Study on stretch extinction limits of CH4/CO2 versus high temperature O2/CO2 counterflow non-premixed flames

Xing Li, Li Jia, Takakazu Onishi, Philipp Grajetzki, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa, Kaoru Maruta

Research output: Contribution to journalArticlepeer-review

33 Citations (Scopus)

Abstract

Extinction limits of counterflow non-premixed flames with normal and high temperature oxidizers were studied experimentally and numerically for development of new-type oxygen-enriched mild combustion furnace. Extinction stretch rates of CH4/CO2 (at 300K) versus O2/CO2 flames at oxygen mole fractions of 0.35 and 0.40 and oxidizer temperatures of 300K, 500K, 700K and 1000K were obtained. Investigation was also conducted for CH4/N2 (at 300K) versus air (O2/N2) flames at the same oxidizer temperatures. An effect of radiative heat loss on stretch extinction limits of oxygen-enriched flames and air flames was investigated by computations with optical thin model (OTM) and adiabatic flame model (ADI). The results show influence of radiative heat loss on stretch extinction limits was not significant in relative high fuel mole fraction regions. The extinction curve of the oxygen-enriched flames with oxygen mole fraction of 0.35 was close to that of the air flames at the oxidizer temperature of 300K. However, the extinction curve of air flames with high temperature oxidizer was comparable with that of oxygen-enriched flames with oxygen mole fraction of 0.40. Scaling analysis based on asymptotic solution of stretch extinction was applied and it was found that stretch extinction limits can be expressed by two terms. The first term is total enthalpy flux of fuel stream based on thermo-physical parameters. The second term is a kinetic term which reflects an effect of the chemical reaction rate on stretch extinction limits. OH radicals which play important roles in chain propagating and main endothermic reactions were used to represent the kinetic term of both oxygen-enriched and air flames. The global rates of OH formation in these two cases were compared to understand the contribution of kinetic term to stretch extinction limits. Variation of extinction curves of oxygen-enriched flames and air flames was well explained by the present scaling analysis. This offers an effective approach to estimate stretch extinction limits of oxygen-enriched flames based on those of air flames at the same oxidizer temperature.

Original languageEnglish
Pages (from-to)1526-1536
Number of pages11
JournalCombustion and Flame
Volume161
Issue number6
DOIs
Publication statusPublished - 2014 Jun

Keywords

  • Counterflow flame
  • Extinction limits
  • High-temperature oxygen-enriched flame
  • Non-premixed flame

ASJC Scopus subject areas

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

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