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Shao C, Wang Q, Zhang W, Bennett A, Li Y, Guo J, Im HG, Roberts WL, Violi A, Sarathy SM. Elucidating the polycyclic aromatic hydrocarbons involved in soot inception. Commun Chem 2023; 6:223. [PMID: 37845500 PMCID: PMC10579345 DOI: 10.1038/s42004-023-01017-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Accepted: 09/29/2023] [Indexed: 10/18/2023] Open
Abstract
Polycyclic aromatic hydrocarbons are the main precursors to soot particles in combustion systems. A lack of direct experimental evidence has led to controversial theoretical explanations for the transition from gas-phase species to organic soot clusters. This work focuses on sampling infant soot particles from well-defined flames followed by analysis using state-of-the-art mass spectrometry. We found that PAH molecules present in soot particles are all stabilomers. Kinetic Monte Carlo simulations and thermodynamic stability calculations further identify the detected PAHs as peri-condensed and without aliphatic chains. Van der Waals forces can easily link PAHs of such size and shape to form PAH dimers and larger clusters under the specified flame conditions. Our results provide direct experimental evidence that soot inception is initiated by a physical process under typical flame conditions. This work improves our understanding of aerosol particulates, which has implications for their environmental and climate change impacts.
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Affiliation(s)
- Can Shao
- King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center, Thuwal, 23955-6900, Saudi Arabia.
| | - Qi Wang
- Department of Mechanical Engineering, University of Michigan, 2350 Hayward St, Ann Arbor, MI, 48109-2125, USA
| | - Wen Zhang
- King Abdullah University of Science and Technology (KAUST), Core Labs, Thuwal, 23955-6900, Saudi Arabia.
| | - Anthony Bennett
- King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center, Thuwal, 23955-6900, Saudi Arabia
| | - Yang Li
- King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center, Thuwal, 23955-6900, Saudi Arabia
- Science and Technology on Combustion, Internal Flow and Thermostructure Laboratory, School of Astronautics, Northwestern Polytechnical University, 710072, Xi'an, China
| | - Junjun Guo
- King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center, Thuwal, 23955-6900, Saudi Arabia
| | - Hong G Im
- King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center, Thuwal, 23955-6900, Saudi Arabia
| | - William L Roberts
- King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center, Thuwal, 23955-6900, Saudi Arabia
| | - Angela Violi
- Department of Mechanical Engineering, University of Michigan, 2350 Hayward St, Ann Arbor, MI, 48109-2125, USA
- Department of Chemical Engineering, University of Michigan, 2350 Hayward St, Ann Arbor, MI, 48109-2125, USA
- Chemical Engineering and Biophysics Program, University of Michigan, 930 N. University Ave, Ann Arbor, MI, 48109-1055, USA
| | - S Mani Sarathy
- King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center, Thuwal, 23955-6900, Saudi Arabia.
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Adkins EM, Miller JH. Extinction measurements for optical band gap determination of soot in a series of nitrogen-diluted ethylene/air non-premixed flames. Phys Chem Chem Phys 2015; 17:2686-95. [DOI: 10.1039/c4cp04452e] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The critical PAH size for particle inception in the soot formation mechanism has been defined by correlating the experimentally determined optical band gap with calculated HOMO–LUMO gaps for a range of pericondensed PAHs. The observed optical band gap is consistent with a PAH of about 14 rings.
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Affiliation(s)
- Erin M. Adkins
- Department of Chemistry
- George Washington University
- Washington
- USA
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Koley D, Arunan E, Ramakrishnan S. Computational investigations on covalent dimerization/oligomerization of polyacenes: is it relevant to soot formation? J Comput Chem 2012; 33:1762-72. [PMID: 22610914 DOI: 10.1002/jcc.23014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Revised: 04/23/2012] [Accepted: 04/24/2012] [Indexed: 01/17/2023]
Abstract
We have postulated a novel pathway that could assist in the nucleation of soot particles through covalent dimerization and oligomerizations of a variety of PAHs. DFT calculations were performed with the objective of obtaining the relative thermal stabilities and formation probabilities of oligomeric species that exploit the facile dimerization that is known to occur in linear oligoacenes. We propose that the presence of small stretches of linear oligoacence (tetracene or longer) in extended PAH, either embedded or tethered, would be adequate for enabling the formation of such dimeric and oligomeric adducts; these could then serve as nuclei for the growth of soot particles. Our studies also reveal the importance of π-stacking interactions between extended aromatic frameworks in governing the relative stabilities of the oligomeric species that are formed.
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Affiliation(s)
- D Koley
- Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, Karnataka, India.
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Abstract
Soot formation in a methane air turbulent jet diffusion flame is investigated numerically using a semi-empirical model. The temperature, density and species (the soot precursor C2H2) fields are calculated using detailed chemical kinetic mechanism based on the flamelet library approach. The influence of pressure on the soot formation and the behavior of the semi-empirical model in different flame situations are investigated. It is found that the flame shape and the flame temperature can be well predicted by the flamelet library approach. The calculated soot yield is mostly sensitive to the soot surface growth rate and the increase of pressure. The increase of pressure leads to the increase of soot surface growth rate and therefore to the increase of soot volume fraction. By adjusting a model constant in the soot surface growth rate, the soot emissions in both pressure p = 1 atm and p = 3 atm are properly simulated by the current semi-empirical soot model.
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