Reaction Model Development for Synthetic Jet Fuels: Surrogate Fuels As a Flexible Tool to Predict Their Performance

Abstract

In the last years, the development of synthetic aviation jet fuels has attracted much interest, to provide alternatives to crude-oil based kerosene. Synthetic jet fuels can be produced from a variety of feedstocks and processes. To limit possible harmful effects on the environment when burning a jet fuel, discussions are attributed to the effects of the specific composition of a synthetic fuel on its performance and its emission pattern. A numerical tool, if available, would also be helpful within the specification process any aviation jet fuel must pass. The present work contributes to the studies and efforts how to design a synthetic jet fuel to match predefined properties, e.g. the energy content or a less harmful emission characteristics compared to Jet A-1. The approach of a generic fuel will be followed in order to design a synthetic jet fuel with pre-defined chemical properties: A chemical kinetic reaction mechanism will be elaborated capable predicting the fundamental combustion properties of the generic fuel for each possible mixing ratio of the components included. In this work, a generic mixture serving as an innovative synthetic jet fuel was studied, with n-dodecane, cyclohexane, and iso-octane chosen as single fuel components; no aromatics were added to reduce the concentration of soot precursors. Then, their fundamental combustion properties, i.e. laminar burning velocity and ignition delay time, were measured in a burner test rig and applying the shock tube technique, respectively. These experimental data were used for the validation of the reaction mechanisms developed for each single fuel component, which were then combined to the reaction mechanism for the generic fuel under consideration. To allow a comparison of the combustion behavior of the synthetic jet fuel directly, with the same reaction mechanism, to Jet A-1, toluene was added as a model component for aromatics. A reduced surrogate reaction model was produced, too. All the reaction mechanisms elaborated are shown to reasonably predict the fundamental combustion properties within the parameter range considered. The compact reduced surrogate model can serve as a virtual jet fuel within numerical simulations. Thus, ultimately, an estimation of the suitability of an innovative synthetic jet fuel as a blending component to crude-oil kerosene is enabled. As a result, CFD simulations can be run efficiently tackling the combustion of a synthetic fuel in a jet engine under practical conditions and by taking into account the interaction between turbulence and chemistry.

A combined experimental and modeling study of combustion properties of an isoparaffinic alcohol-to-jet fuel

“…Comparison of the flame speeds of AtJ-SPK (this work) as well as of iso-octane [48] obtained from measurements (symbols) and those obtained from predictions using the new LLNL mechanism (curves) is shown in Fig. 5.…”

“…This definition was used for ignition delay instead of maxima in maximum CH(A) concentration as it reduces the computational time, and the controlling chemistry is expected not to change with either of the choices for identifying ignition delay. experimental data of Jet A-1 [11,12] and iso-octane [48] measured at the same experimental conditions.…”

“…Figure 5 Results of the measured (symbols) laminar burning velocities for AtJ-SPK (Alcohol-to-Jet Synthetic Paraffinic Kerosene) and iso-octane [48], each in mixture with air at T = 473 K in comparison with calculated flame speeds (curves) using the new LLNL mechanism (present work).…”

Reaction Model Development of Selected Aromatics as Relevant Molecules of a Kerosene Surrogate—The Importance of m-Xylene Within the Combustion of 1,3,5-Trimethylbenzene

“…Consequently, the combustion of Jet A-1 is modeled by means of a model fuel, also known as a surrogate; see e.g. [8][9] and refs. therein.…”

Experimental Characterization of Flame Structure and Soot Volume Fraction of Premixed Kerosene Jet A-1 and Surrogate Flames

“…The mechanism developed by Wang et al [30] and Xu et al [31]: the "HyChem" (Hybrid Chemistry) mechanism for JP-8 (119 species, 841 reaction). • A mechanism developed by Kathrotia et al [32] for kerosene surrogate mixtures of N-decane, cyclohexane, isooctane and toluene. Since this mechanism does not include all species necessary for the surrogate, a mixture of 42.67 vol.-% N-decane, 33.02 vol.-% isooctane and 24.31 vol.-% toluene was calculated based on Dooley et al [33].…”