Combustion study of a surrogate jet fuel

Abstract

The oxidation of a three-component surrogate jet fuel (consisting of n-dodecane 66.2%, n-propylbenzene 15.8% and 1,3,5-trimethylcyclohexane 18.0%, in mol) was studied experimentally and numerically within a wide range of temperature, fuel equivalence ratio, and pressure. Three different experimental set-ups were exploited, here a jet stirred reactor (JSR), a shock tube, and a laminar burner referring to measured data of species profiles (φ = 2.0, T = 575–1100 K, p = 1 bar), ignition delay times (φ = 1.0, p = 16 atm, T = 700–1500 K), and burning velocities (T = 473 K, p = 1atm, φ = 0.6–2.0). Based on the experimental measurements, an updated detailed chemical-kinetic mechanism involving 401 species and 2838 reactions was developed, for a more detailed understanding of the oxidation and combustion of the surrogate fuel. In addition, quantum chemical methods have been applied for the determination of important initiation reactions by using the Gaussian and ChemRate software. In general, the predictions obtained with the mechanism developed in this work show a reasonable, often good agreement with respect to the measured mol fraction profiles (JSR), ignition delay time data (shock tube), and burning velocities data (flame). A negative temperature coefficient (NTC) behavior was observed in the JSR and shock tube experiments, due to the long-chain alkanes, here n-dodecane. The NTC effect was successfully predicted by the reaction model, with the predictions matching the measurements well. From the JSR experiments, 1-octene, 2-propenylbenzene, and propene were detected by GC and GC–MS as major intermediates within the oxidation of the surrogate. According to rate-of-production analysis performed at 675 K and 900 K, 1,3,5-trimethylcyclohexane (T135MCH) was found to be mainly consumed through H-abstraction reactions and forming C9H17 radicals, which mostly isomerize to iso-alkane radicals and further on, decompose to light hydrocarbons. According to the comparison of predicted data on ignition (shock tube) and burning velocity (flame) with experimental ones, the selected surrogate fuel is considered to be able to reproduce the combustion behavior of a typical crude-oil stemming jet fuel. The surrogate fuel mechanism as well as the experimental data will be of significant impact on the use in the further work of the combustion of a jet fuel and of other synthetic aviation fuels as well.