An experimental and reduced modeling study of the laminar flame speed of jet fuel surrogate components

Abstract

The laminar flame speed is an essential combustion parameter used in the validation of chemical kinetic mechanisms. In recent years, mechanisms tailored for jet fuel surrogate components have been partially validated using the laminar flame speeds of pure components, which were derived using both linear and non-linear extrapolation techniques. However, there remain significant deviations between the results from different studies that motivate further investigation. In this study, laminar, atmospheric pressure, premixed stagnation flames are investigated for the surrogate fuels n-decane, methylcyclohexane and toluene, which are representative of the alkane, cycloalkane and aromatic components of conventional aviation fuel, respectively. Numerical simulations are directly compared to velocity profile measurements to assess the predictive capabilities of the recently proposed JetSurF 2.0 chemical kinetic mechanism. Simulations of each experiment are carried out using the CHEMKIN-PRO software package together with the detailed mechanism, with accurate specification of the necessary boundary conditions from experimental measurements. Furthermore, a skeletal version of the detailed mechanism is deduced for improved computational speed using a species sensitivity reduction method, here referred to as Alternate Species Elimination (ASE). Toluene experimental data are further compared to a detailed toluene mechanism, termed the Stanford mechanism. The experimental and numerical reference flame speeds are used to infer the true laminar flame speed of the compounds following a recently proposed direct comparison technique that is similar to a non-linear extrapolation to zero flame stretch. JetSurF 2.0 and the skeletal ASE mechanisms demonstrate excellent overall agreement with experiment for n-decane and methylcyclohexane flames, for which the original model was optimized, but poor agreement for toluene, which was not an optimization target. Improved agreement for toluene is observed between the Stanford mechanism and experiment. Results confirm that the direct comparison method yields consistent laminar flame speed data irrespective of the reactivity accuracy of the chemical kinetic model employed. The laminar flame speed results from this study are essential for the further development of chemical kinetic mechanisms and contribute to the surrogate modeling of jet fuel combustion.