A new method for determining the concentration of inorganic particles in marine residual fuel oils has been developed. This method offers direct gravimetric measurement of abrasive particles present in the fuel, and, as such, the method is independent of the chemical composition of inorganic particles, including those of cracking catalysis. The method is a more meaningful tool in assessing wear potential in a diesel engine and its fuel handling system than the older aluminum analysis method.
In the new method, a centrifuge is employed to transfer the particles from the fuel to a nonfuel phase. During the transfer, the particles pass through an aqueous phase containing oxalic acid in which water soluble salts and rust particles are removed. The particles then are collected in a nonaqueous phase, heavier than water. Subsequently, the particles are transferred to a crucible where they are dried and ashed to remove carbonaceous material. The particles then are weighed to determine the amount of inorganic particles present.
An ASTM round robin was conducted to determine the precision of the new centrifuge method. Data obtained by seven laboratories on eight fuel samples were statistically analyzed to formulate a precision statement for the new method. At 150 ppm m/m inorganic particles content, repeatability is 24 ppm m/m, and reproducibility is 68 ppm m/m. This precision appears reasonable and compares well with the precision of other related ASTM methods such as Water and Sediment in Crude Oils and Fuel Oils by Centrifuge [D 1796-68 (1977)] and Particulate Contaminant in Aviation Turbine Fuels [D 2276-73 (1978)].