Plasma-assisted gas conversion techniques are widely considered as efficient building blocks in a future energy infrastructure which will be based on intermittent, renewable electricity sources. CO2 dissociation in high-frequency plasmas is of particular interest in carbon capture and utilisation process chains for the production of CO2-neutral fuels. The vibrational excitation of the CO2 molecule plays an important role in the energy efficient dissociation kinetics; however the complete understanding of this mechanism is still unclear. The methodologies used nowadays to model this system are based on strong approximations, due to the complex chemical network and the presence of multiple time and length scales, therefore fast but accurate computational techniques are needed. The state-to-state approach [1] allows to calculate very accurate reaction rates by considering any vibrational level as an individual species. The main problem in calculating the vibrational distribution function for a molecule like CO2 is the large number of levels leading to a huge number of possible transitions between levels. This leads to high computational costs and requires large sets of data, most of which not well known. Therefore, in this work, a reconsideration of the Fokker-Planck (FP) approach [2] which transforms the Master Equation (ME) for the vibrational distribution function (VDF) into a FP equation [3], is examined. In this way the set of quantum numbers is replaced by a continuum energy E, and two coefficients, a diffusion coefficient D(E) and a drift coefficient a(E) are introduced in place of the large number of detailed coefficients. This approach, developed in the past to produce simplified models suitable for analytical solutions, can become more flexible when considered as a basis for numerical models. To this aim, the related transport coefficients must be determined from the chemical rate coefficients. Results are discussed for different values of the key parameter Tv/T0, i.e. the ratio of the vibrational to translational temperature. References [1] T. Kozák, A. Bogaerts, Plasma Sources Sci. Technol. 23 (2014) 045004. [2] V. D. Rusanov, A. A. Fridman, G.V. Sholin, Sov. Phys. Usp. 24 (1981) 447. [3] B. F. Gordiets, “Kinetic processes in gases and molecular lasers”, Routledge, 1988.

A new computational approach to determine the role of vibrational kinetics in low temperature plasmas used for CO2 dissociation

255th National Meeting (2018)

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