Key parameters used to assess marine fuel quality and their impact on engine performance, fuel efficiency and emissions control:

1. Viscosity (at 50 deg C, cSt): determines the heating required for pumping and atomization. If too high, poor atomization gives incomplete combustion, carbon deposits, smoke and higher fuel consumption; if too low, poor lubrication of the fuel pump/injector and possible leakage. Correct viscosity at the injector (about 12-14 cSt) is essential for efficient combustion.
2. Density (kg/m3): affects the energy content per volume, the purifier/separator performance (separation from water), and the mass of fuel injected. High density fuels are harder to separate and may need special handling; density affects the calorific value per unit volume and hence the fuel consumption and the injection quantity.
3. Sulphur content (%): determines the SOx emissions (Annex VI limits) and the corrosivity of the combustion products. High sulphur requires higher-BN cylinder oil to neutralise the acid (cold corrosion) and may require a scrubber or low-sulphur fuel to comply; it also affects the exhaust gas dew point and the risk of acid corrosion in the engine and boiler.
4. Flash point: a safety parameter - the minimum temperature at which the fuel gives off ignitable vapour. It governs safe storage/handling and the maximum heating temperature; a low flash point is a fire hazard and is regulated (min 60 deg C for marine fuels).
5. Pour point: the lowest temperature at which the fuel flows. It determines the storage and transfer temperature (the fuel must be kept above the pour point to avoid solidification), affecting tank heating and pumpability.
6. Ash content (%): the inorganic residue (including catalytic fines - aluminium/silicon from the refining process). High ash causes abrasive wear of the liner, rings, injectors and exhaust valves, and deposits; it requires efficient purification and may limit the engine's ability to burn the fuel.
7. Carbon residue (Conradson/MCR): indicates the tendency to form carbon deposits in the combustion chamber, on injectors and exhaust valves; high carbon residue gives deposits, poor combustion and higher maintenance.
8. Water content (%): water in the fuel reduces the calorific value, causes poor combustion, can cause injector damage, and promotes corrosion and microbial growth; it must be removed by settling and purification.
9. Calorific value (MJ/kg): the energy content; it directly determines the fuel consumption for a given power - a lower calorific value means more fuel must be burned for the same work.
10. Cetane number (for distillate) / ignition quality: affects the ignition delay; a low cetane number gives a long delay, rough combustion, higher NOx and noise; a high cetane number gives smooth, efficient combustion.
11. Sodium, vanadium, aluminium, silicon content: cause high-temperature corrosion (vanadium/sodium) and abrasive wear (aluminium/silicon) of the engine components; they must be controlled by purification and by the choice of fuel.
12. Asphaltenes: affect sludge formation and combustion; high asphaltene content can cause sludge in storage and poor combustion.

Impact summary: These parameters determine whether the fuel can be stored, transferred, purified and atomised correctly; they affect the completeness of combustion (and hence fuel efficiency and smoke/particulates), the wear and corrosion of the engine (liner, rings, injectors, valves), and the emissions (SOx, NOx, particulates, CO2). Correct fuel quality management - heating, purification, viscosity control and matching the cylinder oil BN to the sulphur - is essential for reliable, efficient and compliant operation.