The most used fuel in international shipping today is HFO which accounts for approximately 77% of all fuel burned in marine engines today. This fuel is a residue from the refining industry, it has a very high energy density, a high carbon content and is relatively low in price. However, the recent worldwide effort on the environmental issue has pointed out the need for alternative fuels in the shipping sector.

With this purpose, all the stakeholders involved have started to look for alternative technologies (electrification, batteries, fuel cells, dual fuel engines and so on) and alternative fuels in order to decrease the environmental footprint of ships. The main alternative fuels that are currently available for marine use are primarily hydrogen, power to liquid fuels (the so-called e-fuels), various biofuels and LNG.

The most promising alternative fuels for maritime applications are summarized in the following table 2.01, in addition to their corresponding air emissions, availability and main issues related to their integration on board ships.

Table 2.01




Integrating issues

Natural gas

NOx, PM, CO2, CH4 (slip)

ashore, developing in ports

Combined with dual fuel engine, Cryogenic liquid storing or compressed.


NOx, PM, CO2

Ashore, obtained from fossil fuels or from renewables

Stored in liquid form (at ambient temperature), to be used with dual fuel engine, gas turbines or fuel cells (under development)



Sporadically ashore, obtained from fossil fuels or from renewables (electrolysis)

Difficult to be stored (low volumetric density). To be used coupled with fuel cells or internal combustion engines (under study) or gas turbines (under study).



Sporadically ashore, obtained from fossil fuels or from renewables (electrolysis)

Can be stored as liquid at moderate pressures (10-15 bar) or refrigerated at -33 °C.

To be used with internal combustion engines (under study) or with fuel cells.

On the other hand, considering that until now the most used fuels are HFO and Marine diesel oil MDO), it is to be noted that the quality of the fuel used by the main and auxiliary engines of the ships is very important for the good or bad running of the engines as will depend of it. The quality of these fuels is standardized under the standard ISO 8217.

In the fuel is necessary to have account the impurities that it contains, like sulphur that after combustion will produce the undesirable SOx that can provoke the acid rain, the solids and water. The solids and the water contents must be eliminated on aboard before burning the fuel in the engines and boilers to avoid abnormal running of the engines and damages. The fuel used on board must be bought to high reputation and reliability companies of bunker suppliers to avoid boarding fuel of low quality that provoke damage in the engines. When the ships receive the fuel, a sample of the same is taken to analysis in the case to get problems when the fuel is burned in the engines. The fuel used in the engines must compliance with the IMO standard in force about the sulphur content.

Before use the fuel storage on board, it is necessary to be treated to remove the solids and water contents in the fuel. The steps to treat the fuel are to heat to between 60-70C degrees in the settling tank with the purpose to remove some parts of water and solids in suspension from the settling tank. The purifiers removing the water and the solids content remaining clean the fuel. When the fuel is completely clean from impurities can be used in the injections and combustion systems.

Carry the fuel needed for each trip, avoiding the carrying unnecessary weight and the possible stratification of the same. Maintain the fuel storage to the minimum temperature possible inside of the tank. Avoid the contamination of the fuel in the storage tanks. Control of the good performance of the viscometer (MariEMS 2017).