Extended flammability limits of n-heptane/air mixtures with cool flames

Liang, Wenkai; Law, Chung K.

doi:10.1016/j.combustflame.2017.06.015

Cited by 42 publications

(21 citation statements)

References 24 publications

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“…The previous study of DME premixed flame in a planar freely propagation condition also reported that the self-sustained cool flame could only exist in fuel-lean or rich regions but not in the stoichiometric condition. 16 In summary, H 2 addition exerted a pronounced effect on the structure of DME SDF, and it should be noted that H 2 addition affected cool flames much more than hot flames in terms of flame radius, reaction zone width, HRR, pollutant emissions, temperature, and so forth, which has been discussed in more details in our previous publication. 31 Here, we just make a supplementary discussion.…”

Section: Results and Discussionmentioning

confidence: 77%

“… 15 The flammability range of combustion can be extended considerably because of the cool-flame chemistry in either homogeneous or spatially diffusive combustion systems. 16 Besides, in the practical engine condition with elevated pressure and mixture preheating, the cool-flame chemical kinetics increased, and thus, its chemical timescale became comparable or even smaller than the engine combustion or turbulence timescales, which resulted in a strong interaction between the cool-flame chemistry with the engine combustion process. 17 The extremely short timescale of cool-flame chemistry will lead to an auto-ignition propagating front in the cylinder which governs the overall fuel ignition and combustion process.…”

Section: Introductionmentioning

confidence: 99%

“…The present study focuses on flammability and extinction dynamics of the DME/H 2 blended fuel using the microgravitational spherical diffusion flame (SDF) as the target physical geometry because of its pronounced advantages over the other configurations, including the counterflow flame, 7 droplet flame, 8 − 10 and freely propagating flame. 16 First, the SDF is a well-defined physical model for the burning droplet in spray flames, but it can eliminate the heat feedback from flame front to the droplet surface that would influence the fuel vaporization rate by supplying the fuel mixture into quiescent air from the spherical point source at a constant mass flux. Second, the buoyancy-free characteristics in the microgravity condition can eliminate buoyancy-driven flows, which reduces the complexity of analysis significantly.…”

Section: Introductionmentioning

confidence: 99%

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Effects of H₂ Addition on Flammability Dynamics and Extinction Physics of Dimethyl Ether in Laminar Spherical Diffusion Flame

et al. 2020

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Flame extinction is one of the most essential critical flame features in combustion because of its relevance to combustion safety, efficiency, and pollutant emissions. In this paper, detailed simulations were conducted to investigate the effect of H 2 addition on dimethyl ether spherical diffusion flame in microgravitational condition, in terms of flame structure, flammability, and extinction mechanism. The mole fraction of H 2 in the fuel mixture was varied from 0 to 15% by 5% in increment. The chemical explosive mode analysis (CEMA) method was employed to reveal the controlling physicochemical processes in extinction. The results show that the cool flame in microgravitational diffusive geometry had the “double-reaction-zone” structure which consisted of rich and lean reaction segments, while the hot flame featured the “single-reaction-zone” structure. We found that the existence of “double-reaction-zone” was responsible for the stable self-sustained cool flame because the lean zone merged with the rich zone when the cool flame was close to extinction. Additionally, the effect of H 2 addition on the cool flame was distinctively different from that of the hot flame. Both hot- and cool-flame flammability limits were significantly extended because of H 2 addition but for different reasons. Besides, for each H 2 addition case, the chemical explosive mode eigenvalues with the complex number appeared in the near-extinction zone, which implies the oscillation nature of flame in this zone which may induce extinction before the steady-state extinction turning point on the S -curve. Furthermore, as revealed by CEMA analysis, contributions of the most dominated species for extinction changed significantly with varying H 2 additions, while contributions of the key reactions for extinction at varying H 2 additions were basically identical.

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Section: Results and Discussionmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of H₂ Addition on Flammability Dynamics and Extinction Physics of Dimethyl Ether in Laminar Spherical Diffusion Flame

et al. 2020

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“…A special flow reactor design has permitted to study periodic ignition phenomena and flame propagation, thus addressing the transition from "cool" to "hot" reaction regimes [178] . For practical systems, the question arises how LT chemistry influences the combustion behavior of realistic fuels [179] under conditions where coupling between chemical reactions, transport, and heat release must be considered [180 , 181] . Ju et al [181] have recently reviewed the importance of cool flame phenomena for ignition, flame extinction, and knock, and the possibility to study LT chemistry under flame conditions.…”

