Fluidynamics and kinetics aspects of hydrogen combustion

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Fluidynamics and kinetics aspects of hydrogen
combustion
A. Frassoldati,T. Faravelli, E. Ranzi
Dipartimento di Chimica, Materiali e Ingegneria
Chimica, Politecnico di Milano, ITALY
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Revision of the H2/O2 Mechanism
Hierarchy and Modularity are the relevant
properties of the kinetic schemes H2/O2 is the
first sub-mechanism for the modeling of larger
fuels
Chemistry of NOx and Nitrogen compounds was
recently revised Faravelli, T., Frassoldati, A.,
Ranzi, E., Comb Flame, 132188 (2003)
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NEW VALIDATION OF THE H2 MECHANISM
The mechanism has been compared with experimental
data in a very wide range of conditions
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H2 FLAME SPEED Diluent Effect
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H2 FLAME SPEED Pressure Effect (1-20 atm)
Revised Mechanism improves predictions at high
pressure

• Prediction improved at high pressure due to
  re-evaluation of reaction
• H OH M H2O M

Tse, S.D., Zhu,D.L., Law,C.K., Proc. Comb. Inst.,
281793 (2000).
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H2 - NOx SYSTEMS COUNTERFLOW FLAMES
Air
H2X N2100-X

• Dilution with N2 reduces Temperature and Thermal
  NOx formation

Rørtveit, G.J. Hustad, J.E. Li, S.C. Williams,
F.A., Comb Flame 13048 (2002).
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H2 - NOx SYSTEMS IGNITION DELAY TIMES
Stoichiometric H2/Air mixture at P2 atm effect
of NO addition
The effect is mainly due to the reaction NO
HO2 NO2 OH which converts HO2 into more
reactive OH radicals
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H2 - NOx SYSTEMS IGNITION DELAY TIMES
Stoichiometric H2/Air mixture effect of
Pressure and 3.56 NO2 addition
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NOx predictions in H2 TURBULENT FLAMES Sandia
hydrogen jet Flame 14,000 cells
T (K)

• Fluent 6.1
• 2D-axisymmetric grid of 14,000 cells
• Modified1 k-e model
• composition PDF transport model
• Hydrogen Detailed kinetic mechanism

http//www.ca.sandia.gov/tdf/Workshop.html
1Hossain M., Jones J.C., Malalasekera W., Flow,
Turb. and Combustion, 67217 (2001).
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TURBULENT FLAMES Sandia H2 Jet FlameFrom CFD
computations a proper Post-Processor predicts
NOx with detailed kinetics
http//www.ca.sandia.gov/TNF/DataArch/H2HeData.htm
l
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CONCLUSIONS

• Revision of a detailed H2/O2 kinetic mechanism
• on the basis of recent kinetic and thermodynamic
  data.
• Validation against a wide range of experimental
  conditions
• Good agreement also when considering NOx
  chemistry
• and interactions.
• Detailed chemistry is also successfully applied
  to turbulent flames