On the formation and early evolution of soot in turbulent nonpremixed flames

Handle URI:
http://hdl.handle.net/10754/562043
Title:
On the formation and early evolution of soot in turbulent nonpremixed flames
Authors:
Bisetti, Fabrizio ( 0000-0001-5162-7805 ) ; Blanquart, Guillaume; Müeller, Michael E.; Pitsch, Heinz G.
Abstract:
A Direct Numerical Simulation (DNS) of soot formation in an n-heptane/air turbulent nonpremixed flame has been performed to investigate unsteady strain effects on soot growth and transport. For the first time in a DNS of turbulent combustion, Polycyclic Aromatic Hydrocarbons (PAH) are included via a validated, reduced chemical mechanism. A novel statistical representation of soot aggregates based on the Hybrid Method of Moments is used [M.E. Mueller, G. Blanquart, H. Pitsch, Combust. Flame 156 (2009) 1143-1155], which allows for an accurate state-of-the-art description of soot number density, volume fraction, and morphology of the aggregates. In agreement with previous experimental studies in laminar flames, Damköhler number effects are found to be significant for PAH. Soot nucleation and growth from PAH are locally inhibited by high scalar dissipation rate, thus providing a possible explanation for the experimentally observed reduction of soot yields at increasing levels of mixing in turbulent sooting flames. Furthermore, our data indicate that soot growth models that rely on smaller hydrocarbon species such as acetylene as a proxy for large PAH molecules ignore or misrepresent the effects of turbulent mixing and hydrodynamic strain on soot formation due to differences in the species Damköhler number. Upon formation on the rich side of the flame, soot is displaced relative to curved mixture fraction iso-surfaces due to differential diffusion effects between soot and the gas-phase. Soot traveling towards the flame is oxidized, and aggregates displaced away from the flame grow primarily by condensation of PAH on the particle surface. In contrast to previous DNS studies based on simplified soot and chemistry models, surface reactions are found to contribute barely to the growth of soot, for nucleation and condensation processes occurring in the fuel stream are responsible for the most of soot mass generation. Furthermore, the morphology of the soot aggregates is found to depend on the location of soot in mixture fraction space. Aggregates having the largest primary particles populate the region closest to the location of peak soot growth. On the contrary, the aggregates with the largest number of primary particles are located much further into the fuel stream. © 2011 The Combustion Institute.
KAUST Department:
Clean Combustion Research Center; Physical Sciences and Engineering (PSE) Division; Mechanical Engineering Program; Reactive Flow Modeling Laboratory (RFML)
Publisher:
Elsevier
Journal:
Combustion and Flame
Issue Date:
Jan-2012
DOI:
10.1016/j.combustflame.2011.05.021
Type:
Article
ISSN:
00102180
Sponsors:
The authors gratefully acknowledge funding from the Strategic Environmental Research and Development Program (SERDP) and the National Aeronautics and Space Administration (NASA). This research was supported in part by the National Science Foundation (NSF) through TeraGrid resources provided by the Texas Advanced Computing Center (TACC) under Grant No. TG-CTS090021. M.E.M. gratefully acknowledges support of the National Defense Science and Engineering Graduate (NDSEG) fellowship program. The authors would like to thank Dr. Pepiot-Desjardins for her help in reducing the chemical mechanism.
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division; Mechanical Engineering Program; Clean Combustion Research Center

Full metadata record

DC FieldValue Language
dc.contributor.authorBisetti, Fabrizioen
dc.contributor.authorBlanquart, Guillaumeen
dc.contributor.authorMüeller, Michael E.en
dc.contributor.authorPitsch, Heinz G.en
dc.date.accessioned2015-08-03T09:43:28Zen
dc.date.available2015-08-03T09:43:28Zen
dc.date.issued2012-01en
dc.identifier.issn00102180en
dc.identifier.doi10.1016/j.combustflame.2011.05.021en
dc.identifier.urihttp://hdl.handle.net/10754/562043en
dc.description.abstractA Direct Numerical Simulation (DNS) of soot formation in an n-heptane/air turbulent nonpremixed flame has been performed to investigate unsteady strain effects on soot growth and transport. For the first time in a DNS of turbulent combustion, Polycyclic Aromatic Hydrocarbons (PAH) are included via a validated, reduced chemical mechanism. A novel statistical representation of soot aggregates based on the Hybrid Method of Moments is used [M.E. Mueller, G. Blanquart, H. Pitsch, Combust. Flame 156 (2009) 1143-1155], which allows for an accurate state-of-the-art description of soot number density, volume fraction, and morphology of the aggregates. In agreement with previous experimental studies in laminar flames, Damköhler number effects are found to be significant for PAH. Soot nucleation and growth from PAH are locally inhibited by high scalar dissipation rate, thus providing a possible explanation for the experimentally observed reduction of soot yields at increasing levels of mixing in turbulent sooting flames. Furthermore, our data indicate that soot growth models that rely on smaller hydrocarbon species such as acetylene as a proxy for large PAH molecules ignore or misrepresent the effects of turbulent mixing and hydrodynamic strain on soot formation due to differences in the species Damköhler number. Upon formation on the rich side of the flame, soot is displaced relative to curved mixture fraction iso-surfaces due to differential diffusion effects between soot and the gas-phase. Soot traveling towards the flame is oxidized, and aggregates displaced away from the flame grow primarily by condensation of PAH on the particle surface. In contrast to previous DNS studies based on simplified soot and chemistry models, surface reactions are found to contribute barely to the growth of soot, for nucleation and condensation processes occurring in the fuel stream are responsible for the most of soot mass generation. Furthermore, the morphology of the soot aggregates is found to depend on the location of soot in mixture fraction space. Aggregates having the largest primary particles populate the region closest to the location of peak soot growth. On the contrary, the aggregates with the largest number of primary particles are located much further into the fuel stream. © 2011 The Combustion Institute.en
dc.description.sponsorshipThe authors gratefully acknowledge funding from the Strategic Environmental Research and Development Program (SERDP) and the National Aeronautics and Space Administration (NASA). This research was supported in part by the National Science Foundation (NSF) through TeraGrid resources provided by the Texas Advanced Computing Center (TACC) under Grant No. TG-CTS090021. M.E.M. gratefully acknowledges support of the National Defense Science and Engineering Graduate (NDSEG) fellowship program. The authors would like to thank Dr. Pepiot-Desjardins for her help in reducing the chemical mechanism.en
dc.publisherElsevieren
dc.subjectDirect numerical simulationen
dc.subjectN-heptaneen
dc.subjectParticulate morphologyen
dc.subjectPolycyclic aromatic hydrocarbonsen
dc.subjectSooten
dc.subjectTurbulent nonpremixed combustionen
dc.titleOn the formation and early evolution of soot in turbulent nonpremixed flamesen
dc.typeArticleen
dc.contributor.departmentClean Combustion Research Centeren
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentMechanical Engineering Programen
dc.contributor.departmentReactive Flow Modeling Laboratory (RFML)en
dc.identifier.journalCombustion and Flameen
dc.contributor.institutionDepartment of Mechanical Engineering, California Institute of Technology, Pasadena, CA 91125, United Statesen
dc.contributor.institutionDepartment of Mechanical Engineering, Stanford University, Stanford, CA 94305, United Statesen
dc.contributor.institutionInstitut für Technische Verbrennung, RWTH Aachen University, 52056 Aachen, Germanyen
kaust.authorBisetti, Fabrizioen
All Items in KAUST are protected by copyright, with all rights reserved, unless otherwise indicated.