TY - JOUR
T1 - On transition to cellularity in expanding spherical flames
AU - Jomaas, G.
AU - Law, C. K.
AU - Bechtold, J. K.
N1 - Funding Information:
The work at Princeton University was supported by the NASA microgravity combustion program and a block grant from BP and Ford on carbon mitigation and hydrogen economy. We thank Dr Jiao Yuan and Mr Delin Zhu for their assistance. Discussions with Professor Stephen Tse of Rutgers University about the experimental set-up were helpful, and very much appreciated.
PY - 2007
Y1 - 2007
N2 - The instant of transition to cellularity of centrally ignited, outwardly propagating spherical flames in a reactive environment of fuel-oxidizer mixture, at atmospheric and elevated pressures, was experimentally determined using high-speed schlieren imaging and subsequently interpreted on the basis of hydrodynamic and diffusional-thermal instabilities. Experimental results show that the transition Péclet number, Pec = Rc/lL, assumes an almost constant value for the near-equidiffusive acetylene flames with wide ranges in the mixture stoichiometry, oxygen concentration and pressure, where Rc is the flame radius at transition and lL the laminar flame thickness. However, for the non-equidiffusive hydrogen and propane flames, Pec respectively increases and decreases somewhat linearly with the mixture equivalence ratio. Evaluation of Pec using previous theory shows complete qualitative agreement and satisfactory quantitative agreement, demonstrating the insensitivity of Pec to all system parameters for equidiffusive mixtures, and the dominance of the Markstein number, Ze (Le - 1), in destabilization for non-equidiffusive mixtures, where Ze is the Zel'dovich number and Le the Lewis number. The importance of using locally evaluated values of lL Ze and Le, extracted from either computationally simulated one-dimensional flame structure with detailed chemistry and transport, or experimentally determined response of stretched flames, in the evaluation of Pec is emphasized.
AB - The instant of transition to cellularity of centrally ignited, outwardly propagating spherical flames in a reactive environment of fuel-oxidizer mixture, at atmospheric and elevated pressures, was experimentally determined using high-speed schlieren imaging and subsequently interpreted on the basis of hydrodynamic and diffusional-thermal instabilities. Experimental results show that the transition Péclet number, Pec = Rc/lL, assumes an almost constant value for the near-equidiffusive acetylene flames with wide ranges in the mixture stoichiometry, oxygen concentration and pressure, where Rc is the flame radius at transition and lL the laminar flame thickness. However, for the non-equidiffusive hydrogen and propane flames, Pec respectively increases and decreases somewhat linearly with the mixture equivalence ratio. Evaluation of Pec using previous theory shows complete qualitative agreement and satisfactory quantitative agreement, demonstrating the insensitivity of Pec to all system parameters for equidiffusive mixtures, and the dominance of the Markstein number, Ze (Le - 1), in destabilization for non-equidiffusive mixtures, where Ze is the Zel'dovich number and Le the Lewis number. The importance of using locally evaluated values of lL Ze and Le, extracted from either computationally simulated one-dimensional flame structure with detailed chemistry and transport, or experimentally determined response of stretched flames, in the evaluation of Pec is emphasized.
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U2 - 10.1017/S0022112007005885
DO - 10.1017/S0022112007005885
M3 - Article
AN - SCOPUS:34547484451
SN - 0022-1120
VL - 583
SP - 1
EP - 26
JO - Journal of Fluid Mechanics
JF - Journal of Fluid Mechanics
ER -