Investigations of the long-term effects of LII on soot and bath gas
Type
ArticleKAUST Department
Clean Combustion Research CenterMechanical Engineering Program
Physical Science and Engineering (PSE) Division
high-pressure combustion (HPC) Research Group
Date
2017-08-24Online Publication Date
2017-08-24Print Publication Date
2017-12-02Permanent link to this record
http://hdl.handle.net/10754/625425
Metadata
Show full item recordAbstract
A combination of high-repetition rate imaging, laser extinction measurements, two-colour soot pyrometry imaging, and high-resolution transmission electron microscopy of thermophoretically sampled soot is used to investigate the long-term and permanent effects of rapid heating of in-flame soot during laser-induced incandescence (LII). Experiments are carried out on a laminar non-premixed co-annular ethylene/air flame with various laser fluences. The high-repetition rate images clearly show that the heated and the neighbouring laser-border zones undergo a permanent transformation after the laser pulse, and advect vertically with the flow while the permanent marking is preserved. The soot volume fraction at the heated zone reduces due to the sublimation of soot and the subsequent enhanced oxidation. At the laser-border zones, however, optical thickness increases that may be due to thermophoretic forces drawing hot particles towards relatively cooler zones and the rapid compression of the bath gas induced by the pressure waves created by the expansion of the desorbed carbon clusters. Additionally sublimed carbon clusters can condense onto existing particles and contribute to increase of the optical thickness. Time-resolved two-colour pyrometry imaging show that the increased temperature of soot both in the heated and neighbouring laser-border zones persists for several milliseconds. This can be associated to the increase in the bath-gas temperature, and a change in the wavelength-dependent emissivity of soot particles induced by the thermal annealing of soot. Ex-situ analysis show that the lattice structure of the soot sampled at the laser-border zones tend to change and soot becomes more graphitic. This may be attributed to thermal annealing induced by elevated temperature.Citation
Cenker E, Bennett A, Roberts WL (2017) Investigations of the long-term effects of LII on soot and bath gas. Aerosol Science and Technology: 00–00. Available: http://dx.doi.org/10.1080/02786826.2017.1368444.Sponsors
The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST).Publisher
Informa UK LimitedJournal
Aerosol Science and TechnologyAdditional Links
http://www.tandfonline.com/doi/full/10.1080/02786826.2017.1368444Relations
Is Supplemented By:- [Dataset]
E. Cenker, A. Bennett, & W. L. Roberts. (2017). Investigations of the long-term effects of LII on soot and bath gas [Data set]. Taylor & Francis. https://doi.org/10.6084/M9.FIGSHARE.5341276.V1. DOI: 10.6084/m9.figshare.5341276.v1 Handle: 10754/663814
ae974a485f413a2113503eed53cd6c53
10.1080/02786826.2017.1368444