• Viscosity: indicates the resistance to atomisation/pumping. If too high, poor atomisation -> carbon deposit, poor combustion, high fuel pressure/overloading of the injection pumps; if too low (dilution), injection timing and energy may be reduced.
• Density (measured at 15 C): high density indicates aromatic content and affects injection (centrifugal purifier) and the energy per unit volume; out-of-range density affects purifier separation and possibly injector calibration.
• Sulphur content: must meet emission regulations (0.5% or lower) and the engine/high-temperature corrosion of exhaust valves/piston ring/cylinder wear and boiler acid dew-point; excessive sulphur causes acid corrosion and acid deposits.
• Flash point: the safety parameter (min stored flash point ~60 C for low-flash fuels). Low flash point is a serious fire/explosion hazard in storage and handling.
• Pour point / cold flow properties (CFPP): affects pumping/heat tracing in cold weather; high pour point oil can solidify and block filters/pipes.
• Water content: water causes poor combustion, corrosion, and can damage the injectors and accelerate wear; excessive water can stall the purifier and cause sludge.
• Total sediment / ash content: ash (vanadium, sodium, aluminium/silicon catalytic fines, carbon) causes abrasive wear of injection equipment, turbocharger and exhaust gas system, and deposits; catalytic fines cause severe wear of the fuel pump/unit injector plungers.
• Aluminium + silicon (cat fines): abrasive solids cause rapid injection pump and injector wear.
• Carbon residue / Con-M: tendency to leave carbon deposits affecting combustion chamber cleanliness.
• Sodium/vanadium: causes hot-corrosion, slagging on valves/turbocharger and high-temperature corrosion.
• Acid number (TAN) and compatibility: acidity and asphaltene precipitation/stability which can cause sludge formation.

Impact if out of range: poor/abnormal combustion, harmful deposits, accelerated wear, fuel system blockages, emissions non-compliance, safety hazards and reduced engine life.

• High water content: run the fuel purifier(s) continuously and at the correct throughput/gravity setting, drain water from tanks/sludge, blend/transfer, and avoid suction from the tank bottom; increase centrifuge/filter maintenance.
• Excessive sulphur: where permitted, use compliant fuel (low-sulphur) in the sulphur emission control areas or maintain the scrubber/EU ECA compliance, adjust TBN (lube oil feed rate) to neutralise the acid (increase lube oil feed/cylinder lubrication), and monitor exhaust gas temperature/acid dew point protection.
• Low flash point: stop burning the suspect fuel, isolate and dispose/drain it, test and only use fuel within safe limits, and review supplier quality; increase vigilance for leakage into the fuel system.
• Acid number: treat the acid condition - increase purifier efficiency, keep the oil circulating to keep asphaltenes in suspension, and reduce retention time; add a suitable stabiliser/anti-sulphate-ash additive, and if necessary blend or replace the fuel.
• Ash / catalytic fines: increase purifier throughput efficiency, warn of upstream (sludge) and set a lower purifier rating, add a suitable dispersant, and minimise usage of the contaminated fuel; check injection pumps and filters more frequently; if very high, use a sludge-tolerant/emergency procedure and notify for a quality claim/sampling.

In each case the remedial action is backed up by: segregating/quarantining suspect tanks, keeping the fuel system (filters, purifiers) well maintained, taking proper retained samples, notifying the charterer/supplier for claim, and monitoring engine condition.