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Isolated n-heptane droplet combustion in microgravity: “Cool Flames” – Two-stage combustion

Published on Feb 1, 2014in Combustion and Flame 4.12
· DOI :10.1016/j.combustflame.2013.09.011
Tanvir Farouk17
Estimated H-index: 17
(USC: University of South Carolina),
Frederick L. Dryer66
Estimated H-index: 66
(Princeton University)
Cite
Abstract
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 premixed cool flame properties, those important to cool flame droplet burning are characteristically associated with the temperature range between the turnover temperature and the hot ignition. Initiation of and continuing second stage combustion involves a dynamic balance of heat generation from diffusively controlled chemical reaction and heat loss from radiation and diffusion. Within the noted temperature range, increasing reaction temperature leads to decreased chemical reaction rate and vice versa. As a result, changes of heat loss rate are dynamically balanced by heat release from chemical reaction rate as the droplet continues to burn and regress in size. At reaction temperatures below the turnover, heat loss over takes the heat release rate and extinction occurs. Should heat release exceed heat loss as the temperature increases to that for hot ignition, initiation of a high temperature burning phase may be possible. Parametric study on factors leading to initiation of the second stage burning phenomena are studied. Results show that both carbon dioxide and helium diluents can promote initiation of low temperature burning at smaller initial drop diameters than found with nitrogen as diluent. Small amounts of carbon dioxide and helium in the ambient is sufficient to activate the phenomena. The chemical kinetics dictating the second stage combustion and extinction process is also discussed.
  • References (26)
  • Citations (55)
Cite
References26
Newest
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 Oct 1, 2012in Combustion and Flame 4.12
Ruiqin Shan7
Estimated H-index: 7
(UConn: University of Connecticut),
Chun Sang Yoo18
Estimated H-index: 18
(UNIST: Ulsan National Institute of Science and Technology)
+ 1 AuthorsTianfeng Lu35
Estimated H-index: 35
(UConn: University of Connecticut)
Abstract Computational flame diagnostics (CFLDs) are systematic tools to extract important information from simulated flames, particularly when detailed chemical kinetic mechanisms are involved. The results of CFLD can be employed for various purposes, e.g. to simplify detailed chemical kinetics for more efficient flame simulations, and to explain flame behaviors associated with complex chemical kinetics. In the present study, the utility of a recently developed method of chemical explosive mode...
Published on Oct 1, 2012in Combustion and Flame 4.12
Tanvir Farouk17
Estimated H-index: 17
(Princeton University),
Frederick L. Dryer66
Estimated H-index: 66
(Princeton University)
Abstract Quasi-steady burning and extinction of droplets are of interest from both fundamental and application viewpoints. The latter is related to combustor performance and fire safety issues in reduced gravity environments. Influences of diluent in the atmosphere on isolated droplet combustion characteristics including extinction provide insights to fire extinguishment phenomena and the effectiveness of various diluents as fire suppressants. Extinction of pure methanol and methanol–water dropl...
Published on Mar 1, 2012in Combustion and Flame 4.12
Chung K. Law77
Estimated H-index: 77
(Princeton University),
Peng Zhao10
Estimated H-index: 10
(Princeton University)
Using n-heptane as the model fuel, the role of the Negative Temperature Coefficient (NTC) chemistry on ignition is computationally studied for both homogeneous mixtures and nonpremixed counterflow. For homogeneous mixtures, results show that ignition occurs in two-stages within the NTC temperature regime, with the duration and temperature increment decreasing with increasing initial temperature for the first ignition stage, leading to increased duration of the second ignition stage and thereby t...
Published on Jan 1, 2012in Combustion and Flame 4.12
Tanvir Farouk17
Estimated H-index: 17
(Princeton University),
Frederick L. Dryer66
Estimated H-index: 66
(Princeton University)
Abstract Tethered methanol droplet combustion in carbon dioxide enriched environment is simulated using a transient one-dimensional spherosymmetric droplet combustion model that includes the effects of tethering. A priori numerical predictions are compared against recent experimental data. The numerical predictions compare favorably with the experimental results and show significant effects of tethering on the experimental observations. The presence of a relatively large quartz fiber tether incr...
Published on Aug 1, 2011in Combustion Theory and Modelling 1.65
Tanvir Farouk17
Estimated H-index: 17
(Princeton University),
Frederick L. Dryer66
Estimated H-index: 66
(Princeton University)
Droplets tethering on fibers has become a well established technique for conducting droplet combustion experiments in microgravity conditions. The effects of these supporting fibers are frequently assumed to be negligible and are not considered in the experimental analysis or in numerical simulations. In this work, the effect of supporting fibers on the characteristics of microgravity droplet combustion has been investigated numerically; a priori predictions have then been compared with publishe...
