1. Marine fossil fuels:

The majority of the existing and proposed marine fuels are of the same origin. The same fuel composition may be available from renewable sources (e.g. natural gas – bio gas, methane…) but here only the most common are taken into consideration.

+ How is a crude oil feld formed?

The generally accepted theory is that crude oil was formed over millions of years from the remains of plants and animals that lived in the seas. As they died, they sank to the seabed, were buried with sand and mud, and became an organic-rich layer. Steadily, these layers piled up, tens of meters thick. The sand and mud became sedimentary rock, and the organic remains became droplets of oil and gas. Oil and gas passed through the porous rock and were eventually trapped by an impervious layer of rock, collecting at the highest poin.

                         

+ Marine fuel grades:

                         

There are at least four main grades of liquid marine fuels including marine gas oil (MGO), marine diesel oil (MDO or DO), marine fuel oil (MFO or FO) and heavy fuel oil (HFO).

• MGO is marine gas oil – DMA and DMX grades. DMA and DMX are the highest quality distillate normally supplied for marine use. Marine gasoil (MGO/DMA/DMZ) A new blend component has appeared — light cycle (gas) oil — that contains about 60% aromatics. Due to the high aromatic nature of LC(G)O, the density of a marine gasoil blended with LC(G)O will be higher than when using gasoil from an atmospheric distillation refnery. The density will typically be close to 860 kg/m3 (at 15°C). No performance or handling differences with atmospheric gasoil are to be expected. In 2010, the fourth edition of ISO 8217 standard introduced an additional grade of marine gasoil, DMZ, which has a higher minimum viscosity than DMA but is otherwise identical in its characteristics to DMA marine gasoil.
• MDO is marine diesel oil – DMB and DMC grades. DMB is a Distillate Diesel Oil, DMC is a Blended Diesel Oil. Distillate marine diesel (MDO/DMB) Distillate marine diesel (commercial denomination) typically has a lower cetane index than marine gasoil, and has a higher density. With the production slate of a catalytic cracking refnery, distillate marine diesel can therefore contain a higher percentage of LC(G)O than marine gasoil.
• MFO is a blend of MDO and HFO.
• HFO is marine heavy fuel oil – Residual Marine (RM) grade. Historically the least expensive of in use marine fuels, heavy fuel oil is used extensively in the low-speed reciprocating engines that power many of the world’s largest commercial vessels. Though the cost of the fuel is low, the use of heavy fuel oil for marine propulsion requires a cleaning system to remove excess impurities, as well as a heating system to lower the viscosity for efficient combustion. The energy required to deliver the fuel to the engine ready for combustion is quite high. The space and weight required for the heating and treatment systems associated with HFO make using this type of fuel impractical for smaller vessels. Ever growing emissions standards are also making the primary use of HFO more expensive and less practical.

Today HFO is the most common bunker fuel as it is the least expensive fuel option.

                           

2) Other fuels:

+ Natural Gas First commonly used in marine propulsion on LNG vessels, natural gas is now becoming a more popular marine fuel, primarily due to its clean burning charac-teristics, producing signi-ficantly less carbon dioxide than other fossil fuels for the same amount of heat generated. LNG additionally produces less NOx, SOx, and particulate matter than traditional liquid fuels. Natural gas must be stored as a liquid under pressure, and then warmed to a gas before combustion, creating some challenges in storage and piping arrangements.

                    

+ Nuclear fuel for marine propulsion, perhaps the most controversial of all propulsion fuels, is typically limited to large capital military vessels. These vessels take advantage of the essentially unlimited cruising range nuclear propulsion provides, without being unduly burdened by the size and weight associated with the nuclear reactor. The high power density and high endurance capability of a nuclear propulsion system also makes it an attractive choice for icebreaking operations. However, there are certain drawbacks to nuclear propulsion that generally limit its use to military vessels. These constraints include the necessity for specialized (and expensive) manning, high initial cost, the complexities of handling and disposing of nuclear materials, and extremely stringent worldwide regulation.

        

+ Biodiesel is a clean burning alternative fuel that is gaining traction in the marine industry. As its name suggests, biodieseis a fuel similar to diesel, but contains no petroleum products. Biodiesel is created through a chemical process called trans esterification, which separates glycerin from fat (such as soybean oil). When done in the presence of alcohol, this process leaves behind methyl esters, more commonly called biodiesel. This type of fuel can be used in a typical com-pression type reciprocating engine with little or no modification. Biodiesel burns cleaner than conventional diesel distillates, in addition to being made from renewable sources – these factors make biodiesel very environmentally friendly.

                       

3) Assessing Alternative Fuels for Marine Use

When assessing fuels, it is necessary to evaluate several parameters related to the technical, economic, and environmental implications of the use of each fuel.  The considerations have been grouped into five main criteria with subcriteria.
+ Engine and fuel system cost, including:
– New vessel on‐cost
– Retrofit investments
– Increased maintenance cost
+ Projected fuel cost, including:
– Projected fuel price per megajoule (MJ)
– Availability and cost of infrastructure
– Long‐term world supply
– Fuel consumption penalty (e.g., because of lesser efficiency, boil off)
+ Emission abatement cost, including:
– PM port compliance (e.g., fuel change)
– SOx SECA (e.g., scrubber) –> See this article SOx and Marine Fuel quality
– NOx SECA (e.g., SCR, EGR)–> See this article Engines with NOx and Tier I, II, III status
– CO2 EEDI (e.g., slow steaming, heat recovery)–> See this article EEDI and CO2 emission
+ Safety‐related cost, including:
– Approvals (classification)
– Additional insurance cost
– Crew training and education
+ Indirect cost, including:
– Reduced range between bunkering
– Reduced cargo capacity
– Increased waiting time in ports
The favorable attributes and drawbacks of the alternative marine fuels with regard to their practicality and affordability for marine use to be considered.