کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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4764496 | 1423550 | 2018 | 9 صفحه PDF | دانلود رایگان |
This paper measures turbulent spark ignition probability and minimum ignition energy (MIE) of the pre-vaporized iso-octane/air mixture at an equivalence ratio Ï = 0.8 at 373 K with Le â 2.98 over a wide range of turbulent intensities (uâ²/SL), where Le is the mixture's effective Lewis number and SL 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 MIET/MIEL = Ð versus uâ²/SL change drastically from linearly to exponentially when uâ²/SL is greater than a critical value of 4.8, which is much smaller than previous rich methane data (Le > 1) at Ï = 1.2 with (uâ²/SL)c â 16 and at Ï = 1.3 with (uâ²/SL)c â 24, revealing MIE transition. The subscripts T and L represent turbulent and laminar properties. When a reaction zone Péclet number PeRZ =uâ²Î·k/αRZ 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 Ð1 = 1 + 0.4PeRZ in the pre-transition and Ð2 â¼ PeRZ4 in the post-transition with the transition occurring at (PeRZ)c â 4.2, showing similarity on MIE transition. ηk is the Kolmogorov length scale of turbulence and αRZ is the reaction zone thermal diffusivity estimated at the instant of kernel formation.
Journal: Combustion and Flame - Volume 187, January 2018, Pages 87-95