AN ASSESSMENT OF THE THERMAL AND OXIDATIVE STABILITY EXIGENCY FOR DIESEL FUELS IN PRESENT ENGINES AND THE SOLUTIONS MOST EFFICIENT FOR EACH SPECIFIC CASE

摘要

The progressive reduction of sulfur in diesel fuels, the increasing incorporation of fatty acid esters, the presence of metallic contaminants in fuels and the high temperatures of the new injection systems of the engines in European market, are factors that lead to different degradation mechanisms from those expected from a diesel fuel. This instability cause severe malfunctions in engines (blockage, corrosion, deposit formation, a poor fuel injection and a non-optimal combustion). It has been proven presence of metals contents greater than 0.1 mg/kg in European fuels sampled between 2004 and 2014; these contaminants act as initiators and catalysts for oxidation reactions of fuel. The European specification for diesel fuel EN-590 allows a FAME content of 5% since 2004 and till 7% since 2009; this environmentally friendly component incorporates olefins which are highly reactive to oxygen. Finally, the new diesel engines with fuel injection "common rail" expose to fuels at temperatures above 100°C, favoring the dissolution of metals and the accelerated degradation of the fuel. We have assessed the stability of diesel under specifically developed methods for simulating the new conditions. Several metal deactivators, in different combinations with dispersants and antioxidants, have been used for stabilize the fuel. The most effective combination depends on FAME content and it is also critical the presence of sulfur compounds, which are natural antioxidants but are also insoluble promoters. A suitable dispersant is highly effective for moderate sulfur contents (350 mg / kg); a proper metal deactivator is the most effective for low sulfur fuels (50 mg / kg). The antioxidant is critical to obtain the same effectiveness in stabilizing sulfur free fuel (<10 ppm) or with high content of fatty acid esters.