A recent study shows continuing improvement in sulfur, cetane number, and low-temperature properties of European diesel fuels, a trend at least partly due to increased use of additive packages.
Associated Octel Co. Ltd., London, analyzed 95 winter-grade fuels collected in late 1992 and early 1993 from gasoline stations near major European refineries. The purpose of the survey was to determine the quality of the fuel marketed from those refineries.
Quality was found to vary greatly from country to country and within individual countries. Use of additives is on the increase, however, resulting in a general enhancement of fuel quality.
Fig. 1 shows the sulfur contents of the fuels surveyed. Sulfur levels have declined in general, compared with previous Octel surveys (OGJ, Mar. 8, 1993, p. 54).
All but one fuel - a 0.32 wt % sulfur fuel from France - met the European specification limit of 0.3 wt %, says Octel. And some fuels, particularly in Scandinavia, were almost sulfur free.
The report concludes that much effort still is required to meet the requirement of the European Community Directive 91/C 174/09, which seeks a maximum sulfur level of 0.05 wt %. Octel notes that the low lubricity of lower-sulfur fuels has caused problems with some types of fuel pumps (OGJ, Aug. 16, 1993, p. 71).
Cetane numbers have remained high throughout Europe. In fact, more than half the samples contained a cetane-number improver (Fig. 2). In Nordic countries, however, many of the fuels with enhanced low-temperature properties had cetane numbers less than 50.
Only a few fuels had cetane numbers less than 48, and most were greater than 50 (Fig. 3). The highest was 58.2, found in a fuel from Mid-Europe (defined by Octel as Austria, the Czech Republic, Slovakia, Greece, and Switzerland).
In recent years, Octel's surveys have shown a consistent decrease in cold-filter plugging point (CFPP) values without corresponding reductions in cloud points. The introduction of wax antisettling additives, however, is claimed to achieve low CFPP at the expense of widening the differential between cloud point and CFPP.
The recent mild winters in Europe have prevented this theory from being tested fully on the road, says Octel, but have given refiners more flexibility in fuel blending. Cloud point and CFPP values for the tested diesel fuels are given in Figs. 4 and 5.
ADDITIVE EFFECTS
Octel chose several fuels from this survey which were rated "E" or worse in laboratory tests for corrosion (see National Association of Corrosion Engineers' scale in Fig. 6). The fuels were used to demonstrate some of the benefits to corrosion protection, cetane number, and foaming tendency of Octel's OMA 4000 series additives.
Additive packages were blended into each of the samples at typical concentrations. No attempt was made to optimize the performance of the additives.
ASTM procedure D665A was used to evaluate corrosion reduction (Fig. 6). Three treated fuels produced no corrosion; three others, acceptable ratings (B +).
Six of the survey samples having cetane numbers of 44.6-47.8 were treated with an OMA 4000 series additive to study cetane improvement (Fig. 7). Three were improved to greater than 50 cetane number, while the others could have been brought to that level by increasing the dosage, said Octel. These increased levels of additives would be no greater than concentrations found in many of the samples in the survey, the report said.
Another six fuels with severe foaming problems were selected for study (Fig. 8). In the simple bottle-shaking test used, the fuels had a foam life of 60-94 sec. AH six fuels responded to the additive, decreasing foam life to 5-9 sec.
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