The use of high temperature and low oxygen concentration air as the oxidizer for regenerative combustion has become of increasing interest because this technology results in higher thermal efficiency, low energy consumption, and reduced emission of pollutants, such as NO{sub}x and CO{sub}2, and compact size of the equipment. In this study information is provided on the effect of preheating the low oxygen concentration air on the formation and detection of chemical ions and neutral species formed in flames. These ions and species were detected directly using mass spectrometry. Such information also assists in determining the combustion mechanism. The intact ionic species have been detected only at downstream position of the flames. By applying an alkali element (Li{sup}+) ion attachment technique, neutral species, such as Li+-attached ions have been also detected successfully. Three specific flame cases have been examined. They include using normal air (flame I), preheated air (flame II), and preheated air with low (diluted) oxygen concentration in air (flame III). The results show significant change in the spectra of the intact ionic species and the Li{sup}+-adduct neutral species amongst the three flames. The results also show that preheating the combustion air increases the number of chemical species formed in the flames. However, these chemical species decrease with low oxygen concentration (diluted) combustion air.
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