Component Interactions in Jet Fuels: Fuel System Icing Inhibitor Additive

Abstract

In view of its widespread application in aviation turbine fuel, diethyleneglycol monomethylether (DiEGME), and its interactions with water and n-heptane have been characterized using turbidity, interfacial tension, water activity and water absorption measurements. This additive has been implicated in a number of problems in recent years, which have arguably arisen from its various physico-chemical interactions with fuel and fuel system components, for which few data were hitherto available. The present study has therefore addressed the more fundamental aspects underlying such interactions using n-heptane as the hydrocarbon. Turbidity results indicate an increased level of water solubilization owing 2 to the formation of DiEGME-water clusters (~1:8 ratio) as the DiEGME concentration exceeds its specification maximum value of 0.15% (w/v) in fuel. Interestingly, this same composition is found in separated water resulting from additive partitioning from fuel leading to ~50% DiEGME/water mixtures. The combined use of interfacial tension, water activity and absorption measurements, and solubility parameters is able to explain this tendency as being due to a reduction in water activity in the presence of DiEGME, this latter property being reduced significantly above 50% DiEGME, which therefore appears to be the most thermodynamically-stable composition. Water activity considerations also provide the basis for understanding the action of DiEGME as a thermodynamic icing inhibitor, consistent with the role that hydrogen bonding plays in reducing water activity, and in line with water activity-based ice nucleation theory (Koop, T.; Luo, B.; Tsias, A.; Peter, T. Nature 2000, 406, 611-614).Correspondingly, the thermodynamic activity of DiEGME, derived herein using a Gibbs-Duhem treatment of water activity data, is shown to be reduced considerably in the presence of low levels of water (< 0.1 mole fraction), which would be sufficient to restrict the fuel solubility of this material as observed in practice.

Effects of TRiEGME on water icing behavior in aviation turbine fuel

“…This was partially attributed to the increased polarity for EGME, DiEGME, and TriEGME. The hydrogen receptor for TriEGME was four compared with two for EGME, while the calculated dipole moment of DiEGME was 1.16 D compare with 1.01 D for EGME . In practice, it was evitable to mix free water in the fuel and in order to prevent the formation of ice crystal at environmental temperature above −47 °C, it was necessary to determine the quantity of FSII required to add to the fuel to prevent free water solidification at −47 °C.…”

“…Diethylene glycol monomethyl ether (DiEGME) is currently the only approved civil aviation fuel system icing inhibitor (FSII) with minimum concentration of 0.07 vol.% and maximum 0.15 vol.% . It is a hydrophilic material with the potential for strong hydrogen bonding to water, thus increasing water solubility and lowering freezing point . It has been successfully applied to military aircrafts for years till recently, it has been identified to be associated with the peeling of fuel tank topcoat material, which results in increase in scheduled and unscheduled maintenance costs and decrease in aircraft mission capabilities .…”

Dual Action Additives for Jet A-1: Fuel Dehydrating Icing Inhibitors

“…For this reason, the water added to the fuel surrogate was in addition to the amount of water present in its dissolved form (i.e., 59 ppm). Table 1 clearly indicates that the products of FDII hydrolysis preferentially partition into water with the same order of magnitude as the DiEGME [11]. Most notably for the hydrolysis products of FDII's 5 and 8, partitioning into lower concentrations of water (i.e., 90-500 ppm v/v) is two to three orders of magnitude more favourable than suggested in the calculation (Figure 3), which assumes a 1:1 ratio of water/fuel.…”

“…Another source of free water in the fuel tanks derives from the condensation of atmospheric moisture. As the aircraft is descending from cruise altitude, air is drawn into the fuel tanks through the vent system; the moisture in the air condenses as it comes in contact with the cold fuel and tank surfaces at the end of a long flight [11].…”

“…In addition, the presence of DiEGME in the water contained within the fuel alters interfacial properties, and can impair the performance of filters. Particularly, the separation efficiency of filters/coalescers can be compromised [11]. DiEGME is also toxic at the concentrations required for effective de-icing.…”