Combustion Chemistry in the Twenty-First Century: Developing a - - PowerPoint PPT Presentation

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Combustion Chemistry in the Twenty-First Century: Developing a - - PowerPoint PPT Presentation

Dec 28, 2023 138 likes •552 views

Combustion Chemistry in the Twenty-First Century: Developing a Theory-Informed Chemical Kinetic Model for the Small- Hydrocarbon Fuels James A. Miller Argonne National Laboratory Collaborators/Co-Authors/Partners Stephen Ahren Jasper

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Combustion Chemistry in the Twenty-First Century: Developing a Theory-Informed Chemical Kinetic Model for the Small- Hydrocarbon Fuels James A. Miller Argonne National Laboratory

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Collaborators/Co-Authors/Partners

  • Stephen

Klippenstein

  • Raghu

Sivaramikrishnan

  • Michael Burke

(Columbia)

  • Franklin Goldsmith

(Brown)

  • Yuri Georgievski
  • Larry Harding
  • Branko Ruscic
  • Ahren Jasper
  • Judit Zádor
  • Nils Hansen
  • Peter Glarborg
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Support

  • Argonne-Sandia High-Pressure Combustion

Consortium – DOE Office of Basic Energy Sciences

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Distinguishing Characteristics of Present Model

  • Focus on C0-C3 chemistry (plus methanol and

ethanol)– molecules large enough to exhibit low- temperature chemistry, small enough to be attacked with high-level electronic-structure methods

  • Relies heavily on theory (thermochemistry,

transport, chemical kinetics)

  • Focus on extension to high pressure
  • No fitting, no “optimization”, no adjustable

parameters

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What does “high pressure” mean?

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Thermochemistry

  • Active Thermochemical Tables
  • Very High-Level Electronic Structure Theory:

C-H-O-N species with 34 or fewer electrons – 4 (or 5) heavy atoms

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SLIDE 7

7

High Accuracy Ab Initio Thermochemistry

Central Elements

  • CCSD(T)/TZ rovibrational analysis
  • CCSD(T)/CBS(AQZ,A5Z)
  • CCSDT(Q)/DZ – CCSD(T)/DZ

Minor Corrections

  • Core-Valence

CCSD(T,full)/CBS(pcVTZ,pcVQZ)

  • Anharmonic Vibration Corrections B3LYP or MP2
  • Relativistic

CI(aug-cc-pcvtz)

  • Diagonal Born-Oppenheimer

HF/TZ 2 σ Accuracy ~ 0.2 kcal/mol Replace with CASPT2 and/or CI+QC as necessary

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SLIDE 8

Transport Properties

2 Objectives

1. Provide accurate Lennard-Jones parameters for use in flame calculations 2. Test accuracy of isotropic/Lennard-Jones potential

Methods

  • Calculate σ and ε for N2- X from “isotropically averaged

potential” using MP2/aug’dz method – use combining rules to get self parameters

  • Calculate collision integral (diffusion) “exactly” from

classical trajectories using fitted potentials

  • Calculate dipole moments and polarizabilities from high-

level electronic structure theory

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SLIDE 9

r V(r)

Lennard-Jones Potential

σ ε

12 6

( ) 4 ( ) ( )

ij ij ij

V r r r           

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H –N2 interaction

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H2 –N2 interaction

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C3H8 – N2 interaction

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Chemical Kinetics

  • RRKM/non-RRKM behavior
  • Dissociation of weakly-bound free radicals
  • Multiple-well, multiple-product-channel

problems

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Types of Chemical Reactions

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RRKM Intramolecular Dynamics

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H+O2OH+O

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Effect of non-RRKM Behavior in H+O2OH+O

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3CH2+O2→products

Courtesy of Alex Landera

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3CH2+O2 Rate Constants

Courtesy of Alex Landera

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Weakly-bound free radicals

  • Dissociate primarily to form stable molecule

and another free radical

  • Low threshold energies for dissociation

(weak bonds) with “intrinsic” potential energy barriers

  • Examples: vinyl, ethyl, n- and i-propyl (all

alkyl radicals), allyl, formyl, …

  • Not weakly bound- methyl, propargyl, …
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SLIDE 22

Timonen, et al 1987 Friedrichs ,et al 2002 Krasnoperov Helium collider

The Dissociation of Formyl Radical

Argon collider Yang, Tan, Carter, and Ju, U.S. National Meeting 2013

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HCO dissociation

tunneling Reaction threshold energy

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Yang, Tan, Carter, and Ju, U.S. National Meeting 2013

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Non-equilibrium population distributions during dissociation of weakly-bound free radicals

  • Non-equilibrium factor, fne, occurs naturally in the analytical

treatment of reversible dissociation

  • Measure of the extent to which dissociation “disturbs” the

equilibrium population distribution

  • If fne is significantly smaller than 1, get significant

disturbance ⇒ dissociation during vibrational relaxation ⇒ inadequacy of phenomenological (rate constant) description

( ) 1/ ( ) ( )

ne

x E f x E dE F E

      

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SLIDE 26

Non-Equilibrium factors for Selected Radicals

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Propyl radicals

n-C3H7 i-C3H7

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Possible Solution

  • Internal energy relaxation is presumed to be infinitely fast in

phenomenological models

  • Dissociated radical is formed before “thermalization” is

complete

  • Take dissociated radical to be formed from radical-producing

reactions, e.g. C2H6+OHC2H5+H2O C2H6+OHC2H4+H+H2O

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SLIDE 29

Reactions Investigated (or Re-Investigated) for this Project

Everything on C3H7 potential, …C3H6 …,… C3H5O…, …C2H4…,C2H5+H, C2H5+OH,C2H5+O2,C3H7+O2,C3H3 dissociation, 3CH2+O2, HCO+OH, CH2OH/CH3O dissociation,C2H3+O2, dissociation of hydroxypropyl and propoxy radicals, etc. (probably a number that I have forgotten)

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CH3+OHproducts

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CH3+OHproducts

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Comparison with Experiment

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Propane Ignition Delay Times

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Low-Temperature Autoignition of Propane

Gallagher, et al (2008)