N-heptane low temperature oxidation kinetics in nanosecond-pulsed plasma discharges

The present study seeks to understand the kinetics of plasma assisted low temperature oxidation of n-heptane/O₂/Ar mixtures in a nanosecond repetitively pulsed dielectric barrier discharge by measuring both steady state and time-dependent species and temperature using micro-GC sampling and in situ tunable diode laser absorption spectroscopy (TDLAS). The influence of energy transfer via excited species and direct electron impact dissociation on intermediate and species production has been explored by varying plasma discharge frequency, and argon and oxygen concentrations. Results show a linear dependence of fuel consumption and product formation on the increase of plasma pulse frequency, demonstrating the decoupling of the kinetic processes between plasma assisted fuel oxidation and low temperature ignition chemistry at the burst discharge conditions. Larger fuel dissociation rates are observed with greater argon than oxygen concentrations, suggesting that higher electron densities and fuel dissociation via direct impact by excited argon at larger argon dilution are more effective than direct oxygen dissociation due to electron impact. Numerical comparisons with time-dependent measurements reveal an overprediction of fuel consumption and water production and a significant underprediction of formaldehyde, suggesting missing reaction pathways between plasma produced excited species and fuel and intermediate species.