Energy & Fuels 1995,9, 906-912
906
Quantitative Evaluation of Jet-Fuel Fouling and the Effect of Additives E. Grant Jones," Lori M. Balster, and Walter J. Balster Systems Research Laboratories, Inc., A Division of Space Industries International, Inc., 2800 Indian Ripple Road, Dayton, Ohio 45440-3696 Received February 13, 1995. Revised Manuscript Received May 31, 1995@
Dynamic near-isothermal techniques have proven to be valuable in assessing the tendency of aviation fuels t o form surface and bulk insolubles under conditions of thermal-oxidative stress. These methods are applied to the investigation of three representative jet fuels, POSF-2827, POSF-2980, and POSF-2934, and changes in these fuels caused by the introduction of four candidate additives. Neat and additized fuels are evaluated during flow through a tubular heat exchanger at 185 "C. The average surface-deposition rate as a function of stress duration and the quantity of both surface and bulk insolubles are determined during complete conversion of the dissolved oxygen. The additives, introduced individually, include a common antioxidant, a metal deactivator, a dispersant, and a combination detergenvdispersant. The impact of each additive is discussed. Dispersants are found to cause the greatest reduction in total quantity of bulk and surface deposits. Several criteria are considered for evaluating fuels and fueyadditive combinations.
Introduction Consideration of the thermal-oxidative stability of aviation fuels is becoming more important as fuels are subjected to increased stress at elevated temperatures. Enhanced aircraft performance creates additional heat and, in turn, stressing of the aviation fuel. Being the primary heat sink, fuels must be capable of withstanding severe oxidative stress without bringing about system fai1ures.l Unfortunately, the reaction products of autoxidation include insolubles which tend to foul heated surfaces, causing reduced efficiency and blockage in heat exchangers and other undesirable changes in nozzles and servo-controls. Such problems are exacerbated by the presence of small quantities of fuel components containing heteroatoms such as nitrogen and sulfur. In general, fuels having fewer polar components are preferable because they produce fewer insolubles,2a One approach to improving the stability of fuels is based on heteroatom removal. Clay or hydro treatment may accomplish the removal of some polar components but does not always represent a practical solution because of the cost involved. Another approach involves the introduction of low-cost additives-an approach that is particularly appealing when lesser quality or borderline fuels can be upgraded. Additives such as antioxidants for slowing oxygen consumption, metal deactivators for chelating dissolved metals or passivating tube walls, and dispersants for increasing solubility would appear to hold the most promise from the standpoint of * Author to whom correspondence should be addressed. Tel: (513) 252-4264. @Abstractpublished in Advance ACS Abstracts, July 15, 1995. (1)Edwards, T.; Anderson, S. D.; Pearce, J . A.; Harrison, W. E. High Temperature Thermally Stable J P Fuels-An Overview. AIAA Paper 92-0683, Presented at the 30th Aerospace Sciences Meeting and Exhibit, Reno, NV, 6-9 January 1992. (2) Hazlett, R.N.Thermal Oxidation Stability of Aviation Turbine Fuels, ASTM Monograph 1;American Society for Testing and Materials: Philadelphia, 1991; (a) pp 150-151; (b) Chapter E.
surface fouling. Additives for achieving other specific objectives include corrosion inhibitors, lubricity improvers, icing inhibitors, static dissipators, and pipeline-drag reducers. Their application to jet fuels has been summarized by MarteL3 As an aid in the selection of appropriate additives or additive packages, we need data from simple laboratory tests on each neat fuel and its additized analogue and, in addition, straightforward criteria for their interpretation. One of the challenges facing those studying aviation fuels is to gain a basic understanding of insoluble formation that will assist in the ranking of fuels and the prediction of their behavior at elevated temperatures. This is a formidable task, considering the diversity of fuel chemistry. Nevertheless, dynamic nearisothermal techniques, developed within our laboratory, have provided new insight into the formation of bulk and surface insolubles in the Jet-A fuel POSF-2827 under controlled chemical condition^.^-^ These methods have proven t o be valuable in assessing the tendency of fuels to form surface and bulk insolubles at selected elevated temperatures. The objective of the current study was t o apply these techniques to a limited matrix of three jet fuels and four additives. The neat and additized fuels were studied to determine (1)differences in the neat fuels, (2) beneficial or deleterious changes from additives within a single fuel, and (3) criteria for evaluating and comparing different combinations of fuels and additives. (3)Martel, C.R. Military J e t Fuels, 1944-1987, Technical Report AFWALTR-87-2062; Air Force Wright Aeronautical Laboratory: WrightPatterson Air Force Base, OH, 1987. (4) Jones, E. G.; Balster, W. J. Energy Fuels 1993, 7, 968-977. (5) Jones, E. G.; Balster, W. J. Prep.-Am. Chem. Soc., Diu. Pet. Chem. 1994,39 (l),78-81. (6) Jones, E. G.;Balster, W. J . Prepr. Pap.-Am. Chem. Soc., Diu. Fuel. Chem. 1994, 39 (31, 952-957. (7) Anderson, S. D.;Jones, E. G.;Goss, L. P.; Balster, W. J. Effect of Additives on the Formation of Insolubles in a Jet Fuel. Proceedings of the 5th International Conference on Stability and Handling ofLiquid Fuels, Rotterdam, 3-7 Oct 1994, Giles, H. N., Ed.; U. S. Department of Energy: Washington, DC, 1994; Vol. 1, pp 291-301.
0887-0624/95/2509-0906$09.00/00 1995 American Chemical Society
Jet-Fuel Fouling and the Effect of Additives
Energy & Fuels,
Vol.9,No.5, 1995 907
Table 1. Fuel Properties POSF-2827 Jet-A straight run 266 0.079 0.001 -43 19 0.001
tYPe treatment JFTOT breakpoint ("C) total sulfur (%) mercaptan sulfur (%) freezing point ( " 0 aromatics (~01%) total acid no. (mg of KOWg) iron content (ppb) copper content (ppb) inherent insolubles @g/mL)
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