Chemi-ionization in Shock-Induced Hydrocarbon Combustion I. Ion Concentrations in Methane/Air

Abstract

Abstract An experimental and analytical study of chemi-ionization processes in reacting methane/air mixtures was carried out at temperatures up to 2000 °K. Using the reflected shock region as a homogeneous reaction zone, Langmuir probe measurements were performed in a conventional shock tube to determine positive ion concentrations and their induction times. The results are analyzed by means of a numerical study using an ionization mechanism incorporated into recently established methane oxidation mechanisms, and the calculated and experimental ion concentrations are comparable primarily at higher temperatures. Various ionization mechanisms are discussed. The ion-concentrations are compared to those obtained from flame studies at similar conditions, and although ion concentrations in homogeneous systems are higher, the ion production rates are found to be comparable.