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Low-temperature multistage warm diffusion flames

Published on Sep 1, 2018in Combustion and Flame4.12
· DOI :10.1016/j.combustflame.2018.03.013
Omar R. Yehia2
Estimated H-index: 2
(Princeton University),
Christopher B. Reuter7
Estimated H-index: 7
(Princeton University),
Yiguang Ju54
Estimated H-index: 54
(Princeton University)
Cite
Abstract
Abstract We report on experimental evidence of the existence of a new self-sustaining low-temperature multistage warm diffusion flame, existing between the cool flame and hot flame, at atmospheric pressure in the counterflow geometry. The structure of multistage warm diffusion flames was examined by using thermometry, laser-induced fluorescence, and chemiluminescence measurements. It was found that the warm diffusion flame has a two-staged double flame structure, with a leading diffusion cool flame stage on the fuel side and a second intermediate stage on the oxidizer side, with strong heat release in the second stage that can be comparable to that of the first stage. The results demonstrate that the spatially-distinct multistage character is due to the low-temperature fuel reactivity that allows for the production of reactive intermediates in a leading cool flame. These intermediates are then oxidized, on the oxidizer side, in a second stage via intermediate-temperature chemistry. In the case of dibutyl ether, the low-temperature peroxy branching pathway supports the first cool flame oxidation stage and produces intermediates such as alkyl and carbonyl radicals. The alkyl and carbonyl radicals then react with the hydroperoxyl radical and molecular oxygen to form the second oxidation stage. A detailed analysis revealed that ozone addition in the oxidizer promotes the second stage oxidation by increasing both the radical pool population and the flame temperature, but does not fundamentally change the multistage flame structure. Furthermore, the analysis revealed that with the increase of fuel concentration, a single-stage cool flame can ignite to a warm flame or a hot flame. Moreover, a warm flame can extinguish into a cool flame or ignite to a hot flame when the fuel concentration is substantially reduced or increased, respectively. Finally, under certain conditions, a hot flame can extinguish directly into either a warm flame or a cool flame. Hence, the results suggest that the multistage warm flame can act as a critical bridge between cool flames and hot flames and that it is a fundamental burning mode characteristic of low-temperature non-premixed combustion. The multistage warm diffusion flame is particularly relevant to combustion in highly turbulent flow fields and in microgravity environments, owing to the possibility of long residence times.
  • References (54)
  • Citations (2)
Cite
References54
Newest
Published on Nov 1, 2017in Combustion and Flame4.12
Sébastien Thion6
Estimated H-index: 6
(University of Orléans),
Casimir Togbé25
Estimated H-index: 25
(CNRS: Centre national de la recherche scientifique)
+ 2 AuthorsPhilippe Dagaut50
Estimated H-index: 50
(CNRS: Centre national de la recherche scientifique)
Abstract The oxidation of dibutyl-ether, a potential lignocellulosic biofuel was studied in a jet-stirred reactor. Fuel-lean, stoichiometric and fuel-rich mixtures were oxidized at a constant fuel mole fraction (1000 ppm), at temperatures ranging from 470 to 1250 K, pressures of 1 and 10 atm, and constant residence time (70 and 700 ms, respectively). The mole fraction profiles obtained through sonic probe sampling, gas chromatography and Fourier transform infrared spectrometry were used to devel...
Published on Jul 4, 2017in Combustion Theory and Modelling1.65
Vedha Nayagam4
Estimated H-index: 4
(Case Western Reserve University),
Daniel L. Dietrich13
Estimated H-index: 13
(Glenn Research Center),
Forman A. Williams48
Estimated H-index: 48
(UCSD: University of California, San Diego)
A Burke–Schumann description of three different regimes of combustion of a fuel droplet in an oxidising atmosphere, namely the premixed-flame regime, the partial-burning regime and the diffusion-flame regime, is presented by treating the fuel and oxygen leakage fractions through the flame as known parameters. The analysis shows that the burning-rate constant, the flame-standoff ratio, and the flame temperature in these regimes can be obtained from the classical droplet-burning results by suitabl...
