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Title: Critical Assessment of Photoionization Efficiency Measurements for Characterization of Soot-Precursor Species

Abstract

We present a critical evaluation of photoionization efficiency (PIE) measurements coupled with aerosol mass spectrometry for the identification of condensed soot-precursor species extracted from a premixed atmospheric-pressure ethylene/oxygen/nitrogen flame. Definitive identification of isomers by any means is complicated by the large number of potential isomers at masses likely to comprise particles at flame temperatures. This problem is compounded using PIE measurements by the similarity in ionization energies and PIE-curve shapes among many of these isomers. Nevertheless, PIE analysis can provide important chemical information. For example, our PIE curves show that neither pyrene nor fluoranthene alone can describe the signal from C 16H 10 isomers and that coronene alone cannot describe the PIE signal from C 24H 12 species. A linear combination of the reference PIE curves for pyrene and fluoranthene yields good agreement with flame-PIE curves measured at 202 u, which is consistent with pyrene and fluoranthene being the two major C 16H 10 isomers in the flame samples, but does not provide definite proof. The suggested ratio between fluoranthene and pyrene depends on the sampling conditions. We calculated the values of the adiabatic-ionization energy (AIE) of 24 C 16H 10 isomers. Despite the small number of isomers considered, themore » calculations show that the differences in AIEs between several of the isomers can be smaller than the average thermal energy at room temperature. The calculations also show that PIE analysis can sometimes be used to separate hydrocarbon species into those that contain mainly aromatic rings and those that contain significant aliphatic content for species sizes investigated in this study. Our calculations suggest an inverse relationship between AIE and the number of aromatic rings. We have demonstrated that further characterization of precursors can be facilitated by measurements that test species volatility.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2];  [1];  [1];  [3];  [3]; ORCiD logo [2];  [1]
  1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  2. Univ. of Michigan, Ann Arbor, MI (United States)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1365807
Report Number(s):
SAND-2017-5882J
Journal ID: ISSN 1089-5639; 653852
Grant/Contract Number:
AC04-94AL85000
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Volume: 121; Journal Issue: 23; Journal ID: ISSN 1089-5639
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Johansson, K. Olof, Z?dor, Judit, Elvati, Paolo, Campbell, Matthew F., Schrader, Paul E., Richards-Henderson, Nicole K., Wilson, Kevin R., Violi, Angela, and Michelsen, Hope A. Critical Assessment of Photoionization Efficiency Measurements for Characterization of Soot-Precursor Species. United States: N. p., 2017. Web. doi:10.1021/acs.jpca.7b02992.
Johansson, K. Olof, Z?dor, Judit, Elvati, Paolo, Campbell, Matthew F., Schrader, Paul E., Richards-Henderson, Nicole K., Wilson, Kevin R., Violi, Angela, & Michelsen, Hope A. Critical Assessment of Photoionization Efficiency Measurements for Characterization of Soot-Precursor Species. United States. doi:10.1021/acs.jpca.7b02992.
Johansson, K. Olof, Z?dor, Judit, Elvati, Paolo, Campbell, Matthew F., Schrader, Paul E., Richards-Henderson, Nicole K., Wilson, Kevin R., Violi, Angela, and Michelsen, Hope A. Thu . "Critical Assessment of Photoionization Efficiency Measurements for Characterization of Soot-Precursor Species". United States. doi:10.1021/acs.jpca.7b02992. https://www.osti.gov/servlets/purl/1365807.
@article{osti_1365807,
title = {Critical Assessment of Photoionization Efficiency Measurements for Characterization of Soot-Precursor Species},
author = {Johansson, K. Olof and Z?dor, Judit and Elvati, Paolo and Campbell, Matthew F. and Schrader, Paul E. and Richards-Henderson, Nicole K. and Wilson, Kevin R. and Violi, Angela and Michelsen, Hope A.},
abstractNote = {We present a critical evaluation of photoionization efficiency (PIE) measurements coupled with aerosol mass spectrometry for the identification of condensed soot-precursor species extracted from a premixed atmospheric-pressure ethylene/oxygen/nitrogen flame. Definitive identification of isomers by any means is complicated by the large number of potential isomers at masses likely to comprise particles at flame temperatures. This problem is compounded using PIE measurements by the similarity in ionization energies and PIE-curve shapes among many of these isomers. Nevertheless, PIE analysis can provide important chemical information. For example, our PIE curves show that neither pyrene nor fluoranthene alone can describe the signal from C16H10 isomers and that coronene alone cannot describe the PIE signal from C24H12 species. A linear combination of the reference PIE curves for pyrene and fluoranthene yields good agreement with flame-PIE curves measured at 202 u, which is consistent with pyrene and fluoranthene being the two major C16H10 isomers in the flame samples, but does not provide definite proof. The suggested ratio between fluoranthene and pyrene depends on the sampling conditions. We calculated the values of the adiabatic-ionization energy (AIE) of 24 C16H10 isomers. Despite the small number of isomers considered, the calculations show that the differences in AIEs between several of the isomers can be smaller than the average thermal energy at room temperature. The calculations also show that PIE analysis can sometimes be used to separate hydrocarbon species into those that contain mainly aromatic rings and those that contain significant aliphatic content for species sizes investigated in this study. Our calculations suggest an inverse relationship between AIE and the number of aromatic rings. We have demonstrated that further characterization of precursors can be facilitated by measurements that test species volatility.},
doi = {10.1021/acs.jpca.7b02992},
journal = {Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory},
number = 23,
volume = 121,
place = {United States},
year = {Thu May 18 00:00:00 EDT 2017},
month = {Thu May 18 00:00:00 EDT 2017}
}

