Conclusions
We have determined the rate constants of the potassium ionization process A→A++e− in the flames of 2H2+O2+X (Ar, He) mixtures on the temperature interval 1500–2500° K. The activation energy of this process is close to the ionization potential of potassium (100 kcal).
In our experiments the rate of ion formation in the front of a hydrogen flame seeded with potassium exceeded the purely thermal ionization rate by 0.5–2 orders. The presumed cause is “recombination” ionization of the potassium in the flame front, for example, K+O+O→K++O2+e−. This is confirmed by the intensification of ionization in the reaction zone in the presence of an excess of oxygen in homogeneous H2-air and H2−O2−(He, Ar) mixtures with alkali impurities.
At T=1700° K the recombination coefficient for electrons and potassium ions is close to 1·10−8 cm3·sec−1. For a more precise determination it is necessary to know the frequency of electron capture by molecules and atoms under the experimental conditions.
Experiments on thermal ionization in turbulent flames confirm the earlier conclusion concerning the important role of mass transfer in the chemi-ionization of hydrocarbon flames.
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Fizika Goreniya i Vzryva, Vol. 6, No. 1, pp. 37–48, 1970
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Semenov, E.S., Sokolik, A.S. Thermal and chemical ionization in flames. Combust Explos Shock Waves 6, 33–43 (1970). https://doi.org/10.1007/BF02044894
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DOI: https://doi.org/10.1007/BF02044894