Mass Spectrometric Study of Cations in a Non-Sooting Ethylene Flame

Understanding the kinetics and mechanism of formation of charged species in flames is of great importance for the development of ion-sensitive combustion control technologies. The development of predictive models involving ion-molecular reactions, however, is hampered by the lack of experimental data. The paper presents the results of our study of the spatial distribution of cations naturally occurring in a fuel-rich, non-sooting, laminar premixed ethylene/oxygen/argon flame using flame sampling molecular beam mass spectrometry. Particular attention is paid to the interpretation of the obtained mass spectra of cations, which are distorted by the influence of the sampling probe. The reliability of the proposed interpretation of the spectra is confirmed by consistency between the cationic and neutral flame structures. The study focused on cations with the general formula C_xH\(_{y}^{ + }\) (53 < m/z < 165), actively formed in the reaction zone of the fuel-rich flame. Two main mechanisms of their formation are discussed: proton transfer from HCO⁺ and H₃O⁺ (key cations of flame) to neutral intermediates whose mass is 1 amu smaller and gradual increase in the mass of ions in the reactions of lighter C_xH\(_{y}^{ + }\) ions with neutral intermediates having high concentrations in the flame (acetylene, diacetylene, propylene, propyne, etc.).