Oxidation of a Coal-to-Liquid Synthetic Jet Fuel: Experimental and Chemical Kinetic Modeling Study

Abstract

The kinetics of oxidation of a Coal-to-Liquid (CtL) Fully Synthetic Jet Fuel (FSJF) was studied using three complementary experiments operating over a wide range of conditions: a jet stirred reactor (p = 10 bar), constant mean residence time of 1 s, over the temperature range 570–1070 K, and for equivalence ratios φ = 0.5, 1.0, and 2.0; a shock-tube (p ∼ 16 bar, temperature range between 900 and 1400 K, φ = 0.5 and φ = 1), and a conical flame burner (preheat temperature T0 = 473 K, and for two pressure regimes, p = 1 bar for equivalence ratios ranging from 0.95 to 1.4, and p = 3 bar for equivalence ratios ranging from 0.95 to 1.3). Concentration profiles of reactants, stable intermediates, and final products in the jet stirred reactor were obtained by probe sampling followed by online and off-line gas chromatography analyses and online Fourier transform infrared spectrometry. Ignition delay times were determined behind reflected shock waves by measuring time-dependent CH* emission at 431 nm. Flame speeds were determined by applying the cone angle method. Comparison with corresponding results for Jet A-1 was performed showing similar combustion properties. The oxidation of the CtL-fuel under these conditions was modeled using a detailed kinetic reaction mechanism consisting of 8217 reactions and 2185 species and a 4-component surrogate fuel mixture (n-decane, iso-octane, n-propylcyclohexane, and n-propylbenzene). A reasonable representation of the kinetics of oxidation of this FSJF was obtained. The model showed good agreement with concentration profiles measured in a jet stirred reactor at 10 bar over a range of temperatures (550–1150 K) and equivalence ratios (0.5–2). Acceptable agreement between measured and predicted ignition delay times was found for the investigated fuel air mixtures, with significantly longer ignition delay times predicted. Also, the ignition behavior of the surrogate is mainly influenced by the n-alkane and not by the addition of iso-alkanes, naphthenes, and aromatics. In general, a reasonable agreement between predicted and measured burning velocity data exists, with larger deviations at higher pressure. No deviation is to be seen between burning velocity data for Jet A-1 and CtL, within the uncertainty range. Within the parameter range studied, the measured data of burning velocity and ignition delay time agree with data obtained earlier for petrol-derived kerosene. Our findings support the potential of the CtL investigated to serve as an alternative aviation fuel.