Towards a kinetic understanding of the NOx sensitization effect on unsaturation hydrocarbons: A case study of ethylene/nitrogen dioxide mixtures

Ignition delay time (IDT) measurements for ethylene (C2H4)/nitrogen dioxide (NO2)/oxygen/argon mixtures with various blending ratios of NO2/C2H4 = 0/100, 15/85 and 50/50 were performed in a shock tube. The sensitization effect of NO2 on C2H4 ignition was investigated at pressures ranging from 1.2 to 10 atm, in the temperature range 920–1780 K, and at equivalence ratios from 0.5 to 2.0. Similar to our recent studies of NO2 effects on CH4 and C2H6 ignition (Deng et al., 2016; Deng et al., 2017), the effect of NO2 addition on measured IDTs of the unsaturated hydrocarbon C2H4 also exhibits both temperature- and pressure- dependences. NO2 addition generally promotes the reactivity of ethylene and the promotion effect is more pronounced for the mixtures with high NO2 content at higher pressures (p > 4.0 atm), at lower temperatures (T   1250 K). A detailed kinetic mechanism of C2H4/NO2 was proposed by refining critical reactions through incorporating ab-initio calculations from this study and recently published rate constant data. This mechanism is capable of reproducing the new data reported in this work and literature ones as well and has thus been used to perform sensitivity and flux analyses to kinetically interpret the interaction of NO2 with C2H4.