Modeling of a swirl stabilized nHeptane flame using the CFI combustion model MAST B LIQUID

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Modeling of a swirl stabilized n-Heptane flame
using the CFI combustion modelMAST B LIQUID
Bram de Jager Jim B.W.Kok
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Contents

• Introduction
• Laminar flames with n-heptane
• Systematic reduction of chemistry
• Database creation
• Turbulent simulation
• Conclusions and recommendations

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Introduction

• MAST-B-LIQUID European Union project.
• Improvement of Mixed Air Steam Turbines cycles
  fired on liquid fuel, operated with air and steam
  injected at the compressor exit.
• Partners MLU Halle, ICEHT Patras, Demag Delaval
  Finspong, ICL London, Cyprus

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Overview LPP setup
Steam-Injector
Combustion Zone
Prevapourizing -mixing Duct
Fuel-injector
Air-Inlet
Compressor stage(s)
Turbine stage(s)
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Liquid fuel combustion model

• Maarten Luther Universität Halle
• Spray evolution.
• Spray heating and evaporisation.
• University of Twente
• Turbulent combustion.
• Fuel vapour mixing with air.

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Laminar flame simulation

• Two reaction mechanisms for n-heptane
• LLNL Curran et al 544 species and 2446
  reactions
• San Diego (SD) Williams et al 44 species and
  216 reactions
• CHEMKIN II Premix code
• Freely propagating flame at 1 atm., 400 K inlet
  temperature
• Stoichiometric mixture (F1)

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Adiabatic flame temperature
Laminar burning velocity SL(cm/s)
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Some intermediates
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CSP reduction

• Computational Singular Perturbation method (Lam
  Goussis, 1991) used for global reduction of
  reaction mechanism

0
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CSP results Steady state species
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Global CSP mechanism

• Reduction to 1 global CSP step
• O2 2 CO ? 2 CO2
• Reduction to 2 global CSP steps gives for both
  mechanisms identical steps
• O2 2 CO ? 2 CO2
• H2 CO2 ? H2O CO

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CFI-combustion model

• Composed species ?
• Reaction progress variable c
• Steady-state relations
• Element conservation

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CFI-combustion model

• defined by CSP
• Resulting system

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Database creation

• Stored in database for values of c 0,..,1
• Concentration of species
• Source terms
• Temperature
• Density
• Laminar to turbulent by integration of database
  over ß-pdf
• Solve turbulent transport equation for reaction
  progress variable (c) based on composed species

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Results 1 RPV database
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Results CO2 and source term of c
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Turbulent simulations of a premixed swirling flame
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Intermediates OH and C2H6
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Conclusions

• Similar behavior of SD and LLNL mechanisms for
  n-heptane combustion.
• Using the CSP reduced mechanism a one step
  thermochemical database is set up to simulate a
  turbulent n-heptane flame.
• Concentrations of intermediates are calculated.
• C2H6 present at flame front.

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Recommendations

• Validation of the CFI combustion model for a
  turbulent n-heptane flame with experimental data.
• Variation of the fuel/air ratios to lean
  situations.
• Introduction of steam
• Introduction of partial premixing, in order to
  simulate a realistic range of gas turbine
  conditions.
• Extension of the mechanisms with NOx chemistry
  and examination of this with CSP.

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Turbulent combustion

• n-heptane chosen as model fuel
• used as primary reference for octane rating
• cetane number equal to conventional diesel fuel
• 95 of high-quality diesel oil is an alkane
• isomers with varying number of branches (C1-C6),
  covering benzene precursors

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Reactants
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Products