Use of Measured Species Class Concentrations with Chemical Kinetic Modeling for the Prediction of Autoxidation and Deposition of Jet Fuels

Abstract

The production of detrimental carbonaceous deposits in jet aircraft fuel systems results from the involvement of trace heteroatomic species in the autoxidation chain that occurs upon fuel heating. Although it has been known for many years that these sulfur-, nitrogen-, and oxygen-containing species contribute to the tendency of a fuel to form deposits, simple correlations have been unable to predict the oxidation rates or the deposit forming tendencies over a range of fuel samples. In the present work, a chemical kinetic mechanism developed previously is refined to include the roles of key fuel species classes, such as phenols, reactive sulfur species, dissolved metals, and hydroperoxides. The concentrations of these fuel species classes in the unreacted fuel samples are measured experimentally and used as an input to the mechanism. The resulting model is used to simulate autoxidation behavior observed over a range of fuel samples. The model includes simulation of the consumption of dissolved oxygen, as well as the formation and consumption of hydroperoxide species during thermal exposure. In addition, the chemical kinetic mechanism is employed with a global deposition submechanism in computational fluid dynamics (CFD) simulations of deposit formation occurring in nearisothermal as well as non-isothermal flowing environments. Experimental measurements of oxygen consumption, hydroperoxide formation, and deposition are performed for a set of seven fuels. Comparison with experimental measurements indicates that the methodology offers the ability to predict both oxidation and deposition rates in complex flow environments, such as aircraft fuel systems, using only measured chemical species class concentrations for the fuel of interest.

Dependence of Fuel Properties During Blending of Iso-Paraffinic Kerosene and Petroleum-Derived Jet Fuel

“…The fuel blends exhibited deposition behavior between those exhibited by the neat fuels, with significant enhancement in stability for some of the blends. The reduction in deposition observed upon blending likely results from a combination of two effects: (1) dilution of the deleterious heteroatomic species in the jet fuel, [24][25]27 and (2) reduction in the rate of oxidation of the jet fuels, lowering deposition under partial oxygen consumption conditions. It should be noted that the oxidation rate of the FT fuel (as-produced) is extremely high due to the lack of natural antioxidants in the fuel (see discussions on Polar and Sulfur Speciation).…”

Investigation of surface deposition in a simulated fuel injector feed arm with sudden expansion/contraction

“…It was assumed that the concentration of dissolved oxygen in the jet fuel to be around 70 ppm, in line with [12,5,6,7,8]. …”

“…Previous works on the impact of both laminar [5,6] [7,8] and turbulent fluid flow [4,9,10] on jet fuel autoxidative deposition have been published using a simple straight cylindrical tubing of a constant diameter. However, in many current and future fuel injector deigns, the fuel passageways of the burner feed arm and the injector are far from this simple case and include geometric features such as: bends, annular regions, multiple parallel paths, features to introduce swirlers and large expansions and contractions in the flow.…”

Test methods for the determination of biodiesel stability

“…The most likely pathway of hydroperoxide decomposition is a homolytic cleavage between oxygen and the oxygen bond, in which alkoxy and hydroxy radicals are produced [31], and many secondary oxidation products of the autoxidation of fatty acid methyl ester are produced from the homolytic cleavage mechanism [32]. Formation of hydroperoxide will damage elastomeric gasket materials in the engine combustion mechanical system [33,34]. It has long been known that only a few compounds are not produced by the formation of hydroperoxides [35,36].…”