Photoionization mass speetrometry for the investigation of combustion generated nascent nanoparticles and their relation to laser induced incandescence

摘要

Premixed laminar flat ethylene flames were in vestigated for nascent nanoparticles through photoionization mass speetrometry (PIMS). Using an atmospheric McKenna burner and ethylene air flames coupled to an atmospheric sampling system, within a relatively narrow C/O range two modes of these particles were found, which can be clearly distinguished with regard to their temperature dependence, their reactivity, and their ionization behaviour. Behind a diesel engine the same particles were observed. These results were corroborated using a low pressure ethylene-O2 flame coupled to a high resolution mass spec trometer. In this case, due to a special inlet system, it was possible to operate the flame in a fairly wide C/O range without clogging of the inlet nozzles. This allowed pursu ing the development of particle size distribution functions (PSDF) well into the regime of mature soot. In addition, on the low mass side of the particle spectra measurements with unity resolution were possible and this allowed gaining information concerning their growth mechanism and struc ture. Finally, in an attempt to mimic Laser Induced Incandes cence (LII) experiments the soot-laden molecular beam was exposed to IR irradiation. This resulted in a near complete destruction of nascent particles under LII typical fluences. Small C clusters between 3 and 17 C atoms were found. In addition and with much higher intensities, clusters com prising several hundreds of C atoms were also detected, the latter even at very low fluences when small clusters were totally absent.