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Three stage cool flame droplet burning behavior of n-alkane droplets at elevated pressure conditions: Hot, warm and cool flame

Published on Jan 1, 2019
· DOI :10.1016/j.proci.2018.09.015
Tanvir Farouk17
Estimated H-index: 17
(USC: University of South Carolina),
Daniel L. Dietrich13
Estimated H-index: 13
(Glenn Research Center),
Frederick L. Dryer66
Estimated H-index: 66
(Princeton University)
Cite
Abstract
Abstract Transient, isolated n -alkane droplet combustion is simulated at elevated pressure for helium-diluent substituted-air mixtures. We report the presence of unique quasi-steady, three-stage burning behavior of large sphero-symmetric n -alkane droplets at these elevated pressures and helium substituted ambient fractions. Upon initiation of reaction, hot-flame diffusive burning of large droplets is initiated that radiatively extinguishes to establish cool flame burning conditions in nitrogen/oxygen “air” at atmospheric and elevated pressures. However, at elevated pressure and moderate helium substitution for nitrogen ( X He  > 20%), the initiated cool flame burning proceeds through two distinct, quasi-steady-state, cool flame burning conditions. The classical “ Hot flame ” (∼1500 K) radiatively extinguishes into a “ Warm flame ” burning mode at a moderate maximum reaction zone temperature (∼ 970 K), followed by a transition to a lower temperature (∼765 K), quasi-steady “ Cool flame ” burning condition. The reaction zone (“flame”) temperatures are associated with distinctly different yields in intermediate reaction products within the reaction zones and surrounding near-field, and the flame-standoff ratios characterizing each burning mode progressively decrease. The presence of all three stages first appears with helium substitution near 20%, and the duration of each stage is observed to be strongly dependent on helium substitutions level between 20–60%. For helium substitution greater than 60%, the hot flame extinction is followed by only the lower temperature cool flame burning mode. In addition to the strong coupling between the diffusive loss of both energy and species and the slowly evolving degenerate branching in the low and negative temperature coefficient (NTC) kinetic regimes, the competition between the low-temperature chain branching and intermediate-temperature chain termination reactions control the “ Warm” and “ Cool ” flame quasi-steady conditions and transitioning dynamics. Experiments onboard the International Space Station with n -dodecane droplets confirm the existence of these combustion characteristics and predictions agree favorably with these observations.
  • References (13)
  • Citations (3)
Cite
References13
Newest
Published on Apr 1, 2017in Combustion and Flame 4.12
Nour Atef4
Estimated H-index: 4
(KAUST: King Abdullah University of Science and Technology),
Goutham Kukkadapu7
Estimated H-index: 7
(UConn: University of Connecticut)
+ 14 AuthorsApurba K. Das1
Estimated H-index: 1
(UConn: University of Connecticut)
The presented work was supported by Saudi Aramco under the FUELCOM program and by the King Abdullah University of Science and Technology (KAUST) with competitive research funding given to the Clean Combustion Research Center (CCRC). The work at UCONN was supported by the National Science Foundation under Grant No. CBET-1402231. The work at LLNL was supported by the U.S. Department of Energy, Vehicle Technologies Office, program managers Gurpreet Singh and Leo Breton and was performed under the a...
Published on Apr 1, 2016in Combustion and Flame 4.12
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 Self-sustaining premixed cool flames are successfully stabilized in a dimethyl ether/oxygen counterflow burner through ozone addition, creating a new platform for the quantitative measurement of cool flame extinction limits, ignition limits, and structure as well as the validation of low-temperature chemical kinetic models. First, results show that stable premixed cool flames can exist over a broad region of equivalence ratios and strain rates, which allows for the ignition and extincti...
Published on Apr 1, 2016in AIAA Journal 1.95
Vedha Nayagam13
Estimated H-index: 13
,
Daniel L. Dietrich13
Estimated H-index: 13
,
Forman A. Williams48
Estimated H-index: 48
A simplified model for droplet combustion in the partial-burning regime is applied to the cool-flame regime observed in droplet-burning experiments performed in the International Space Station with normal-alkanes fuels resulting in expressions for the quasi-steady droplet burning rate and for the flame standoff ratio. The simplified predictions are found to produce reasonable agreement with the experimentally measured values of burning-rate constants but not with their apparent dependencies on p...
Published on Mar 1, 2016in Combustion and Flame 4.12
Zhandong Wang21
Estimated H-index: 21
(KAUST: King Abdullah University of Science and Technology),
S.M. Sarathy26
Estimated H-index: 26
(KAUST: King Abdullah University of Science and Technology)
Abstract Comprehensive low-temperature oxidation mechanisms are needed to accurately predict fuel auto-ignition properties. This paper studies the effects of a previously unconsidered third O 2 addition reaction scheme on the simulated auto-ignition of n -alkanes. We demonstrate that this extended low-temperature oxidation scheme has a minor effect on the simulation of n -pentane ignition; however, its addition significantly improves the prediction of n -hexane auto-ignition under low-temperatur...
Published on Oct 1, 2015in Combustion and Flame 4.12
Yiguang Ju54
Estimated H-index: 54
(Princeton University),
Christopher B. Reuter7
Estimated H-index: 7
(Princeton University),
Sang Hee Won27
Estimated H-index: 27
(Princeton University)
Abstract 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 fla...