Published on May 1, 2017in Combustion and Flame4.12
Christopher B. Reuter7
Estimated H-index: 7
(Princeton University),
Minhyeok Lee2
Estimated H-index: 2
(Princeton University)
+ 1 AuthorsYiguang Ju54
Estimated H-index: 54
(Princeton University)
Abstract The low-temperature oxidation of hydrocarbon fuels has received increasing attention as advanced engines seek to operate in less conventional combustion regimes. Large n -alkanes are a notable component of many real transportation fuels and possess strong reactivity in this important low-temperature range. These n -alkanes have been studied extensively in various canonical kinetic experiments but seldom in systems with strong coupling between low-temperature chemistry, transport, and he...
Published on Apr 1, 2017in Combustion and Flame4.12
Yiguang Ju54
Estimated H-index: 54
(Princeton University)
Abstract The flame speeds and propagation limits of premixed cool flames at elevated pressures are numerically modeled 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 ...
Published on Mar 16, 2017in Energy & Fuels3.02
Takashige Shimizu1
Estimated H-index: 1
,
Hisasi Nakamura48
Estimated H-index: 48
+ 2 AuthorsKaoru Maruta34
Estimated H-index: 34
Laser-induced fluorescence (LIF) measurements were applied for the first time to a micro flow reactor with a controlled temperature profile to investigate general combustion and ignition characteristics of hydrogen (H2/O2/N2 mixture at O2/N2 = 1:9), methane, n-butane, and dimethyl ether (DME) (fuel/air mixtures). For the hydrogen case, overall flame responses of the H2/O2/N2 mixture against inlet flow velocity were investigated on the basis of the OH-LIF measurement. The existence of the three k...
Published on Feb 1, 2017in Combustion and Flame4.12
Sili Deng6
Estimated H-index: 6
(Princeton University),
Dong Han11
Estimated H-index: 11
(Princeton University),
Chung K. Law77
Estimated H-index: 77
(Princeton University)
Abstract Cool flames, governed by low-temperature chemistry, are closely related to engine knock. Since the low-temperature chemical kinetics is promoted at elevated pressures, the ignition and extinction of nonpremixed cool flame at elevated pressures were experimentally and computationally investigated herein in the counterflow. Specifically, the hysteretic ignition and extinction behavior of the nonpremixed cool flame was for the first time observed and quantified. S-curve analysis was conduc...
Published on Jan 9, 2017
Yiguang Ju54
Estimated H-index: 54
,
Eric Lin1
Estimated H-index: 1
,
Christopher B. Reuter7
Estimated H-index: 7
Published on Jan 1, 2017
Christopher B. Reuter7
Estimated H-index: 7
(Princeton University),
Sang Hee Won27
Estimated H-index: 27
(Princeton University),
Yiguang Ju54
Estimated H-index: 54
(Princeton University)
Abstract Due to their natural coupling of low-temperature chemistry and transport, cool flames are a valuable platform for drawing fundamental understandings of complicated phenomena relevant to real engines. In this study, self-sustaining partially premixed cool flames of dimethyl ether are investigated in detail through the use of an ozone-assisted counterflow burner. A double cool flame with distinct diffusion flame and premixed flames sides is visibly observed at increased fuel loading and e...
Published on Jan 1, 2017
Chae Hoon Sohn14
Estimated H-index: 14
(Sejong University),
Hee Sun Han1
Estimated H-index: 1
(Sejong University)
+ 2 AuthorsSang Hee Won27
Estimated H-index: 27
(Princeton University)
Abstract The dynamics of near-limit cool diffusion flames are investigated experimentally and numerically by studying transient flame evolution and instability. In order to observe the effects of chemistry-transport coupling on ignition and instability in a cool diffusion flame, diffusion flames of n-heptane and pure oxygen are sensitized by ozone in a counterflow burner. First, it is found from experimental observations that the immediate addition of ozone to the oxidizer side of a frozen flow ...
