Residual fuels are inexpensive, incompletely distilled petroleum products that contain high levels of impurities. These include carbon residue, ash, and sediments, along with elements like sulfur, vanadium, aluminum, and silicon. When combustion is incomplete, which can be caused by improper fuel treatment, incorrect viscosity, or issues with fuel injection timing and pressure, the heavy carbon particles don't fully convert to carbon dioxide. Instead, they get deposited on hot surfaces, such as the turbocharger's nozzles and blades, where they stick and accumulate. This buildup reduces the efficiency of the turbocharger and can cause imbalanced rotation.

Minimization:

• Ensure the fuel is purified correctly to remove impurities like sediments and water.
• Follow the manufacturer's recommendations for fuel oil viscosity and temperature to ensure efficient atomization and combustion.
• Keep the fuel injection system properly maintained and timed to achieve complete combustion.
• Select fuel with properties suitable for the engine and compliant with international standards, such as ISO 8217.

Hot corrosion is a rapid degradation of metal that occurs at high temperatures. While it typically happens at temperatures of 800-900°C, the presence of specific impurities in residual fuel can lower this threshold significantly. The primary culprits are vanadium and sodium. Vanadium, often in the form of catalytic fines, and sodium, from seawater contamination, can combine. If the ratio of vanadium to sodium is roughly 3:1, they can form a low-melting-point eutectic mixture. This mixture acts as a corrosive flux, lowering the hot corrosion temperature to around 350°C, which is well within the typical exhaust gas temperature range. This accelerated corrosion can severely damage the turbocharger blades, nozzles, and shrouds.

Minimization:

• Use a well-maintained fuel purification system with both a purifier and a clarifier to remove as many catalytic fines and seawater impurities as possible.
• Allow fuel to settle in heated tanks for an extended period, and regularly drain off water and sludge from both settling and service tanks to remove heavier impurities like catalytic fines.

Erosion is the physical wear and tear of surfaces caused by the impingement of solid particles at high velocity. In a turbocharger, which rotates at very high speeds, any unburnt carbon, ash particles, catalytic fines (cat fines), or other hard sediments that are not removed during fuel treatment will be carried along with the exhaust gases. These abrasive particles strike the surfaces of the turbocharger nozzles, shrouds, and blades, causing a sandblasting-like effect that progressively wears away the material.

Minimization:

• Good combustion minimizes the formation of unburnt carbon particles.
• This is critical for removing abrasive particles like catalytic fines and ash.
• Periodically drain heavy fuel oil (HFO) tanks to remove accumulated sludge and sediments.