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  • To clarify the mechanism of soot formation in diffusion flames of liquid fuels, measurements of soot and its precursors were carried out. Sooting diffusion flames formed by a small pool combustion equipment system were used for this purpose. Benzene and hexane were used as typical aromatic and paraffin fuels. A laser-induced fluorescence (LIF) method was used to obtain spatial distributions of polycyclic aromatic hydrocarbons (PAHs), which are considered as soot particles. Spatial distributions of soot in test flames were measured by a laser-induced incandescence (LII) method. Soot diameter was estimated from the temporal change of LII intensity. A region ofmore » transition from PAHs to soot was defined from the results of LIF and LII. Flame temperatures, PAH species, and soot diameters in this transition region were investigated for both benzene and hexane flames. The results show that though the flame structures of benzene and hexane were different, the temperature in the PAHs-soot transition region of the benzene flame was similar to that of the hexane flame. Furthermore, the relationship between the PAH concentrations measured by gas chromatography in both flames and the PAH distributions obtained from LIF are discussed. It was found that PAHs with smaller molecular mass, such as benzene and toluene, remained in both the PAHs-soot transition and sooting regions, and it is thought that molecules heavier than pyrene are the leading candidates for soot precursor formation. (author)« less
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  • A model of laminar, soot-laden ethene diffusion flames has been developed and compared with measurements in nonsooting and sooting flames. Concentrations of stable gas-phase species were measured with mass spectrometry; laser-induced fluorescence was used to measure the OH concentrations. A system of elementary reactions was used to describe the gas-phase chemistry. The model incorporated a simple description of the growth of soot which assumed that acetylene was the only growth species. Soot formation was coupled with the flame chemistry via the loss of acetylene and OH on soot and the production of CO during soot oxidation. The model predicted mostmore » of the gas-phase species quite well, with the exception of OH. The loadings of soot in the flames were reproduced adequately, although less success was achieved in predicting the transition from nonsooting to sooting conditions. Details concerning the products of soot oxidation by OH were found to be important with regard to the flame chemistry. The inclusion of soot in the flame model had a significant impact on the predicted structure of the flame as seen in changes to the formation and destruction rates of OH on the fuel side of the flame. The rate of OH reaction with soot in the midregion of the flame was small compared with the rate of reaction of OH with CO. However, the two rates became comparable in the soot burnout zone.« less