Identification of combustion intermediates in isomeric fuel-rich premixed butanol–oxygen flames at low pressure

Laminar premixed low-pressure flames fueled by either one of the four isomers of butanol were investigated by a molecular-beam photoionization mass spectrometer using vacuum ultraviolet (VUV) synchrotron radiation as the ionization source. The photoionization efficiency (PIE) spectra of most flame intermediates were measured between 7.75 and 11.00 eV. By comparing the resulting PIE spectra to known ionization energies (IEs) or known PIE spectra of pure substances, most hydrocarbon and oxygenated combustion intermediates, including some radicals, in the mass range from m / z = 15 to 106 were assigned and identified in the four butanol flames. The results show that the higher-mass oxygenated species in butanol flames are strongly affected by the fuel structure, while many hydrocarbon isomers appear almost independent of the fuel structure. The respective dissociation mechanisms of the fuels, including complex fission, simple fission, and H-atom abstraction, are in good agreement with previous results from nonpremixed butanol flames.