Structure of tetrabrachial flames in non-premixed autoigniting dimethyl ether/air mixtures

FUEL

卷:232

Article

Jin, Tai^1,2  Wang, Xujiang¹  Luo, Kai H.¹  Luo, Kun²  Fan, Jianren² 

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

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

关键词: Two-stage ignition;    Most reactive mixture;    Tetrabrachial flames;    Direct numerical simulation;   

DOI  :  10.1016/j.fuel.2018.05.118

来源: Elsevier

【 摘 要 】

Structures of tetrabrachial flames in two-stage autoigniting dimethyl ether (DME)/air mixture under diesel engine relevant conditions are investigated by direct numerical simulation. Three cases with different initial turbulent integral length scales are studied. Results show that the first stage of autoignition initiates in lean mixtures, and subsequently develops into a diffusion-supported cool flame propagating into rich mixtures; the second-stage autoignition features spatially distributed kernels in fuel-rich mixtures, followed by hybrid auto-ignition/tetrabrachial flames. The detailed chemical structures of the tetrabrachial flames are analyzed in terms of reactant concentrations and the reaction rate profiles. The cool flame branch is dominated by low temperature reactions, while the other branches are mainly involved in high temperature oxidation of the remaining fuel and intermediate species. The excess DME is consumed in the premixed flame branches and decomposed into more stable fuels including H-2, CH4 and CO in the trailing diffusion flame, where H-2 and CO are mainly oxidized by intermediate species OH and O. The structures and reaction rates in the tetrabrachial flame exhibit significant asymmetry, which is more distinct in the mixture fraction-temperature phase space. Effects of turbulence on the timing and location of two-stage ignition are then studied. In this study, turbulence tends to advance ignition compared with laminar cases, while the first high-temperature ignition time is similar for the three cases with different initial turbulence integral length scales.

【 授权许可】

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