Long-Term Storage Stability of Diesel Fuels - Effect of Aging on Injector Fouling-Stabilization by Additives or Hydrotreating

Storage stability of different diesel fuels containing cat-cracked stocks was examined using various aging conditions. The degradation of fuel during storage was monitored through insoluble formation but also through reaction of nitrogen compounds known to be involved in the fuel degradation process. The influence of aging in injector fouling tendency was also investigated on an IDI engine on test bench. Various stabilizer additives (tertiary amines, dispersant…) were tested. Best results were obtained with dispersants which prevent sediment agglomeration making them able to cross the filter mesh. Additives limit indole evolution without inhibiting completely sediment formation, proving that other reactions take place. We showed that fuel oxidability is not modified by additives. None of the tested formulations is effective on fuel darkening. After aging, surfactants remain effective on injector fouling. Another way of improving the storage stability of Diesel fuel is hydrotreatment. A fuel was hydrotreated at different severity levels and the effect on stabilization was shown. It was demonstrated that hydrotreating makes it possible to achieve more complete stabilization than using additives. Particularly color stability is considerably improved after hydrotreatment. Stabilization was achieved for mild operating conditions for which hydrodenitrification is not complete, only indoles are transformed. To inhibit fuel degradation, hydrotreatment should reduce other sediment precursors than nitrogen compounds. We also demonstrated that hydrotreating renders fuels more sensitive to oxidation.