Ignition of uniform droplet-laden weakly turbulent flows following a laser spark.
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| Title: | Ignition of uniform droplet-laden weakly turbulent flows following a laser spark. |
|---|---|
| Authors: | de Oliveira, Pedro M.1 pm580@cam.ac.uk, Allison, Patton M.1, Mastorakos, Epaminondas1 |
| Source: | Combustion & Flame. Jan2019, Vol. 199, p387-400. 14p. |
| Subjects: | Turbulent flow, Laser beams, Mixtures, Turbulence, Wavenumber |
| Abstract: | Abstract The forced ignition process has a stochastic nature, which can be intensified due to turbulence and mixture fluctuations. Although fuel droplets represent strong inhomogeneities which are generally detrimental to ignition, the presence of small droplets has been found to enhance flame speeds, decrease minimum ignition energy, and improve the ignitability of overall lean mixtures. In order to understand which factors are conducive to ignition of sprays, a spherically expanding flame is investigated, which is produced by a laser spark in a uniform dispersion of ethanol droplets in turbulent air. The flame is visualised by schlieren and OH*-chemiluminescence for overall equivalence ratios of 0.8–2, Sauter mean diameter of approximately 25 μ m, and u ′/ S L ranging from 0.9 to 1.3, where u ′ and S L denote the rms axial velocity and laminar burning velocity, respectively. The timescales of the spark's effects on the flame are measured, as well as quenching timescales and initial kernel sizes conditional on ignition or failure. Small kernels quenched faster than approximately 0.6 ms, that is, the duration of the flame overdrive, and a minimum kernel radius for ignition of 1 mm was observed. The short-mode of ignition failure was suppressed by increasing the laser energy and, consequently, the initial kernel size. Nevertheless, the ignitability of lean mixtures was only effectively improved through high-energy sparks and partial prevaporisation of the fuel. Virtually all kernels ignited once prevaporisation was increased, and the gas-phase equivalence ratio was approximately 75% of the lower flammability limit, with ignition being limited only by laser breakdown. [ABSTRACT FROM AUTHOR] |
| Copyright of Combustion & Flame is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | Engineering Source |
| FullText | Text: Availability: 0 |
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| Header | DbId: egs DbLabel: Engineering Source An: 133750413 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: Ignition of uniform droplet-laden weakly turbulent flows following a laser spark. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22de+Oliveira%2C+Pedro+M%2E%22">de Oliveira, Pedro M.</searchLink><relatesTo>1</relatesTo><i> pm580@cam.ac.uk</i><br /><searchLink fieldCode="AR" term="%22Allison%2C+Patton+M%2E%22">Allison, Patton M.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Mastorakos%2C+Epaminondas%22">Mastorakos, Epaminondas</searchLink><relatesTo>1</relatesTo> – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Combustion+%26+Flame%22">Combustion & Flame</searchLink>. Jan2019, Vol. 199, p387-400. 14p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Turbulent+flow%22">Turbulent flow</searchLink><br /><searchLink fieldCode="DE" term="%22Laser+beams%22">Laser beams</searchLink><br /><searchLink fieldCode="DE" term="%22Mixtures%22">Mixtures</searchLink><br /><searchLink fieldCode="DE" term="%22Turbulence%22">Turbulence</searchLink><br /><searchLink fieldCode="DE" term="%22Wavenumber%22">Wavenumber</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: Abstract The forced ignition process has a stochastic nature, which can be intensified due to turbulence and mixture fluctuations. Although fuel droplets represent strong inhomogeneities which are generally detrimental to ignition, the presence of small droplets has been found to enhance flame speeds, decrease minimum ignition energy, and improve the ignitability of overall lean mixtures. In order to understand which factors are conducive to ignition of sprays, a spherically expanding flame is investigated, which is produced by a laser spark in a uniform dispersion of ethanol droplets in turbulent air. The flame is visualised by schlieren and OH*-chemiluminescence for overall equivalence ratios of 0.8–2, Sauter mean diameter of approximately 25 μ m, and u ′/ S L ranging from 0.9 to 1.3, where u ′ and S L denote the rms axial velocity and laminar burning velocity, respectively. The timescales of the spark's effects on the flame are measured, as well as quenching timescales and initial kernel sizes conditional on ignition or failure. Small kernels quenched faster than approximately 0.6 ms, that is, the duration of the flame overdrive, and a minimum kernel radius for ignition of 1 mm was observed. The short-mode of ignition failure was suppressed by increasing the laser energy and, consequently, the initial kernel size. Nevertheless, the ignitability of lean mixtures was only effectively improved through high-energy sparks and partial prevaporisation of the fuel. Virtually all kernels ignited once prevaporisation was increased, and the gas-phase equivalence ratio was approximately 75% of the lower flammability limit, with ignition being limited only by laser breakdown. [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Combustion & Flame is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1016/j.combustflame.2018.10.009 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 14 StartPage: 387 Subjects: – SubjectFull: Turbulent flow Type: general – SubjectFull: Laser beams Type: general – SubjectFull: Mixtures Type: general – SubjectFull: Turbulence Type: general – SubjectFull: Wavenumber Type: general Titles: – TitleFull: Ignition of uniform droplet-laden weakly turbulent flows following a laser spark. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: de Oliveira, Pedro M. – PersonEntity: Name: NameFull: Allison, Patton M. – PersonEntity: Name: NameFull: Mastorakos, Epaminondas IsPartOfRelationships: – BibEntity: Dates: – D: 01 M: 01 Text: Jan2019 Type: published Y: 2019 Identifiers: – Type: issn-print Value: 00102180 Numbering: – Type: volume Value: 199 Titles: – TitleFull: Combustion & Flame Type: main |
| ResultId | 1 |
