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Abstract: The extinction characteristics of non-premixed dimethyl ether and ethanol flames were investigated in order to assess the effect of the molecular structure on the combustion behavior of two otherwise similar fuels. The experiments were conducted in the stagnation flow configuration by counterflowing streams of fuel diluted in nitrogen against pure oxygen. Extinction strain rates were determined at atmospheric pressure and elevated unburned mixture temperature, over a wide range of fuel to nitrogen ratios. Two recent chemical kinetic models were used to simulate the experiments. The Lennard-Jones potential parameters assigned to dimethyl ether in the transport databases of the models were evaluated, and the effect of their uncertainty on the prediction of extinction limits of non-premixed flames was assessed. Sensitivity analyses with respect to reaction rates and binary diffusion coefficients were conducted to provide insight into the controlling physico-chemical processes. Additionally, the high-temperature reaction pathways of dimethyl ether and ethanol oxidation in non-premixed flames were identified and were used to interpret the results. [ABSTRACT FROM AUTHOR]

Abstract: Laminar flame speeds and extinction strain rates of premixed methanol, ethanol, and n-butanol flames were determined experimentally in the counterflow configuration at atmospheric pressure and elevated unburned mixture temperatures. Additional measurements were conducted also to determine the laminar flame speeds of their n-alkane/air counterparts, namely methane, ethane, and n-butane in order to compare the effect of alkane and alcohol molecular structures on high-temperature flame kinetics. For both propagation and extinction experiments the flow velocities were determined using the digital particle image velocimetry method. Laminar flame speeds were derived through a non-linear extrapolation approach based on direct numerical simulations of the experiments. Two recently developed detailed kinetics models of n-butanol oxidation were used to simulate the experiments. The experimental results revealed that laminar flame speeds of ethanol/air and n-butanol/air flames are similar to those of their n-alkane/air counterparts, and that methane/air flames have consistently lower laminar flame speeds than methanol/air flames. The laminar flame speeds of methanol/air flames are considerably higher compared to both ethanol/air and n-butanol/air flames under fuel-rich conditions. Numerical simulations of n-butanol/air freely propagating flames, revealed discrepancies between the two kinetic models regarding the consumption pathways of n-butanol and its intermediates. [ABSTRACT FROM AUTHOR]

Abstract: Blends of n- and iso-alkane components are employed as surrogates for Fischer–Tropsch (F–T) and biomass-derived jet fuels. The composition of the blends has been determined based on data available for two F–T fuel samples obtained from different sources, using a systematic optimization approach. A detailed chemical kinetic mechanism for combustion of the surrogate blends has been assembled. The mechanism has been validated against fundamental experimental data. While drawing initially from other studies in the literature, the mechanism has been improved by enforcing self-consistency of the kinetic and thermodynamic data for the various surrogate-fuel components represented by the mechanism. These improvements have led to more accurate predictions of flame propagation, flame extinction, and NO x emissions. As part of the validation process, simulations were performed for a wide variety of experimental configurations, as well as for a wide range of temperatures and equivalence ratios for fuel/air mixtures. Comparison of the model predictions to the available literature data confirms the accuracy of the mechanism as well as of the approach for selecting the surrogate blends. [ABSTRACT FROM AUTHOR]