbo (MAN DT) have introduced a dual-fuel engine to use LNG as fuel. As of now a small amount of oil is required as pilot fuel for the combustion of LNG. 

Microbial Infestation in Fuels:

Image for Microbial Growth

Source: Internet, Courtesy: agro.crs

Microbial growth in fuel storage is caused by bacterial and fungal growth. Virtually all types of fuels contain a certain water content which acts as a breeding ground for bacterial growth. Generally, this problem occurs in diesel and fuel oils, as gasoline contains lead and other additives it acts as a poison for bacteria. During bunkering and storage of fuel oil, there is an addition of moisture in fuel due to preferable temperature bacteria starts growing in storage tanks. This bacteria can also attack lube oil. Due to this bacterial growth property of fuel changes such as pour point, viscosity, etc. fuel loses its ability to burn effectively and microbes in fuel degrade the fuel and lead to the formation of acids and sludge, deposits, and serious corrosion. When the microbes reproduce they produce eggs, which when rot gives out the foul smell in the form of hydrogen sulfide. This smell is an indication that oil is contaminated by microbial infestation. This is the problem faced while using VLSFO due to increased microbial infestation storage tanks of VLSFO was turned into the wax and such incidents have been reported. as VLSFO & ULSFO can’t be preheated to reduce the growth of bacteria certain chemicals are added to reduce bacterial growth. Due to the high concentration of water in biodiesel, it is very difficult to store it on board.

The adoption of the anti-bacterial coating of storage tanks and using fuel additives can yield good results in controlling the microbial infestation of fuel. 

About the Author

Hello, I’m Hardik

A Marine Engineer by profession, Hardik loves to read and write about the technical happenings in the maritime industry.