No abstract

The CO 2 dissociation in supersonic nozzles has recently become of great interest. The non-equilibrium in supersonic nozzles is the key for an efficient CO 2 dissociation. This study has two objectives. First, the development of one dimensional models is targeted. Second, the influence of different steering conditions and design parameters on CO 2 vibrational non-equilibrium have been studied within the framework of developed models. In this paper, a simple method, the semi-analytical model, is presented which despite being very simple and fast (few seconds) can perform as well as its more sophisticated counterparts. For validation purposes we also developed and applied a quasi-1D numerical model. The influence of the expansion length, as a design parameter, on the non-equilibrium is investigated. It is found that there is no optimal Mach number as long as the expansion length is carefully chosen. The higher the Mach number, the more significant the non-equilibrium. The effect of inlet parameters such as the gas temperature, the pressure and the electron temperature have been studied. The highest non-equilibrium is obtained when a low inlet temperature is taken provided that an appropriate expansion length is used. The inlet pressure is shown to have theoretically no influence on the state of non-equilibrium as long as the expansion length is accordingly chosen. Finally, the study of the impact of the electron temperature on the vibrational distribution function indicates that a continuous pooling of higher vibrational states can be obtained in the diverging part of the nozzle. The higher the electron temperature, the higher the yield.

Plasma assisted CO 2 dissociation has recently been the topic of many studies. The production of chemical fuels from environmentally unfriendly CO 2 through supersonic nozzles is one of the most prominent approaches under investigation. However, the experiments show that the theoretical conversion rates are far away from being achieved. In this study, two-dimensional fully coupled cases are investigated. This brings insights about how the CO 2 dissociation can be improved; mainly by a correct design of nozzles. The proper shape of a nozzle is a fundamental aspect to be taken into account numerically and in experiments to avoid undesirable phenomena such as the occurrence of shocks. The proper design of the nozzle shape leads to a shock-free flow being uniform at the nozzle outlet. A high degree of cooling can be achieved in a shock-free nozzle. Moreover it is shown that there is no optimal value for Mach number provided that the nozzles are sized properly. If the sizing is done correctly, it is found that higher Mach numbers lead to higher degree of non-equilibrium and thereby to higher dissociation rate. The sizing of the nozzle to maximize the departure from equilibrium in the nozzle is the final key of an efficient CO 2 dissociation. Finally, the results are compared with those of a semi-analytical method to conclude that if the nozzle is conceived in a proper way, simpler approaches can also give satisfactory results.

The effect of shock-free supersonic expansion on the dissociation of CO 2 with elevated vibrational temperatures is investigated. It is found that expansioncooling not only favors dissociation but also obstructs recombination. The dissociation generated by VV ladder climbing is investigated using the two different model-types: 1D Full Numerical (Fu-N) and Semi-Analytical (S-An). The Fu-N gives a more complete self-consistent description but needs about 1000 times longer convergence

A self-consistent model giving insights on the flow-chemistry interplay in supersonic nozzles is presented. It is shown that the change of flow properties, caused by CO 2 dissociation, enhances the cooling potential. This results in positive feedback boosting the CO 2 dissociation. The focus of this study is on the second stage of a tandem-construction, that is, the expanding afterglow. The first stage of activating the CO 2 vibrational states can be done by combustion or a plasma treatment. The expansion in the second stage triggers the vibrational-vibrational