In the literature, various quick tests to predict the ageing stability of middle distillates are described.
59 gasoil components and finished products were tested, using methods recommended by a detailed literature study DGMK-Report 484, namely:
- the colorimetric/spectrophotometric method according to R. K. Solly and S. J. Marshman,
- the quantification of Soluble Macromolecular Öxidatively Reactive Species (SMORS) according to M. A. Wechter and D. R. Hardy,
- the determination of phenalene and phenalenone as well as non-basic nitrogenous aromatics.
ASTM D 4625-92 was used as a reference test (storage at 43 °C over a period of 12 weeks, with air
The results obtained showed that none of the methods mentioned above are suitable as a reliable quick test, because the regression analysis shows no acceptable correlation between the data obtained and the insolubles derived from the reference test. The hypothesis of Pedley et al., referring to the ageing mechanism of middle distillates, could not be confirmed. The spectrophotometric method gives the best result, considering the total nitrogen content. The accuracy of the prediction of ASTM-Test results is about 75%.
The additionally carried out "Rancimat-Test" does not correlate at all with the insolubles based on ASTM D 4625-92.
The insolubles as determined according to ASTM D 4625 neither do correlate with the amount of sediments which are formed after one year's storage under genuine conditions.
On the other hand, the supplementarily conducted „Shell Window Test" allows a prediction of the longterm storage behaviour with a likelihood of 78 % which is expected to improve after a revision of the method with regard to reproducible test conditions.