AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
High-Resolution Mass Spectrometry of Soot Nuclei formed in a Laminar Premixed Flame Diffusionally Charged at Atmospheric Pressure
FRANCESCO CARBONE, Manjula Canagaratna, Andrew Lambe, Paola Massoli, John Jayne, Douglas Worsnop, Alessandro Gomez, Yale University
Abstract Number: 569 Working Group: Combustion
Abstract Flame-generated soot nuclei and precursors were analyzed in the mass to charge ratio range up to 3000 Th, to bridge the gap between the gas and the particle phase and take advantage of recent advances in both mass spectrometry and rapid dilution sampling and diffusional charging techniques. Elemental compositions of both negatively and positively charged flame products were obtained by coupling a highly sensitive Atmospheric Pressure Interface Time-of-Flight (APi-TOF, Tofwerk AG) Mass Spectrometer with mass resolving power in excess of 3000, to a horizontal tube dilution probe. The analyte was directly sampled from a moderately sooting premixed flame that had been the object of previous detailed studies. The flame was stabilized on a honeycomb burner fueled by an ethylene/air mixture with a C/O ratio of 0.69 and unburnt gas velocity of 58.7 mm/s. The sampled flame products were quickly diluted in nitrogen and transported to the APi-TOF inlet while diffusional charging was provided at atmospheric pressure by either the flame chemi-ions themselves or by collisions with bipolar ions purposely seeded in the dilution flow. Four dilution levels were used to investigate the low-temperature evolution of material in the path to the APi-TOF inlet following flame sampling. Samples were extracted at several heights above the burner (HAB) to track soot precursors and nuclei growth in the flame. The high resolution measured mass spectra revealed the chemical complexity of the flame pyrolysis and chemi-ionization products and the presence of hydrocarbon molecules that contain nitrogen and oxygen atoms. Patterns in the mass spectra measured under different conditions are investigated to discriminate between chemical reaction and physical condensation growth mechanisms. A comparison of these results with those obtained with Differential Mobility Analysis in recent studies is being evaluated to assess the self-consistency of disparate techniques.