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Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes
Published on: May 26, 2014
Two-point time-series measurementsof hydroxyl concentration in a turbulent nonpremixed flame
Jiayao Zhang1, Galen B King, Normand M Laurendeau
1School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, USA. zhang46@ecn.purdue.edu
Applied Optics
|August 19, 2007
Summary
This study introduces a novel two-point hydroxyl (OH) measurement technique for turbulent flames. Improved diagnostics reveal how OH length scales evolve in flames, offering insights into turbulent combustion.
Area of Science:
- Combustion Science
- Laser Diagnostics
- Turbulent Flow Physics
Background:
- Accurate characterization of turbulent nonpremixed flames is crucial for understanding combustion processes.
- Previous two-point measurements were limited by optical aberrations and signal noise.
- Hydroxyl radical (OH) is a key species for flame diagnostics.
Purpose of the Study:
- To apply and validate an improved two-point picosecond time-resolved laser-induced fluorescence (LIF) system for quantitative OH measurements in turbulent flames.
- To investigate the spatial and temporal characteristics of OH distributions and length scales.
- To assess the impact of optical aberrations and fluorescence lifetime fluctuations on measurement accuracy.
Main Methods:
- Utilized a picosecond time-resolved two-point laser-induced fluorescence (LIF) diagnostic system.
- Implemented a newly designed collection system to minimize optical aberrations (blur spot reduced to 180 microm).
- Employed photon-counting channels and a triple-bin integration method for absolute OH concentration recovery.
- Applied noise reduction schemes for two-point statistics and analyzed spatial autocorrelation functions.
Main Results:
- Successfully applied the two-point OH LIF technique to turbulent nonpremixed flames for the first time.
- Demonstrated that optical aberrations significantly affect space-time correlations, but not integral length scales.
- Observed that hydroxyl integral length scales increase linearly with axial distance at peak OH concentrations.
- Found that OH length scales on the jet centerline increase rapidly above the flame tip.
Conclusions:
- The improved two-point LIF technique provides accurate quantitative OH measurements in turbulent flames.
- Hydroxyl integral length scales exhibit distinct axial trends, rising with distance and above the flame tip.
- OH length and time scales show similar trends along the centerline but opposite trends at peak OH locations.
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