Flame ions

Green and Sugden (19) identify masses 33, 43, 45, and 53 as input ions-—i.e., those produced in the sampling systems other ions are natural flame ions, except mass 15 which could not be classified. f> Only observed when HBr added (12). 

The following reactions have been suggested (9) to account for the oxidation of the flame ions... 

Ion-Molecule Reactions in Nonhydrocarbon Flames. Ion-molecule reactions which play important parts in flame ionization phe-... 

CA 65, 19920 (1966) (Direct recording of flame ions on photographic emulsion s)... 

R = Et, Pr, or Bu) are sufficiently volatile for g.l.c. analysis. A flame-ion ization-fiame-emission apparatus for the specific determination of organo-phosphorus compounds has been described. ... 

Burtscher, H. (1992) Measurement and characteristics of combustion aerosols with special consideration of photoelectric charging by flame ions, J. Aerosol Sci. 23, 549-595. 

When the count of flame ions was followed as a function of distance from the reaction zone, it was found that the majority of hydrocarbon ions rose and fell together, but that mass 19 (H3O+) rose slightly less rapidly and fell very much more slowly, so that after a few millimetres it was effectively the only ion. The earliest ion to be formed was found to be mass 29, supposed to be CHO+ which reached its maximum value close to the maximum rate of increase of H30+. ... 

The dominant flame ion, H3O+, appears rapidly in the reaction zone, and in such large amounts that it is probably produced by a proton exchange reaction between a precursor ion and water. Calcote, on... 

A FIGURE 7.21 Placed in a flame, ions of each alkali metal emit light of a characteristic wavelength. 

Originally, studies of ionization in flames were motivated by the observation that in hydrocarbon flames, the ion concentration far exceeds the value expected if ionization were due to thermal processes alone (see Table I). The objectives of these studies were to explain the source of nonequilibrium ionization and to explore links between flame ionization and the mechanism of flame propagation. An explanation of the source of flame ions was found in the process of chemi-ionization. This led to further studies of the details of ionic reactions which occur in flames and of flame reactions which can be induced by the addition of foreign elements. 

Fig. 4. Typical flame ion profiles. Stoichiometric acety-lene/oxygen pressure, 1 Torr adiabatic flame temperature, 2500°K total flow, 70 ml sec" (STP) burner diameter, 15cm.

It is useful to categorize flame ion phenomena according to origin. 

Attainment of equilibrium downstream of flame fronts makes it possible to use flames as media for studying high-temperature thermodynamics. Equilibrium may be approached via collisional ionization or chemi-ionization. When small concentrations of alkali metals are added to flames of low ion content, e.g., hydrogen or carbon monoxide flames, ions are produced by collisional reactions ... 

The positive-ion-molecule reactions in flames can be conveniently divided into those reactions which occur between naturally occurring flame ions and those produced by the addition of other elements, usually metals. 

In summary, studies of natural flame ion-molecule reactions have given us a reasonably clear picture of which reactions are occurring. With more detailed studies of ionization, along with determination of neutral species concentrations, flames will continue to offer a fertile field for studying ion-molecule reactions at high temperatures. 

Recent work by Addecott and Nutt has indicated an interesting correlation between the ion concentration produced by the addition of various metal salts to fuel-rich, smoky flames and their ability to reduce smoke. Since flame ions of the type have been postulated as the... 

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