Effects of pressure and Karlovitz number on the turbulence-flame interactions in lean premixed H2/air flames

FUEL

卷:234

Article

Wang, Xujiang¹  Jin, Tai^1,2  Xie, Yongliang³  Luo, Kai H.¹ 

[1] UCL, Dept Mech Engn, London WC1E 7JE, England

[2] Zhejiang Univ, State Key Lab Clean Energy Utilizat, Hangzhou 310027, Zhejiang, Peoples R China

[3] Southwest Jiaotong Univ, Sch Mech Engn, Chengdu 610031, Sichuan, Peoples R China

关键词: Premixed turbulent flame;    Elevated pressure;    Turbulence intensity;    Flame front structure;    Chemical pathway;   

DOI  :  10.1016/j.fuel.2018.07.158

来源: Elsevier

【 摘 要 】

This paper presents three-dimensional direct numerical simulations of lean premixed turbulent H-2/air flames in the thin and distributed reaction zones, with the Karlovitz numbers at 60, 110, 150 and 1000, and pressures at 1 and 5 atm, respectively. Flame front structures and chemical pathways are examined in detail to investigate the effects of pressure and turbulence on flames. There is an increasing number of finer structures on the flame front with increased Karlovitz number. Eddy structures are observed downstream of the reaction zone under high turbulence intensity and thus Karlovitz number, indicating that the turbulent eddies are small and energetic enough to break through the distributed reaction zone. Statistical analysis indicates that the probability of high curvatures increases with increasing Karlovitz number at a constant pressure. When the Karlovitz number is kept constant, the probability of high curvatures is significantly higher at the atmospheric pressure than at elevated pressure. The approximation of Schmidt number (Sc = 1) in theoretical analysis introduces errors in the estimation of the smallest flow scale and the Karlovitz number. Accordingly, in the turbulent flame regime diagram, the boundary between the thin reaction zone and the distributed reaction zone should be modified at the elevated pressure. Moreover, the decorrelation of heat release and H-2 consumption is directly related to turbulence intensity, and the decorrelation is reduced at the elevated pressure. Due to the enhanced radical transport at high Karlovitz number, chemical pathways can be locally changed, which is more significant at elevated pressure.

【 授权许可】

Free