Spatial and temporal evolution of laser-induced flame kernels in a methane jet injected into air
File(s)
Published version
Author(s)
Chen, Chaoxu
Hardalupas, Yannis
Taylor, Alex MKP
Type
Journal Article
Abstract
We report the first measurements of the evolution of laser-induced flame kernels in a methane jet (nozzle
diameter D = 2 mm, injection velocity U = 20.0 m/s) as a function of laser energy (E = 50–80 mJ) and beam
orientation, along either the jet’s axial or radial direction. Kernels were initiated at x = 10 D axially and r = − 1 D
radially, for high probability of successful ignition, where the mean mole fraction of methane was 0.19. Flame
kernel evolution within t = 1–10 ms after ignition laser pulse was quantified for kernel projected area, lumi
nosity, shape, location, and propagation of kernel edges. Within t = 1–3 ms, the kernel extended beyond the jet’s
nominal flammable regions for both orientations, attributed to mixture transport by the spark-induced gas
motions. For the radially-orientated beam, these motions led to a three-lobe structure of the kernel: this structure
was absent for the axially-orientated beam. Development after t = 5 ms was primarily along the jet’s nominal
flammable regions for both orientations. The kernel’s projected area and integrated luminosity grew according to
a power law, regardless of the pulse energy and beam orientation; both variables increased approximately lin
early with E, but reduced by half when orientation changed from radial to axial. Fluctuations of the kernel’s
location reduced with increased E, and were insensitive to the beam orientation. For the radially-orientated beam
with E = 80 mJ, the kernel’s r-minus edge first moved away from, then towards, and eventually away from the
jet axis, probably driven by spark-induced gas motions; as E reduced this gradually changed to consistent motion
away from the axis. For the axially-orientated beam, this edge moved only after t = 5 ms, away from the axis. The
speeds of the kernel’s x-minus and x-plus edges, moving relative to the flow, were estimated from the speeds
measured in laboratory coordinates. That of the x-minus edge was about five to six times methane’s stoichio
metric laminar burning velocity (SL) for both beam orientations; that of the x-plus edge was slightly higher than
SL, but only half SL, respectively for the radially- and axially-orientated beams.
diameter D = 2 mm, injection velocity U = 20.0 m/s) as a function of laser energy (E = 50–80 mJ) and beam
orientation, along either the jet’s axial or radial direction. Kernels were initiated at x = 10 D axially and r = − 1 D
radially, for high probability of successful ignition, where the mean mole fraction of methane was 0.19. Flame
kernel evolution within t = 1–10 ms after ignition laser pulse was quantified for kernel projected area, lumi
nosity, shape, location, and propagation of kernel edges. Within t = 1–3 ms, the kernel extended beyond the jet’s
nominal flammable regions for both orientations, attributed to mixture transport by the spark-induced gas
motions. For the radially-orientated beam, these motions led to a three-lobe structure of the kernel: this structure
was absent for the axially-orientated beam. Development after t = 5 ms was primarily along the jet’s nominal
flammable regions for both orientations. The kernel’s projected area and integrated luminosity grew according to
a power law, regardless of the pulse energy and beam orientation; both variables increased approximately lin
early with E, but reduced by half when orientation changed from radial to axial. Fluctuations of the kernel’s
location reduced with increased E, and were insensitive to the beam orientation. For the radially-orientated beam
with E = 80 mJ, the kernel’s r-minus edge first moved away from, then towards, and eventually away from the
jet axis, probably driven by spark-induced gas motions; as E reduced this gradually changed to consistent motion
away from the axis. For the axially-orientated beam, this edge moved only after t = 5 ms, away from the axis. The
speeds of the kernel’s x-minus and x-plus edges, moving relative to the flow, were estimated from the speeds
measured in laboratory coordinates. That of the x-minus edge was about five to six times methane’s stoichio
metric laminar burning velocity (SL) for both beam orientations; that of the x-plus edge was slightly higher than
SL, but only half SL, respectively for the radially- and axially-orientated beams.
Date Issued
2025-04-15
Date Acceptance
2025-01-03
Citation
Fuel, 2025, 386
ISSN
0016-2361
Publisher
Elsevier BV
Journal / Book Title
Fuel
Volume
386
Copyright Statement
© 2025 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
License URL
Identifier
https://doi.org/10.1016/j.fuel.2025.134304
Publication Status
Published
Article Number
134304
Date Publish Online
2025-01-08