Section: Selected Combustion Chemistry Advances – Overview and Recentmentioning

confidence: 99%

Combustion in the future: The importance of chemistry

Kohse‐Höinghaus

2021

Proceedings of the Combustion Institute

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Combustion involves chemical reactions that are often highly exothermic. Combustion systems utilize the energy of chemical compounds released during this reactive process for transportation, to generate electric power, or to provide heat for various applications. Chemistry and combustion are interlinked in several ways. The outcome of a combustion process in terms of its energy and material balance, regarding the delivery of useful work as well as the generation of harmful emissions, depends sensitively on the molecular nature of the respective fuel. The design of efficient, low-emission combustion processes in compliance with air quality and climate goals suggests a closer inspection of the molecular properties and reactions of conventional, bio-derived, and synthetic fuels. Information about flammability, reaction intensity, and potentially hazardous combustion by-products is important also for safety considerations. Moreover, some of the compounds that serve as fuels can assume important roles in chemical energy storage and conversion. Combustion processes can furthermore be used to synthesize materials with attractive properties. A systematic understanding of the combustion behavior thus demands chemical knowledge. Desirable information includes properties of the thermodynamic states before and after the combustion reactions and relevant details about the dynamic processes that occur during the reactive transformations from the fuel and oxidizer to the products under the given boundary conditions. Combustion systems can be described, tailored, and improved by taking chemical knowledge into account. Combining theory, experiment, model development, simulation, and a systematic analysis of uncertainties enables qualitative or even quantitative predictions for many combustion situations of practical relevance. This article can highlight only a few of the numerous investigations on chemical processes for combustion and combustion-related science and applications, with a main focus on gas-phase reaction systems. It attempts to provide a snapshot of recent progress and a guide to exciting opportunities that drive such research beyond fossil combustion.

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“…The definition of conventional flammability limit, which was based on hot flame, should be redefined due to the occurrence of cool flame. 23 Additionally, low-temperature chemistry can exhibit a typical negative temperature coefficient (NTC) behavior (i.e., fuel oxidative reactivity could be enhanced by decreasing the temperature), which was usually observed in engine knock 24 and a two-stage ignition process. 25 However, the study in ref ( 25 ) reported that the NTC phenomenon could have only occurred within a particular temperature range.…”

Section: Introductionmentioning

confidence: 99%

Comparative Study on the Dimethyl Ether Combustion Characteristics in Normal and Inverse Diffusion Spherical Flame Geometries

et al. 2020

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This paper makes a comparative study on the normal diffusion flame (NDF) and inverse diffusion flame (IDF) characteristics of dimethyl ether (DME) in microgravitational spherical diffusion flame geometry by simulations with detailed fuel chemistry and a transport model. It is found that there always existed two combustion modes (i.e., hot flame and cool flame) in either NDF or IDF condition. The combustion progress of hot flames was controlled by diffusive mixing, while that of cool flames was controlled by low-temperature competing kinetics. The cool-flame structure dynamics were far away from the chemical equilibrium. The low-temperature branching rate of DME was positively dependent on the oxygen level, while its termination rate was enhanced with the increasing temperature. Being rather distinct from the NDF counterpart, DME IDFs had the oxygen-enriched combustion feature in either hot- or cool-flame condition. Furthermore, DME hot-flame extinction was induced by thermal radiative loss, while the cool-flame extinction was induced especially by the decrease of the low-temperature branching rate. Compared with hot NDFs, it would be of less effectiveness to control the hot IDF combustion process by positive measures. However, combustion in the latter configuration was much more stable than the former. In either NDF or IDF geometry, the cool-flame chemistry could help to extend the fuel flammability range considerably, and the two-reaction-zone structure of cool flame was responsible for cool-flame stability. In addition, the IDFs had much better ignition performance than the NDF counterpart.

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Extended flammability limits of n-heptane/air mixtures with cool flames

Cited by 42 publications

References 24 publications

Effects of H₂ Addition on Flammability Dynamics and Extinction Physics of Dimethyl Ether in Laminar Spherical Diffusion Flame

Effects of H₂ Addition on Flammability Dynamics and Extinction Physics of Dimethyl Ether in Laminar Spherical Diffusion Flame

Combustion in the future: The importance of chemistry

Comparative Study on the Dimethyl Ether Combustion Characteristics in Normal and Inverse Diffusion Spherical Flame Geometries

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Extended flammability limits of n-heptane/air mixtures with cool flames

Cited by 42 publications

References 24 publications

Effects of H2 Addition on Flammability Dynamics and Extinction Physics of Dimethyl Ether in Laminar Spherical Diffusion Flame

Effects of H2 Addition on Flammability Dynamics and Extinction Physics of Dimethyl Ether in Laminar Spherical Diffusion Flame

Combustion in the future: The importance of chemistry

Comparative Study on the Dimethyl Ether Combustion Characteristics in Normal and Inverse Diffusion Spherical Flame Geometries

Contact Info

Product

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About

Effects of H₂ Addition on Flammability Dynamics and Extinction Physics of Dimethyl Ether in Laminar Spherical Diffusion Flame

Effects of H₂ Addition on Flammability Dynamics and Extinction Physics of Dimethyl Ether in Laminar Spherical Diffusion Flame