Particle Inception and Growth in Premixed Flames by Photoionization Measurements (Abstract/Poster in convegno)

Type
Label
  • Particle Inception and Growth in Premixed Flames by Photoionization Measurements (Abstract/Poster in convegno) (literal)
Anno
  • 2012-01-01T00:00:00+01:00 (literal)
Alternative label
  • Patrizia Minutolo, Mario Commodo, Lee Anne Sgo, Andrea D'Anna (2012)
    Particle Inception and Growth in Premixed Flames by Photoionization Measurements
    in 34th International Symposium on Combustion, Warsaw, Poland, July 29 - August 3, 2012.
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • Patrizia Minutolo, Mario Commodo, Lee Anne Sgo, Andrea D'Anna (literal)
Note
  • Poster (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
  • Istituto di Ricerche sulla Combustione, CNR, P.le Tecchio 80, 80125 Napoli, Italy University Federico II of Naples, Italy 2IRC-CNR, Italy (literal)
Titolo
  • Particle Inception and Growth in Premixed Flames by Photoionization Measurements (literal)
Abstract
  • Photoionization yields have been measured in earlier works that showed that combustion-generated aerosols produced in flames or by vehicles emit photoelectrons when irradiated with UV light. The authors interpreted such photoelectric activity of combustion-generated aerosols as due to PAHs adsorbed onto carbon particles, which were demonstrated to greatly enhance photoionization yield. Furthermore, investigations of monodisperse carbon and NaCl particles with known amounts of specific PAHs adsorbed on their surfaces showed that the photoionization depends both on the chemical nature of the core particle and on the specific PAHs in the coatings. Photoionization based techniques have high sensitivity and chemical selectivity. These measurements can also provide in situ light absorption of aerosols with extremely low mass concentrations, since the first step in photoelectric charging is the absorption of a photon and the electrical measurements can easily reach higher sensitivity than optical ones. Exploiting the high photoionization yields of combustion-generated aerosols and various aerosols coated with PAHs, concentrations as low as nanograms per cubic meter have been detected measuring the changes in the aerosol charge state produced by photoionization. The high potentiality of photoionization measurements for the analysis of different carbonaceous particles is particularly attractive and can give complementary information to most of nanoparticle characterization methods. In this work, we explore photoionization combined with on-line differential mobility analysis measurements as a diagnostic able to provide size-dependent information on the chemical structure of incipient nanoparticles. On-line measurements using a differential mobility analyzer (DMA) system with sizing capabilities and sensitivity to particles as small as 1 nm is used together with a dilution probe able to fully suppress particle growth processes in the sample line, including particle-particle coagulation and also condensation of volatile species on the surface of particles. Combustion generated particles are sampled in atmospheric pressure premixed ethylene/air flames by a high dilution sampling probe and sent on line to a tube with quartz windows where particles may be irradiated with UV. Changes in the particle charge state, produced by the light source when it is switched on and off, are measured to determine the photoionization yield. First results have been obtained using the fifth harmonic of a Nd-Yag laser (l = 213 nm, 5.82 eV) to irradiate particles generated in a flame with C/O = 0.67 v0 = 10cm/s. This is a slightly sooting flame that, at the height of 15 mm above the burner, produces a bimodal particle size distribution with a first mode at about 3 nm and a second mode centered at about 10 nm. Preliminary results show that particles in the first mode have a higher photoionization yield than the particles in the second mode. This indicates that the two modes are composed by particles with a different carbonaceous structure. In particular, it can be interpreted as an evidence of the formation of small particles with a molecular-like structure which contain aromatic subunits. On the contrary, larger particles have an aromatic structure which is closer to solid graphitic-like structure. Similar measurements in diffusion flames burning methane showed a higher yield for particles measured in the early region of the flame as well as for the smaller particles in the size distribution and were interpreted as due to particlebound PAHs either on the surface or within the particle structure. (literal)
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