Experimental study on the structure of opposed flow gaseous diffusion flames doped with n-decane

Abstract

The destruction of n-decane is investigated with a perturbative approach by adding hundreds of ppm to the fuel stream of two gaseous counterflow diffusion flames at atmospheric pressure: a blue methane flame and an incipiently sooting ethylene flame that offer distinct reacting environments. The detailed chemical structure of the flames including the products of n-decane consumption is determined using a microprobe gas sampling technique followed by GC/MS analysis. Experimentally, principal products of n-decane destruction are C2–C9 linear alpha-olefins that are found at ever increasing concentrations with decreasing carbon number, starting with 1-nonene all the way to propene and ethylene, the most abundant products. Successive fragmentation steps of the n-decane primary products lead to the formation of C2–C5 dienes and other hydrocarbons with multiple unsaturated bonds. The consumption rate of n-decane is more abrupt in the methane flame as compared to the gentler decay observed in the ethylene flame. The addition of n-decane in the ethylene flame does not contribute to the formation of soot precursors such as aromatic compounds because the pool of C2–C4 fragments of the baseline flame, playing a key role in aromatic growth, is only marginally affected by n-decane addition. The comprehensive database of stable species of the experimental component of the study is tested by a comparison with the results of modeling the flames using two semi-detailed chemical kinetic mechanisms, Ranzi-mech and JetSurF. Shortcomings of these mechanisms are highlighted for different classes of compounds by comparison of the model results with the experimental data leaving room for future improvements in their formulation.