PD CEN/TR 17225 provides an overview of existing oxidation stability methods, with an emphasis on differences between the Rancimat (EN 14112/EN 15751) and PetroOxy (EN 16091) tests.
PD CEN/TR 17225 - assessment on oxidation stability determination methods for distillate fuels and blends thereof with FAME is useful for:
All fuels, whether of fossil source or biogenic origin, constantly degrade. Although the bulk composition remains widely unchanged, the presence of oxygen, higher temperature and catalytically active metals accelerate the oxidation of less stable compounds present, thus generating ageing products like acids oligomers and polymeric compounds. The complex and varying composition of fossil diesel fuels and the interactions of FAME and its inherent side-products with base diesel fuel components make it difficult to understand fuel ageing mechanisms at a molecular level. The determination of oxidation stability of fuels is therefore addressed by phenomenological techniques. Most test methods to characterize fuel oxidation stability are based on the determination of specific parameters, e.g. polymer formation, acidity increase, or oxygen consumption.
It has been established that the phenomenon of fuel ageing consists of two consecutive phases, starting with the depletion of the ageing reserve with few chemical changes to the bulk material, followed by the fuel ageing process itself during which the fuel is badly decomposed forming ageing polymers and acids (Figure 1, Table 1). Fuel oxidation takes place via a free radical chain process, initiated by the abstraction of a hydrogen atom from the fuel molecule and the addition of molecular oxygen to form hydroperoxides.
Generic oxidation stability test specified in PD CEN/TR 17225 allows you to determine the amount of insoluble or sludge after ageing and to estimate the storage stability of middle distillate fuels.
The total amount of solid sludge is a relevant parameter of the ageing state for a mineral diesel fuel. Oxidation of diesel blends with higher shares of FAME, however, generates dissolved ageing polymers to a significant extent. Soluble ageing polymers are known to be a major source for lacquering.
The determination of all ageing polymers, independent of their solubility, is a relevant criterion for the oxidation stability of diesel blends with higher shares of FAME, which can be achieved using test method specified in PD CEN/TR 17225.
CEN/TR 17225:2018