Mass-Spectrometric Study of Ion Profiles in Low-Pressure Flames

Abstract

A mass-spectrometric technique for determining ion profiles through low-pressure flames (1–6 mm Hg) has been developed. Typical results are presented for hydrocarbon—oxygen flames which show that the dominant ion is H3O+ and that the concentration of C3H3+, the next most abundant ion, reaches a maximum concentration in the flames ahead of H3O+. A large number of other ions are also identified.

Analysis of the current–voltage curves and saturation currents in burner-stabilised premixed flames with detailed ion chemistry and transport models

“…The peak ion number density is correlated with the maximum heat release rate [11], and varies between 10 16 and 10 17 m −3 for atmospheric flames depending on the fuel and equivalence ratio [12]. Total positive and negative charges decrease along a flame's burned gas, as a result of positive ions recombining with free electrons [10,13,14]. Negative ions, primarily OHand O -2 , are present in the reaction zone of hydrocarbon flames in air, and they are generally attributed to associative and dissociative electron attachment reactions, such as O 2 + e -+ M −− −− O -2 + M and H 2 O + e -−− −− OH -+ H, respectively [15][16][17].…”

“…The accuracy of simulations also relies strongly on the kinetic and transport properties of the charged species. In particular, the chemi-ionization and recombination rate constants are paramount to the quantitative prediction of the total positive and negative charges in a flame [9,13,14,18]. However, the current literature offers widely different values for these rates, showing important contrasts in the presumed temperature dependence [19].…”

“…The kinetic data to determine the contribution of anions to the total negative charge are even more uncertain. Furthermore, neutral radicals CH and O play a crucial role in producing the charged species [13,18,20] and they should be predicted accurately to simulate the concentrations of charge carriers in flames. Unfortunately, many existing kinetic mechanisms show large differences in CH concentrations [21][22][23].…”

New insights into methane-oxygen ion chemistry

“…Compared to other diagnostic techniques, molecular beam mass spectrometry (MBMS) provides high sensitivity and the ability to differentiate between ions and neutrals. MBMS has previously been used to carry out ion measurements in flames [9][10][11][12][13][14][15][16] . Deckers and Van Tiggelen [9][10][11] utilized a mass spectrometer to measure ions in low-pressure acetylene-oxygen flames.…”

“…Deckers and Van Tiggelen [9][10][11] utilized a mass spectrometer to measure ions in low-pressure acetylene-oxygen flames. Calcote and Reuter [12] used MBMS to measure cations in low-pressure ethylene-oxygen flames. Goodings et al [13,14] performed a detailed study of methane ion chemistry by measuring relative cation and anion signals in lean and rich premixed atmospheric Bunsen-type flames, although temperature profiles were not reported.…”