Distributed Low Temperature Combustion: Fundamental Understanding of Combustion Regime Transitions
Technical Report,01 Feb 2013,31 Jul 2016
Imperial College Of Science Technology and Medicine London United Kingdom
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The objective of the current study is to bring fundamental understanding of the impact of the chemical Tauc and flow Tauf timescales on combustion regime transitions in turbulent premixed flows. Hence, Tauc is here varied via the mixture stoichiometry Phi with variations inTauf pursued in a parallel study. Aerodynamically stabilised dimethyl ether DME flames in a backstep burnt opposed jet configuration, featuring fractal generated multi-scale turbulenceRet 350, are used to study decoupled parameters affecting Tauc and combustion regime transitions from conventional flamelets into the distributed reaction zone regime. The choice of DME is partly due to the potential practical relevance, but also due to the fundamentally different chemical behaviour as compared to ethanol. The latter fuel has also been considered along with methane. Work has also been performed on the further assessment of chemical mechanisms for the considered fuels e.g. DME to establish their ability to reproduce laminar flame and auto-ignition properties. The chemical mechanisms where then used to determine parameters required in the estimation of the different Damkoehler numbers. This chemistry can be used to identify the impact of the major chemical pathways on combustion mode transitions. The conceptual multifluid approach of Spalding can be used to avoid the limitations associated with the common bimodal two-fluid description and is here explored via simultaneous OH-PLIF and PIV, permitting the identification of five separate fluid states.