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GENERATION OF SOOT BASAL STRUCTURE UNITS WITH REAXFF

13/03/2016

PhD: Michel KellerIFPEN Supervisor: Theodorus de BruinAcademic Supervisor: André Nicolle

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S U S T A I N A B L E M O B I L I T Y

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Objective:Model the chemical composition of soot particle structures in differentoperating conditions (fuel composition, thermochemical surrounding).

Use these results to investigate the chemical kinetics at the gas‐phase boundary layer and the surface sites of soot particles.

MOTIVATION

Structure                                  Kinetics

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S U S T A I N A B L E M O B I L I T Y

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METHODOLOGYObjective:Generation of a library of turbostratic soot structures spanning a wide range of fuels and engine operating conditions by molecular dynamics simulationsApproach:

We generated a gas phase precursor mixture using Chemkin.

Tested conditions:• Equivalence ratio• Temperature• Different fuels

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S U S T A I N A B L E M O B I L I T Y

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METHODOLOGYObjective:Generation of a library of turbostratic soot structures spanning a wide range of fuels and engine operating conditions by molecular dynamics simulationsApproach:

We generated a gas phase precursor mixture using Chemkin.

Tested conditions:• Equivalence ratio• Temperature• Different fuels

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S U S T A I N A B L E M O B I L I T Y

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Objective:Generation of a library of soot turbostratic structures spanning a wide range of fuels and engine operating conditions by an ReaxFF molecular dynamics simulations

METHODOLOGY

Criteria for BSUs:• aggregation of >3 molecules• distance <5.27 Å between

the centers of mass• lifetime >10ps

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Reactive Forcefield Approach* :

• Parametrization with QM calculations

Multi‐scale Approach

*as described by Chennoweth et al. (2008)

QM(6-311G**/B3LYP) and ReaxFF reaction profile for the 4 + 2 cycloaddition of O2 with butadiene, benzene, or cyclopentadiene(Cp).Published in: Kimberly Chenoweth; Adri C. T. van Duin; William A. Goddard; J. Phys. Chem. A 2008, 112, 1040-1053.

QM (6-311G**/B3LYP) and ReaxFF bond dissociation energies for C−O single, double, and triple bonds.Published in: Kimberly Chenoweth; Adri C. T. van Duin; William A. Goddard; J. Phys. Chem. A 2008, 112, 1040-1053

Motivation Multi‐scale Approach First Results

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Motivation

• CFD models correctly reproduce the Particle Size Distribution and Particle numbers, but they do not account for structural differences

• The influence of the structural differences and the functionalization of precursor molecules on the particle kinetics are not well understoodAim : Understand the influence of structural difference on the reactivityand selectivity of oxidation

Soot oxidation-induced fragmentation: Part 1: The relationship between soot nanostructure and oxidation-induced fragmentationPublished in: Hossein Ghiassi, Pal Toth, Isabel C. Jaramillo, JoAnn S. Lighty; Combustion and Flame, Volume 163, 2016, 179–187

Motivation Multi‐scale Approach First Results