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

Jin, T; Wang, X; Luo, KH; Luo, K; Fan, J; (2018) Structure of tetrabrachial flames in non-premixed autoigniting dimethyl ether/air mixtures. Fuel , 232 pp. 90-98. 10.1016/j.fuel.2018.05.118. Green open access

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Abstract

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 autoignition/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 , CH 4 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.

Type: Article
Title: Structure of tetrabrachial flames in non-premixed autoigniting dimethyl ether/air mixtures
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.fuel.2018.05.118
Publisher version: http://doi.org/10.1016/j.fuel.2018.05.118
Language: English
Additional information: Copyright © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).
Keywords: Two-stage ignition, Most reactive mixture, Tetrabrachial flames, Direct numerical simulation
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering
URI: http://discovery.ucl.ac.uk/id/eprint/10050480
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