Nanosecond Pulsed Plasma Activated C2H4/O2/Ar Mixtures in a Flow Reactor

摘要

The present work combines numerical and experimental efforts to investigate the effect of nanosecond pulsed plasma discharges on the low-temperature oxidation of C_2H_4/O_2/Ar mixtures under reduced pressure conditions. The nonequilibrium plasma discharge is modeled using a one-dimensional framework, employing separate electron and neutral gas temperatures, and using a detailed plasma and combustion chemical kinetic mechanism. Good agreement is seen between the numerical and experimental results, and both results show that plasma enables low-temperature C_2H_4 oxidation. Compared to zero-dimensional modeling, the one-dimensional modeling significantly improves predictions, probably because it produces a more complete physical description (including sheath formation and accurate reduced electric field). Furthermore, the one- and zero-dimensional models show very different reaction pathways, using the same chemical kinetic mechanism and thus suggest different interpretations of the experimental results. Two kinetic mechanisms (HP-Mech and USC Mech-Ⅱ) are examined in this study. The modeling results from HP-Mech agree better with the experimental results than those of USC Mech-Ⅱ because USC Mech-Ⅱ does not include the OH + C_2H_4 = CH_2CH_2OH reaction pathway. The model shows that 75-77% of the input pulse energy is consumed during the breakdown process in electron impact dissociation, excitation, and ionization reactions, which efficiently produce reactive radical species, fuel fragments, and excited species. The modeling results using HP-Mech reveal that reactions between O(~1D) and C_2H_4 generate 24% of OH, 19% of HCO, 60% of CH_3,63% of CH_2, and 17% of CH_2O. These in turn significantly enhance hydrocarbon oxidation, since 83% of CO comes from HCO and 53% of CO_2 comes from CH_2 under the present low-temperature environment and short time scale.