Heavy Fuel Oil has undergone significant changes in components in the last decade with more high aromatic components used. These components have a poor ignition quality (high CCAI) and cause instability and stratification and loss of homogeneity when two fuels are mixed. Typical incompatibility problems include sludge formation, and blockage of bunker and service tanks, pipe runs, filters and centrifugal separator bowls. Abrasive Alumina and Silica particles, Cat fines, are also smaller in LSHFO.

This creates a problem for a purifier to remove them effectively, as the purifier relies on gravity for separation of the fines. Consequently, some of the small fines are passing through to engines and causing damage. Sludge is a contaminant that results from the handling, mixing, blending, and pumping of heavy fuel while stored at, and after it leaves, the refinery. Storage tanks, heavy fuel pipelines, and barging can all contribute to the build-up of sludge. Water contamination can produce an emulsion during fuel handling. Transfer pumps can frequently provide the necessary energy to produce emulsified sludges during normal fuel transfers. These emulsified sludges can cause rapid fouling and shutdown of centrifugal purifiers, clogging of strainers and filters in the fuel oil system and rapid fouling if burned in the engine.

 Whilst large slow-speed engines are much more tolerant of poor ignition quality fuels, this is not the case in medium-speed engines and particularly of older designs. Among factors that affect ignition delay are:
Spray Formation
Heating and Vaporization Turbulent Mixing Chemical Induction Time
Even where fuels are compliant with ISO 8217:2010, they can undermine engine operation if they are poor in ignition and combustion quality.

 Sludge deposits in fuel tanks are caused by the presence of wax, sand, scale, asphaltenes, tars, and water in the bunkered fuel.
 Asphaltenic compounds formed in tank bottoms are carbonised on heating coils whilst a build-up of sludge causes extra energy being needed to heat through to useable fuel.

All fuel oil has sludge content, but its release can be caused by mixing incompatible fuels, heating and purification.

Fuel filter fouling, and glazing by; resins, waxes and gums in fuel pumps, viscometers and injectors, effects the atomisation, ignition quality and combustion of the fuel droplet and changes the fuel
GF-C rapidly cracks sludge and waxes, reduces the asphaltene particle size by shearing the bonds and breaking long chain hydrocarbons. These hydrocarbon elements are dispersed and brought back into solution. At the same time the surfaces in contact with the oil are cleaned by the GF-C action, thus restoring the mechanical side of the fuel Stoichiometric ratio.
Measurable improvements in settling, density, viscosity, separator and purification due to changes in the surface tension of fuel are a noticeable feature of treated The use of IP541/06 - a more accurate determination of combustion quality than the CCAI and CII index's - has also shown the effect of GF-C on fuels with; reduced ignition delay, improved start of main combustion and combustion period, and an increase in the rate of maximum heat release.
The combined effect of GF-C treatment can be seen, firstly in restoring the engine fuel delivery parameters, and secondly on combustion with reduced; NOx, SO2, CO, smoke, particulate, unburned hydrocarbon emissions, and engine component fouling. This in turn enables higher thermal efficiencies to be achieved and hence less fuel burned, and CO2 generated. The smoothness in heat release results in less engine damage and downtime, and less maintenance.