High-pressure burning velocities measurements for centrally-ignited premixed methane/air flames interacting with intense near-isotropic turbulence at constant Reynolds numbers

Chien Chia Liu, Shenqyang Steven Shy, Ming Wei Peng, Chien Wen Chiu, Yi Chih Dong

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51 Scopus citations

Abstract

This paper measures high-pressure turbulent burning velocities (S T) of lean methane spherical flames at constant turbulent Reynolds numbers (Re T≡u'L I/ν), where u' and L I are the r.m.s. turbulent fluctuation velocity and the integral length scale of turbulence and ν is the kinematic viscosity of reactants. This is achieved by adopting a recently-built double-chamber, fan-stirred cruciform burner with perforated plates that can be used to generate intense near-isotropic turbulence with negligible mean velocities while controlling the product of u'L I in proportion to the decreasing ν at elevated pressure (p) up to 1.2MPa. Results show that when Re T is fixed ranging from 6700 to 14,200, values of S T decrease similarly as laminar burning velocities (S L) with increasing p in minus exponential manners, revealing a global response of burning velocities to pressure. In general, the higher Re T, the higher S T/S L at any fixed p. It is found that the curves of S T/S L as a function of u'/S L all exhibit very strong bending under constant Re T conditions. These results not only reveal that the important effect of Re T on high-pressure S T/S L enhancement, but also suggest that recent findings related with the promotion effect of increasing pressure on S T primarily due to the enhancement of flame instabilities via the thinner flame without any discussion on the influence of Re T elevation at elevated pressure should be reconsidered. Moreover, we found that the modified values of S T at mean progress variable c̄≈0.5 show good agreements between Bunsen-type and spherical flames, suggesting that S T determined at flame surfaces with c̄=0.5 may be a better representative of itself regardless of the flame geometries. Finally, various general correlations of ST,c̄=0.5 are compared and discussed. It is found that the present scattering data under different p and Re T conditions can be merged onto a single curve of (ST,c̄=0.5-S L)/u'=0.14Da 0.47, where Da is the turbulent Damköhler number.

Original languageEnglish
Pages (from-to)2608-2619
Number of pages12
JournalCombustion and Flame
Volume159
Issue number8
DOIs
StatePublished - Aug 2012

Keywords

  • High-pressure premixed turbulent combustion
  • Intense near-isotropic turbulence
  • Turbulent burning velocities
  • Turbulent damköhler and karlovitz numbers
  • Turbulent reynolds number

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