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Số người truy cập: 107,040,545

 Spark ignition probability and minimum ignition energy transition of the lean iso-octane/air mixture in premixed turbulent combustion
Tác giả hoặc Nhóm tác giả: L.J. Jiang, S. Shy, M.T. Nguyen, S.Y. Huang, D.W. Yu
Nơi đăng: Combustion and Flame; Số: 187;Từ->đến trang: 87-95;Năm: 2018
Lĩnh vực: Khoa học; Loại: Bài báo khoa học; Thể loại: Quốc tế
TÓM TẮT
ABSTRACT
This paper measures turbulent spark ignition probability and minimum ignition energy (MIE) of the prevaporized iso-octane/air mixture at an equivalence ratio φ = 0.8 at 373 K with Le ≈ 2.98 over a wide range of turbulent intensities ( u'/S_L ), where Le is the mixture’s effective Lewis number and S_L is the laminar burning velocity. Ignition experiments using a fixed 2-mm electrode gap are conducted in a large dual-chamber, constant-temperature/pressure, fan-stirred 3D cruciform burner capable of generating near-isotropic turbulence. Spark discharges having nearly square voltage and current waveforms are created for accurate determination of the ignition energy ( Eig ) across the electrodes. MIE ≡ Eig(50%) that is determined statistically from many repeated experiments at a given condition using a range of Eig to identify an overlapping energy band within which ignition and non-ignition coexist even at the “same discharge Eig ”, where the subscript “ig(50%)” indicates 50% ignitability. Results show that the increasing slopes of MIE_T /MIE L = Г versus u'/S_L change drastically from linearly to exponentially when u'/S_L is greater than a critical value of 4.8, which is much smaller than previous rich methane data ( Le > 1) at φ = 1.2 with ( u'/S_L )c ≈ 16 and at φ = 1.3 with ( u'/S_L )c ≈ 24, revealing MIE transition. The subscripts T and L represent turbulent and laminar properties. When a reaction zone Péclet number Pe_RZ = u'η_k /α_RZ is used for scaling, it is found that both present lean iso-octane and previous methane data can be collapsed onto a general correlation of Г1 = 1 + 0.4 Pe_RZ in the pre-transition and Г2 ∼ (Pe_RZ)^4 in the post-transition with the transition occurring at ( Pe_RZ ) c ≈ 4.2, showing similarity on MIE transition. η_k is the Kolmogorov length scale of turbulence and α_RZ is the reaction zone thermal diffusivity estimated at the instant of kernel formation.
[ jiang-2018-spark ignition probability and mini.pdf ]
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