Application of an Ion Attachment Mass Spectrometer to Direct Detection of Intermediate Species Formed in Dimethyl Ether-Air and Ethanol-Air Flames

Abstract

Identification of intermediate chemical species in a combustion flame is an important step for obtaining energy with high efficiency from combustion, reducing the toxic emissions released by combustion, and understanding reaction mechanisms in flames. We have developed a unique system based on ion attachment mass spectrometry (IAMS) to identify such intermediates. In this system, the chemical species generated in flames under atmospheric pressure are directly introduced through a sampling cone of a newly developed interface into the ionization chamber (ca. 2 Pa). Then, the species are ionized by Li⁺ ion attachment and introduced into a quadrupole mass spectrometer operating at ca. 1×10^-3 Pa. Intermediate species in flames were successfully detected. Notably, the production of highly toxic environmental pollutants, such as formaldehyde (HCHO) and acetaldehyde (CH₃CHO), were confirmed to be produced during combustion of the promising alternative fuels, dimethyl ether (CH₃OCH₃) and ethanol (CH₃CH₂OH). In addition, by moving the burner position for detecting the species at various positions, the abundance of the species in the flames was observed in two-dimensional distribution profiles. Some correlations were found between the distributions of intermediate species and the flame temperature.