Initiation and propagation of laminar premixed cool flames

Zhao, Peng; Liang, Wenkai; Deng, Sili; Law, Chung K.

doi:10.1016/j.fuel.2015.11.025

Cited by 92 publications

(32 citation statements)

References 37 publications

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“…Preliminary experiments that have captured some of the dynamics of ozone-assisted DME premixed cool flames can be seen in [35]. More recently, preliminary observation of DME cool flames without ozone was also reported in [36].…”

Section: Flame Regimes and Extinction Limits Of Stretched Premixed Comentioning

confidence: 95%

Numerical simulations of premixed cool flames of dimethyl ether/oxygen mixtures

Reuter

Won

2015

Combustion and Flame

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The formation and dynamics of premixed cool flames are numerically investigated by using a detailed kinetic mechanism of dimethyl ether mixtures in both freely-propagating and stretched counterflow flames with and without ozone sensitization. The present study focuses on the dynamics and transitions between cool flames and high temperature flames. The impacts of mixture temperature, inert gas temperature, and ozone concentration on low temperature ignition, cool flame formation, and flammable regions of different flame regimes are investigated. For the freely-propagating flames, three different flame structures (high temperature flames, double flames, and cool flames) are found. The present study shows that the flammability limit of dimethyl ether is significantly extended by the appearance of cool flames and that the conventional concept of the flammability limit of a high temperature flame ought to be reconsidered. Furthermore, the results demonstrate that the cool flame propagation speed can be significantly higher than that of near-limit high temperature flames and that ozone addition dramatically accelerates the formation of cool flames at low temperatures and extends the flammability limit. A schematic of a modified flammability limit diagram including both high temperature flames and cool flames is proposed. For stretched counterflow flames, the results also show that multiple flame regimes exist with and without ozone addition. It is demonstrated that at the same mixture enthalpy, ozone addition kinetically extends the cool flame extinction limit to a higher stretch rate. Moreover, with ozone addition, two different cool flame transition regimes: a low temperature ignition transition and a direct cool flame transition without an ignition limit at higher temperature, are predicted. The present results suggest that cool flames can be an important combustion process in affecting flammability limits and flame regimes as the mixture temperature, turbulent mixing, and radical production/recirculation are increased. The results also provide guidance in observing self-sustaining premixed cool flames in experiments.

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Section: Flame Regimes and Extinction Limits Of Stretched Premixed Comentioning

confidence: 95%

Numerical simulations of premixed cool flames of dimethyl ether/oxygen mixtures

Reuter

Won

2015

Combustion and Flame

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“…The main challenge in studying the dynamics of cool flames originates from the difficulty to create a stable cool flame experimentally. Efforts of previous cool flame studies have been focused on using heated surfaces and heated burners [11][12][13], jet stirred reactors [14], heated flow reactors [15,16], rapid compression machines [17], counterflow flames [5,6,[18][19][20][21], propagating flames [7,22], and droplets [3,4,23].…”

Section: Introductionmentioning

confidence: 99%

On the propagation limits and speeds of premixed cool flames at elevated pressures

2017

Combustion and Flame

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The flame speeds and propagation limits of premixed cool flames at elevated pressures are numerically modelled using dimethyl ether mixtures. The primary focus is paid on the effects of pressure, mixture dilution, computation domain, and heat loss on cool flame propagation. The results showed that cool flames exist on both fuel lean and fuel rich sides and dramatically extend the lean and rich flammability limits of conventional hot flames. There exist three different flame regimes: the hot flames, lean and rich cool flames, and double flames. A new flame flammability diagram including both cool flames and hot flames at elevated pressures is obtained. The results show that pressure significantly changes cool flame propagation and burning limits. It is found that the increase of pressure affects the propagation speeds of lean and rich cool flames differently due to the negative temperature coefficient effect. On the lean side, the increase of pressure accelerates the cool flame chemistry and shifts the transition limit of cool flame to hot flame to a lower equivalence ratio. At lower pressure, there is an extinction transition from hot flame to cool flame. However, above a critical pressure, the hot flame directly transfers to a cool flame without hot flame extinction. Moreover, increases in dilution reduce the heat release of the hot flame and promote cool flame formation. Furthermore, the results show that a smaller downstream computation domain and higher heat loss also extend the cool flame transition limit and promote cool flame formation.

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“…Firstly, combustion characteristics of DME flames are of significant practical interest as it is considered as viable alternative fuel for transportation, heating and electricity generation. Further, according to recent observations, low-temperature oxidation mode of DME can be stabilized in counter-flow at atmospheric pressure [11]. This feature enables to investigate both high-temperature combustion (HTC) and LTC regimes in the given experimental configuration.…”

Section: Computation Of Laminar Flame Structurementioning

confidence: 79%

“…Initial aim related to this device was focused on the structure and dynamics of inhibited counter-flow non-premixed flames at low and moderate strain rate, which is of practical importance in the context of fire safety science. Our latest attempts are motivated by the recent progress of numerical simulations [10] and new experimental findings [11] regarding stabilization of low-temperature combustion (LTC) regime, i.e. so called cool flames in counter-flow configuration.…”

Section: Burner Design and Setupmentioning

confidence: 99%

Experimental Apparatus and Modeling Framework for Studying Counter-Flow Laminar Flames

Nevrlý¹,

Klečka²,

Blejchař³

et al. 2019

Topical Problems of Fluid Mechanics 2019

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Laboratory scale platform suitable for investigations on the structure of laminar diffusion and premixed flames in a counter-flow burner configuration is reported within this work. In particular, it is focused on design and setup of counter-flow burner apparatus specifically aimed at stabilization of laminar premixed cool flames. One-dimensional numerical simulations of dimethyl ether-air flames with detailed chemical kinetics and multi-component transport were carried out. More complex, three-dimensional, numerical simulations were performed assuming axially symmetric flow fields in realistic burner geometry, when addressing the effect of different nozzle shape on the flow-fields and corresponding flame structure.

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Initiation and propagation of laminar premixed cool flames

Cited by 92 publications

References 37 publications

Numerical simulations of premixed cool flames of dimethyl ether/oxygen mixtures

Numerical simulations of premixed cool flames of dimethyl ether/oxygen mixtures

On the propagation limits and speeds of premixed cool flames at elevated pressures

Experimental Apparatus and Modeling Framework for Studying Counter-Flow Laminar Flames

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