Published on Oct 1, 2014in Microgravity Science and Technology 1.97
Daniel L. Dietrich13
Estimated H-index: 13
(Glenn Research Center),
Vedha Nayagam4
Estimated H-index: 4
(Case Western Reserve University)
+ 9 AuthorsYu Cheng Liu10
Estimated H-index: 10
(Cornell University)
This paper summarizes the first results from isolated droplet combustion experiments performed on the International Space Station (ISS). The long durations of microgravity provided in the ISS enable the measurement of droplet and flame histories over an unprecedented range of conditions. The first experiments were with heptane and methanol as fuels, initial droplet droplet diameters between 1.5 and 5.0 m m, ambient oxygen mole fractions between 0.1 and 0.4, ambient pressures between 0.7 and 3.0 ...
Published on Jun 1, 2014in Progress in Energy and Combustion Science 26.47
W. A. Sirignano42
Estimated H-index: 42
(UCI: University of California, Irvine)
Abstract A review of research on the subject of the vaporization and burning of fuel droplets configured in a prescribed array is presented, including both classical works and research over the past decade or two. Droplet arrays and groups and the relation to sprays are discussed. The classical works are reviewed. Recent research on transient burning and vaporization of finite arrays with Stefan convection but without forced convection is presented, including extensions to non-unitary Lewis numb...
Published on Feb 1, 2014in Combustion and Flame 4.12
Tanvir Farouk17
Estimated H-index: 17
(USC: University of South Carolina),
Frederick L. Dryer66
Estimated H-index: 66
(Princeton University)
Abstract Recent experimentally observed two stage combustion of n -heptane droplets in microgravity is numerically studied. The simulations are conducted with detailed chemistry and transport in order to obtain insight into the features controlling the low temperature second stage burn. Predictions show that the second stage combustion occurs as a result of chemical kinetics associated with classical premixed “ Cool Flame ” phenomena. In contrast to the kinetic interactions responsible for premi...
Published on Dec 1, 2012in Combustion and Flame 4.12
Vedha Nayagam13
Estimated H-index: 13
,
Daniel L. Dietrich13
Estimated H-index: 13
(Glenn Research Center)
+ 2 AuthorsForman A. Williams48
Estimated H-index: 48
(UCSD: University of California, San Diego)
Abstract Experimental observations of anomalous combustion of n-heptane droplets burning in microgravity are reported. Following ignition, a relatively large n-heptane droplet first undergoes radiative extinction, that is, the visible flame ceases to exist because of radiant energy loss. But the droplet continues to experience vigorous vaporization for an extended period according to a quasi-steady droplet-burning law, ending in a secondary extinction at a finite droplet diameter, after which a ...
Published on Dec 1, 2011in Combustion and Flame 4.12
S.M. Sarathy26
Estimated H-index: 26
(LLNL: Lawrence Livermore National Laboratory),
Charles K. Westbrook62
Estimated H-index: 62
(LLNL: Lawrence Livermore National Laboratory)
+ 11 AuthorsK. Seshadri28
Estimated H-index: 28
(UCSD: University of California, San Diego)
Abstract Conventional petroleum jet and diesel fuels, as well as alternative Fischer–Tropsch (FT) fuels and hydrotreated renewable jet (HRJ) fuels, contain high molecular weight lightly branched alkanes (i.e., methylalkanes) and straight chain alkanes ( n -alkanes). Improving the combustion of these fuels in practical applications requires a fundamental understanding of large hydrocarbon combustion chemistry. This research project presents a detailed and reduced chemical kinetic mechanism for si...
Cited By3
Newest
Yiguang Ju54
Estimated H-index: 54
(Princeton University),
Christopher B. Reuter7
Estimated H-index: 7
(Princeton University)
+ -3 AuthorsSang Hee Won2
Estimated H-index: 2
(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 Flame 4.12
Mohammadhadi Hajilou2
Estimated H-index: 2
(UW: University of Wyoming),
Matthew Q. Brown (UW: University of Wyoming)+ 1 AuthorsErica Belmont5
Estimated H-index: 5
(UW: University of Wyoming)
Abstract Low temperature combustion of n-heptane was investigated through an experimental and numerical study of laminar cool flame structure and propagation speeds. Lean and stoichiometric n-heptane cool flames of equivalence ratios 0.4–1.0 were stabilized using a Hencken burner at sub-atmospheric pressures. Characterization of cool flame lift-off heights in burner-stabilized and freely propagating regimes was performed using broadband chemiluminescence and formaldehyde planar laser-induced flu...
Published on Mar 21, 2019in Combustion Theory and Modelling 1.65
Forman A. Williams48
Estimated H-index: 48
(UCSD: University of California, San Diego),
Vedha Nayagam13
Estimated H-index: 13
(Case Western Reserve University),
Vedha Nayagam4
Estimated H-index: 4
(Case Western Reserve University)
Published on Jun 27, 2019in Microgravity Science and Technology 1.97
Yang Zhang11
Estimated H-index: 11
(THU: Tsinghua University),
Xiehe Yang (THU: Tsinghua University)+ 3 AuthorsJunfu Lyu3
Estimated H-index: 3
(THU: Tsinghua University)
The unexpected finding of the quasi-steady state cool flame onboard the International Space Station motivated increasing interests to study the dynamic behaviors of cool flames. One key scientific question is how to form and stabilize a self-sustaining steady-state cool flame in a burner with well-defined boundary conditions. This paper numerically studied the stabilization of a self-sustaining steady-state premixed dimethyl ether/O2/N2 cool flame. The dual S-curve response in the perfectly-stir...