Ignition transition in turbulent premixed combustion

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Title:	Ignition transition in turbulent premixed combustion
Authors:	Shy,SS;Liu,CC;Shih,WT
Contributors:	機械工程學系
Date:	2010
Issue Date:	2012-03-27 17:03:24 (UTC+8)
Publisher:	國立中央大學
Abstract:	Recently, Shy and his co-workers reported a turbulent ignition transition based on measurements of minimum ignition energies (MIE) of lean premixed turbulent methane combustion in a centrally-ignited, fan-stirred cruciform burner capable of generating intense isotropic turbulence. Using the same methodology, this paper presents new complete MIE data sets for stoichiometric and rich cases at three different equivalence ratios phi = 1.0, 1.2 and 1.3, each covering a wide range of a turbulent Karlovitz number (Ka) indicating a time ratio between chemical reaction and turbulence. Thus, ignition transition in premixed turbulent combustion depending on both Ka and phi can be identified for the first time. It is found that there are two distinct modes on ignition in randomly stirred methane-air mixtures (ignition transition) separated by a critical Ka where values of Ka(c) approximate to 8-26 depending on phi with the minimum Ka(c) occurring near phi = 1. For Ka < Ka(c). MIE increases gradually with Ka, flame kernel formation is similar to laminar ignition remaining a torus, and 2D laser tomography images Of Subsequent outwardly-propagating turbulent flames show sharp fronts. For Ka > Ka(c), MIE increases abruptly with Ka, flame kernel is disrupted, and subsequent randomly-propagating turbulent flames reveal distributed-like fronts. Moreover, we introduce a reaction zone Peclet number (P(RZ)) indicating the diffusivity ratio between turbulence and chemical reaction, such that the aforementioned very scattering MIE data depending on Ka and phi can be collapsed into a single curve having two drastically different increasing slopes with P(RZ) which are separated by a critical P(RZ) approximate to 4.5 showing ignition transition. Finally, a physical model is proposed to explain these results. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Relation:	COMBUSTION AND FLAME
Appears in Collections:	[Departmant of Mechanical Engineering ] journal & Dissertation

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