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1D numerical analysis of CO2 vibrational non-equilibrium in supersonic expansions

The CO2 dissociation in supersonic nozzles has recently become of great interest. The non-equilibrium in supersonic nozzles is the key for an efficient CO2 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 CO2 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.