Non-equilibrium low-temperature plasma-assisted combustion of iso-octane: Perturbing pyrolysis and oxidation kinetics

In this study, a plasma-coupled flow reactor facility is used to examine the effects of non-equilibrium low-temperature plasmas on perturbing the pyrolysis and oxidation kinetics of iso-octane. Experiments were performed in highly dilute reactive mixtures of nitrogen, at near isothermal conditions for temper-atures ranging from 523 K to 1203 K. Experiments cumulatively demonstrated enhanced chemical reac-tivity with the plasma for temperatures below 900 K, and a lowering of the hot-ignition temperature. Detailed kinetic insight was derived from a 0D plasma-coupled kinetic model, utilizing a constructed mechanism that combined both plasma-specific chemistry and the neutral combustion chemistry. For pyrolysis conditions, the model displayed relatively good agreement with fuel consumption and the for-mation of most intermediates compared to the experimental data, demonstrating the model is able to accurately predict primary radical formation from the plasma directly interacting with the fuel. Enhanced reactivity was attributed to collisional quenching of excited-states of N 2 with fuel, which led to efficient fuel fragmentation and enhancement of the H-radical flux. For oxidation conditions, the model displayed satisfactory agreement with the experiments. Model predictions were able to accurately predict fuel con-sumption and most intermediate speciation data for T > 800 K, but most discrepancies were towards T < 800 K in particular with oxygenated intermediates. In the presence of oxygen, plasma effects were pre-dominantly spent on efficient enhancement of O-and H-radical fluxes, leading to further fuel fragmenta-tion and initiation of both the OH-and HO2-radical pools. Subsequent reactivity of iso-octane was then dictated by the response of the temperature-dependent neutral chemistry. At low-temperatures ( T = 643 K), enhanced fuel radicals and O2-additon chemistry lead to the formation of oxygenated species, while at intermediate temperatures ( T = 843 K) net decrease in OH-radical reactivity led to an increase in hydro-carbon speciation. Near the self-ignition threshold ( T = 1163 K), radicals generated by high-temperature branching reactions dominate the oxidation process and effectively ignition. This study ultimately demon-strated that the enhancement of radicals afforded by the plasma causes a deviation in known understand-ing of iso-octane kinetics in some regards and warrants future studies to reconcile these discrepancies.& COPY; 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

In this study, the effects of non-equilibrium low-temperature plasmas on the pyrolysis and oxidation kinetics of iso-octane were examined using a plasma-coupled flow reactor facility. The results showed that the plasma enhanced the chemical reactivity and lowered the hot-ignition temperature below 900 K. A 0D plasma-coupled kinetic model was used to obtain detailed kinetic insight, and it displayed good agreement with the experimental data for fuel consumption and intermediate formation during pyrolysis conditions. The model also had satisfactory agreement with the experiments for oxidation conditions, except for discrepancies observed at lower temperatures.