Fast gas heating effects in energy small molecules conversion by pulsed spark discharge plasma

Relevant studies have shown that pulsed spark discharge plasma demonstrates unique advantages in CO
2
splitting, CH
4
dry reforming, and N
2
fixation reactions [1], due to its appropriately high electron density and gas temperature environment. The fast gas heating effect, typically caused by the quenching of electronically and vibrationally excited states in a nanosecond to microsecond scales, has been recommended to play important roles in maintaining highly vibrational-excited states and reducing the energy barrier of Zeldovich reactions [2, 3]. In this paper, the 0D kinetic modeling of pulsed spark discharge plasma ($\mathrm{E} / \mathrm{N}\gt 200 \mathrm{Td}$) is successfully implemented in pure $\mathrm{CO}_2, \mathrm{CH}_4 / \mathrm{CO}_2$ and $\mathrm{N}_2 / \mathrm{O}_2$, respectively, with considering thermal equilibrium equations and reaction enthalpy. It shows that the fast gas heating process in pulsed spark discharges commonly can be divided into two stages: (1) the first gas heating by the rapid relaxation and exothermic state of electronically excited particles (mainly within 200 ns), i.e., $\mathrm{N}_2\left(B^3 \Pi_{\mathrm{g}}, C^3 \Pi_{\mathrm{u}}, a^{12} \Sigma_{\mathrm{u}}^{-}\right)$ in $\mathrm{N}_2 / \mathrm{O}_2$ system while $\mathrm{CO}_2\left(e_1, e_2\right), \mathrm{CO}\left(\mathrm{a}^3 \Pi, \mathrm{a}^{13} \Sigma^{+}\right)$ in pure CO
2
and $\mathrm{CH}_4 / \mathrm{CO}_2$ systems. (2) the second gas heating by the relaxation process of vibrationally excited states (within hundreds of nanoseconds to several microseconds). However, the first gas heating stage dominates in $\mathrm{N}_2 / \mathrm{O}_2$ system while the second gas heating stage is more significant in $\mathrm{CH}_4 / \mathrm{CO}_2$ system and occurs earlier in pure CO
2
system.