N2O oxidized combustion of ethylene: Detailed laminar flame structure and the significance of oxidizer decomposition kinetics for modeling

We report the detailed flame structure of an N2O oxidized, fuel-rich flame of ethylene (C2H4) at an equivalence ratio of 1.2, measured with double-imaging photoelectron photoion coincidence spectroscopy (i2PEPICO) using synchrotron vacuum ultraviolet photoionization. We analyze the oxidizer decomposition and the intermediate chemistry with a focus on isomer branching ratios of CHNO and on the abundantly produced HCN (hydrogen cyanide). A detailed mechanism is composed that comprises recently reported reaction rates for N2O decomposition and detailed hydrocarbon chemistry and nitrogen chemistry. The new mechanism is based on the Aramco 3.0 chemistry set. The predictive accuracy for both main species mole fractions and intermediate mole fractions, was significantly improved. The mechanism shows excellent agreement with the flame measurements and improves upon existing mechanisms. As a first, we were able to detect, separate and assign the signals of two of the CHNO isomers and tentatively assign an isomer branching ratio to HCNO (fulminic acid) and HNCO (isocyanic acid). H radicals show significant activity throughout the whole reaction network in the provided analysis. They interact in the decomposition of the fuel and act as a driver of intermediate formation and destruction. The presented data is a first detailed look at the fuel and oxidizer decomposition for these flames using synchrotron photoionization methods and delivers valuable data for the development and validation of chemical kinetics mechanisms. We conclude that the decomposition kinetics of N2O play a significant role in the remaining kinetics of the combustion process under the reported flame conditions and influence the whole reaction network down to intermediate species.