TY - JOUR
T1 - Self-acceleration and global pulsation in expanding laminar H2- O2- N2 flames
AU - Huo, Jialong
AU - Saha, Abhishek
AU - Shu, Tao
AU - Ren, Zhuyin
AU - Law, Chung King
N1 - Funding Information:
The work at Tsinghua University was supported by the National Natural Science Foundation of China 91841302. The work at Princeton University was supported by the U.S. National Science Foundation (CBET, Grant No. 1827287).
Publisher Copyright:
© 2019 American Physical Society..
PY - 2019/4
Y1 - 2019/4
N2 - We report herein the quantitative data and physical insights acquired on the self-acceleration and global pulsation of spherically expanding H2-O2-N2 flames, propagating in a constant-pressure environment and subjected to hydrodynamic and diffusional-thermal instabilities over a wide range of pressures and equivalence ratios. Results show that the critical radii for the onset of the transition stage and global pulsation stage have a similar variation with pressure and equivalence ratio and can be collapsed by plotting the nondimensional values normalized by the planar flame thickness. Furthermore, through experiments with fixed flame temperature achieved by adjusting the amount of N2 in air, it is demonstrated that the global pulsation frequencies dominated by the diffusional-thermal instability increase with its intensity, which is consistent with the hypothesis that the global pulsation behavior of cellular flames arises from the continuous cell growth and splitting during the flame propagation. The global pulsation frequencies of H2-air flames, subjected to the coupled hydrodynamic and diffusional-thermal instabilities, show a nonmonotonic trend with the equivalence ratio; while their nondimensional values, normalized by the flame time, collapse and decrease with increasing equivalence ratio, in that the pressure and flame temperature effects are properly scaled out through the normalization. The acceleration exponents of the transition stage and global pulsation stage are also determined, with the latter slightly smaller than the critical value of 1.5 suggested for self-turbulization.
AB - We report herein the quantitative data and physical insights acquired on the self-acceleration and global pulsation of spherically expanding H2-O2-N2 flames, propagating in a constant-pressure environment and subjected to hydrodynamic and diffusional-thermal instabilities over a wide range of pressures and equivalence ratios. Results show that the critical radii for the onset of the transition stage and global pulsation stage have a similar variation with pressure and equivalence ratio and can be collapsed by plotting the nondimensional values normalized by the planar flame thickness. Furthermore, through experiments with fixed flame temperature achieved by adjusting the amount of N2 in air, it is demonstrated that the global pulsation frequencies dominated by the diffusional-thermal instability increase with its intensity, which is consistent with the hypothesis that the global pulsation behavior of cellular flames arises from the continuous cell growth and splitting during the flame propagation. The global pulsation frequencies of H2-air flames, subjected to the coupled hydrodynamic and diffusional-thermal instabilities, show a nonmonotonic trend with the equivalence ratio; while their nondimensional values, normalized by the flame time, collapse and decrease with increasing equivalence ratio, in that the pressure and flame temperature effects are properly scaled out through the normalization. The acceleration exponents of the transition stage and global pulsation stage are also determined, with the latter slightly smaller than the critical value of 1.5 suggested for self-turbulization.
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U2 - 10.1103/PhysRevFluids.4.043201
DO - 10.1103/PhysRevFluids.4.043201
M3 - Article
AN - SCOPUS:85065044011
SN - 2469-990X
VL - 4
JO - Physical Review Fluids
JF - Physical Review Fluids
IS - 4
M1 - 043201
ER -