A six-component surrogate for emulating the physical and chemical characteristics of conventional and alternative jet fuels and their blends

Abstract

Conventional and alternative jet fuels, such as petroleum-derived Jet-A, coal-derived IPK, and natural-gas-derived S-8, display significant chemical and physical fuel property differences that influence their ignition characteristics. The current work addresses the need for surrogate mixtures capable of emulating the various properties of these fuels and their select blends, which are often used within compression ignited engines for acceptable ignition behavior. A six-component surrogate palette is proposed with species that are readily available within recent kinetic mechanisms, including n-dodecane, n-decane, iso-cetane, iso-octane, decalin, and toluene. The use of these species allows for a seamless compositional transition between the neat target jet fuels and their blends. The surrogate optimizer, which includes various correlations and models to estimate properties of model mixtures, is used to determine the surrogate composition that best matches target fuel properties. For an accurate ignition quality prediction during the optimization, a non-linear Derived Cetane Number regression equation is generated from Ignition Quality Tester experiments of 76 surrogate component mixtures. The newly formulated surrogates and their blends successfully capture the wide range of properties present within the target fuels, including temperature-dependent physical properties such as density, viscosity, specific heat, and volatility, along with experimental ignition delays obtained from a constant volume spray chamber. Kinetic modeling with a detailed mechanism showed that predicted ignition delay times are in good agreement with shock tube and rapid compression machine ignition delay experiments. A sensitivity analysis with variations in the composition of the Jet-A surrogate showed that its calculated ignition delay times are most sensitive to the composition of n-dodecane among the four Jet-A surrogate constituents over the range of temperatures and pressures examined. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.