Published on Jan 1, 2011
Yiguang Ju54
Estimated H-index: 54
(Princeton University),
Wenting Sun20
Estimated H-index: 20
(Princeton University)
+ 2 AuthorsZheng Chen30
Estimated H-index: 30
(PKU: Peking University)
Abstract The flame regimes of ignition and flame propagation as well as transitions between different flame regimes of n -heptane-air mixtures in a one-dimensional, cylindrical, spark assisted homogeneously charged compression ignition (HCCI) reactor are numerically modeled using a multi-timescale method with reduced kinetic mechanism. It is found that the initial mixture temperature and pressure have a dramatic impact on flame dynamics. Depending on the initial temperature gradient, there exist...
Published on Jul 1, 2010in Combustion and Flame 4.12
Wenting Sun20
Estimated H-index: 20
(Princeton University),
Zheng Chen30
Estimated H-index: 30
(PKU: Peking University)
+ 1 AuthorsYiguang Ju54
Estimated H-index: 54
(Princeton University)
A direct path flux analysis (PFA) method for kinetic mechanism reduction is proposed and validated by using high temperature ignition, perfect stirred reactors, and steady and unsteady flame propagations of n-heptane and n-decane/air mixtures. The formation and consumption fluxes of each species at multiple reaction path generations are analyzed and used to identify the important reaction pathways and the associated species. The formation and consumption path fluxes used in this method retain fl...
Published on Jul 1, 2007in International Journal of Chemical Kinetics 1.42
Marcos Chaos22
Estimated H-index: 22
(Princeton University),
Andrei F. Kazakov24
Estimated H-index: 24
(Princeton University)
+ 1 AuthorsFrederick L. Dryer66
Estimated H-index: 66
(Princeton University)
A chemical kinetic mechanism has been developed to describe the high-temperature oxidation and pyrolysis of n-heptane, iso-octane, and their mixtures. An approach previously developed by this laboratory was used here to partially reduce the mechanism while maintaining a desired level of detailed reaction information. The relevant mechanism involves 107 species undergoing 723 reactions and has been validated against an extensive set of experimental data gathered from the literature that includes ...
Published on Oct 1, 2006in Combustion and Flame 4.12
Michael R Foster2
Estimated H-index: 2
(Drexel University),
Howard Pearlman6
Estimated H-index: 6
(Drexel University)
Abstract Natural convection plays an important role in all terrestrial, Lunar, and Martian-based, unstirred, static reactor cool flame and low-temperature autoignitions, since the Rayleigh number (Ra) associated with the self-heating of the reaction exceeds the critical Ra (approximately 600) for onset of convection. At near-zero gravity, Ra g ; Martian, 0.38 g ; Lunar, 0.16 g ; and reduced gravity, ∼ 10 −2 g ). Representative results show the evolution of the visible light emission using an equ...
Cited By55
Newest
Published in Combustion and Flame 4.12
Alex G. Novoselov (Princeton University), Christopher B. Reuter7
Estimated H-index: 7
(Princeton University)
+ -3 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 ...
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...
Published on Mar 1, 2019in Fuel Processing Technology 4.51
Jie Chen (Chongqing University), Yinhu Kang9
Estimated H-index: 9
(Chongqing University)
+ 7 AuthorsLin Mei3
Estimated H-index: 3
Abstract The near-extinction oscillatory dynamics and underlying mechanism of the dimethyl ether (DME) spherical diffusion flames in the hot- and cool-flame conditions were studied by the numerical approach with detailed chemistry and transport models. It was found that the self-sustaining spherical cool diffusion flame could be readily obtained in a wide range of parameters, and additionally, the flammability limit could be considerably extended by the cool-flame chemistry. Strong oscillations ...
Published on Mar 1, 2019in International Journal of Heat and Mass Transfer 4.35
A.E. Saufi (Leonardo), Alessio Frassoldati34
Estimated H-index: 34
(Leonardo)
+ 1 AuthorsAlberto Cuoci27
Estimated H-index: 27
(Leonardo)
Abstract This paper aims at presenting the DropletSMOKE++ solver, a comprehensive multidimensional computational framework for the evaporation of fuel droplets, under the influence of a gravity field and an external fluid flow. The Volume Of Fluid (VOF) methodology is adopted to dynamically track the interface, coupled with the solution of energy and species equations. The evaporation rate is directly evaluated based on the vapor concentration gradient at the phase boundary, with no need of semi...
Published on Feb 1, 2019in Acta Astronautica 2.48
V. V. Tyurenkova8
Estimated H-index: 8
(RAS: Russian Academy of Sciences),
V.V. Tyurenkova (RAS: Russian Academy of Sciences)
Abstract This paper is devoted to the burning of an isolated n-heptane droplet in microgravity and analysis of the experimental data presented by FLEX experiment. Developing the classical analytical research methodology, proposed by Forman A. Williams, and using our obtained analytical solutions for the problem of droplet equilibrium evaporation and combustion, the analytical solutions to solve the problem of two regimes of droplet burning were found. To explain the presence of the radiative fla...
Published on Jan 22, 2019
Ahmad Kazemi Fard (TMU: Tarbiat Modares University), Hassan Khaleghi5
Estimated H-index: 5
(TMU: Tarbiat Modares University),
Reza Ebrahimi12
Estimated H-index: 12
(KNTU: K.N.Toosi University of Technology)
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 ...