Heavy fuel oils used in diesel engines contain residues of e.g. vanadium, sodium, calcium, sulfur, nickel and aluminum. Their amount varies depending on the source of the crude oil, refining methods as well as mixing ratio and handling process. During combustion these residues become concentrated in the ash. The sodium and vanadium levels are of major concern since they cause high temperature corrosion at temperatures over 500°C. During combustion, these elements oxidize and contribute to formation of semi-liquid and low melting salts causing increased fouling and corrosion of components. Higher efficiency and therefore higher operation temperature, and also lower quality fuels for economic reasons are future targets, and these create additional material challenges under already demanding conditions. The corrosion resistance of various currently used and new alternative materials under simulated medium speed diesel engine exhaust system environments was experimentally clarified. The selected materials were exposed at 650 and 750°C under moist synthetic air with Na2CO3-V2O5-CaSO4 deposit up to 1000 h. The specimens were analyzed by means of cross-section microscopy.
Fuels used in diesel engines may contain residues of vanadium (V), sodium (Na), iron (Fe), sulfur (S), nickel (Ni) and aluminum (Al). Their amount varies depending on the source of the crude oil, refining methods as well as mixing ratio and handling process. Sodium is mostly from seawater contamination, iron from rusty storage tanks and pipes, while nickel and vanadium are present in oil soluble forms. During combustion these residues concentrate in the ash. The sodium and vanadium levels are of major concern since they cause high temperature corrosion at temperatures over 500°C. During combustion, these elements oxidize and contribute to formation of semi-liquid and low melting point salts that adhere to component surfaces causing increased material temperatures and corrosion destroying the protective oxide layer on metal surface.
