Direct Measurements of Permittivity of Plasma-Assisted Combustion Using Electrical Capacitance Tomography

The permittivity distribution and the flame development in a closed plasma-assisted combustor were investigated using an electrical capacitance tomography system. The experiments were conducted at a pressure of 1 atm and at different equivalence ratios. I-V curves measured by the Langmuir probe were utilized to estimate the floating potential (-40 to -10 V) and the electron local parameters (T_e and n_e) in the plasma-assisted flames. The results showed that the electron concentration reached the maximum at a location close to the plasma injection point where the primary reaction region of the CH₄-air premixed flame was located. Major species measurement by emission spectrometer combined with the probe measurement revealed that the kinetic enhancement was more significant than the thermal enhancement in the plasma-assisted combustion. Moreover, the dependence of combustion kinetics including electron/ion concentration and temperature on the flame permittivity was verified. The quantitative permittivity data obtained in this study provide a good validation target for modeling of the electric field in plasma-assisted combustion.