Negative pressure dependence of mass burning rates of H2/CO/O2/diluent flames at low flame temperatures

Michael P. Burke, Marcos Chaos, Frederick L. Dryer, Yiguang Ju

Research output: Contribution to journalArticle

132 Scopus citations

Abstract

Experimental measurements of burning rates, analysis of the key reactions and kinetic pathways, and modeling studies were performed for H2/CO/O2/diluent flames spanning a wide range of conditions: equivalence ratios from 0.85 to 2.5, flame temperatures from 1500 to 1800 K, pressures from 1 to 25 atm, CO fuel fractions from 0 to 0.9, and dilution concentrations of He up to 0.8, Ar up to 0.6, and CO2 up to 0.4. The experimental data show negative pressure dependence of burning rate at high pressure, low flame temperature conditions for all equivalence ratios and CO fractions as high as 0.5. Dilution with CO2 was observed to strengthen the pressure and temperature dependence compared to Ar-diluted flames of the same flame temperature. Simulations were performed to extend the experimentally studied conditions to conditions typical of gas turbine combustion in Integrated Gasification Combined Cycle processes, including preheated mixtures and other diluents such as N2 and H2O. Substantial differences are observed between literature model predictions and the experimental data as well as among model predictions themselves - up to a factor of three at high pressures. The present findings suggest the need for several rate constant modifications of reactions in the current hydrogen models and raise questions about the sufficiency of the set of hydrogen reactions in most recent hydrogen models to predict high pressure flame conditions relevant to controlling NOx emissions in gas turbine combustion. For example, the reaction O + OH + M = HO2 + M is not included in most hydrogen models but is demonstrated here to significantly impact predictions of lean high pressure flames using rates within its uncertainty limits. Further studies are required to reduce uncertainties in third body collision efficiencies for and fall-off behavior of H + O2(+M) = HO2(+M) in both pure and mixed bath gases, in rate constants for HO2 reactions with other radical species at higher temperatures, and in rate constants for reactions such as O + OH + M that become important under the present conditions in order to properly characterize the kinetics and predict global behavior of high-pressure H2 or H2/CO flames.

Original languageEnglish (US)
Pages (from-to)618-631
Number of pages14
JournalCombustion and Flame
Volume157
Issue number4
DOIs
StatePublished - Apr 1 2010

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Physics and Astronomy(all)

Keywords

  • Burning velocity
  • Flame speed
  • High pressure
  • Hydrogen
  • Kinetic mechanism
  • Low flame temperature
  • Negative reaction order
  • Syngas

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