High temperature coronas in air and flue gas from LPG combustion: Current-voltage characteristics, ion mobilities and free electrons

Positive and negative corona discharges were studied at atmospheric pressure in a tube-wire geometry with a tube diameter of 150 mm. Current-voltage characteristics (CVCs) were measured both in air and in flue gas produced with a liquefied petroleum gas (LPG) burner, covering temperatures from ambient up to 1073 K. Corona operation was stable over the whole temperature range with positive polarity and up to 973 K with negative polarity. Based on a detailed analysis of the original CVC measurements, new insights on the temperature-dependent mobility of gas ions, on the occurrence of free electrons and on the electronic current contribution are presented. Deviations from the Townsend theory of CVCs can be ascribed to the lifetime-dependency of ion mobility caused by the formation of cluster ions. The contribution from free electrons is found to depend on temperature and tube radius.