Published on Jan 1, 2017
Viswanath R. Katta25
Estimated H-index: 25
,
William M. Roquemore16
Estimated H-index: 16
(FFO: Wright-Patterson Air Force Base)
Abstract Low-temperature (∼700 K) “cool” flames formed with n-heptane fuel were observed in the experiments conducted under microgravity. Recently, Won et al. demonstrated experimentally that such “cool” flames could be established under normal gravity. However, as ozone was added to air for supporting the flames in that experiment, the fundamental question on the formation of a self-supported n-heptane/air “cool” flame remained unanswered. A numerical investigation is conducted for (1) finding ...
Cited By2
Newest
Published on 2019in Combustion and Flame4.12
Alex G. Novoselov (Princeton University), Christopher B. Reuter7
Estimated H-index: 7
(Princeton University)
+ 6 AuthorsMichael E. Mueller15
Estimated H-index: 15
(Princeton University)
Abstract Turbulence, low-temperature chemistry, and their interactions in the form of turbulent cool flames are critical to understanding and improving advanced engines. Design of such engines requires tractable simulations which in turn necessitate turbulent combustion models that can account for cool flames. While manifold-based turbulent combustion models are an attractive option for hot flames, their applicability to cool flames is not yet fully understood. This is partially due to the lack ...
Published on 2019in Progress in Energy and Combustion Science26.47
Yiguang Ju54
Estimated H-index: 54
(Princeton University),
Christopher B. Reuter7
Estimated H-index: 7
(Princeton University)
+ 2 AuthorsSang Hee Won3
Estimated H-index: 3
(USC: University of South Carolina)
Abstract Cool flames play a critical role in ignition timing, burning rate, burning limits, engine knocking, and emissions in conventional and advanced combustion engines. This paper provides an overview of the recent progress in experimental and computational studies of cool flames. First, a brief review of low-temperature chemistry and classical studies of cool flames is presented. Next, the recent experimental and computational findings of cool flames in microchannels, microgravity droplet co...
Published on Oct 1, 2019in Combustion and Flame4.12
Omar R. Yehia2
Estimated H-index: 2
(Princeton University),
Christopher B. Reuter7
Estimated H-index: 7
(Princeton University),
Yiguang Ju54
Estimated H-index: 54
(Princeton University)
Abstract The development of alternative drop-in fuels and fuel blends with petroleum-derived fuels necessitate an understanding of the kinetic interactions between aromatics and alkanes for the development of advanced low-temperature combustion engines. In the present study, the role of aromatic chemistry on n -alkane low-temperature chemistry is investigated by using nitrogen-diluted nonpremixed cool flames of n -dodecane/ n -propylbenzene blends in an atmospheric counterflow burner. Effects of...
Published on Jan 1, 2019
Omar R. Yehia2
Estimated H-index: 2
(Princeton University),
Christopher B. Reuter7
Estimated H-index: 7
(Princeton University),
Yiguang Ju54
Estimated H-index: 54
(Princeton University)
Abstract We demonstrate experimentally, perhaps for the first time, the existence of low-temperature multistage diffusion flames of n -alkanes. Multistage diffusion flames of n -heptane, n -decane, and n -dodecane are established in an atmospheric counterflow burner. Planar laser-induced fluorescence, chemiluminescence, and thermometry are used to probe the structures of such flames. In the first flame zone, the majority of the fuel is partially oxidized via low-temperature peroxy chemistry. In ...
Published on Jan 1, 2019
Eric Lin1
Estimated H-index: 1
(Princeton University),
Christopher B. Reuter7
Estimated H-index: 7
(Princeton University),
Yiguang Ju54
Estimated H-index: 54
(Princeton University)
Abstract The near-limit diffusion flame regimes and extinction limits of dimethyl ether at elevated pressures and temperatures are examined numerically in the counterflow geometry with and without radiation at different oxygen concentrations. It is found that there are three different flame regimes—hot flame, warm flame, and cool flame—which exist, respectively, at high, intermediate, and low temperatures. Furthermore, they are governed by three distinct chain-branching reaction pathways. The re...
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