Tomographic analysis of CO absorption in a low-pressure flame

Area of Science:

• Combustion science
• Laser diagnostics
• Thermometry

Background:

• Accurate temperature measurements are crucial for understanding combustion processes.
• Low-pressure flames present unique challenges for diagnostic techniques.
• Tunable diode laser absorption spectroscopy (TDLAS) with CO two-line thermometry is a common method for flame temperature determination.

Purpose of the Study:

• To apply tomographic analysis for correcting low-pressure stoichiometric premixed methane/oxygen flame temperatures.
• To investigate the accuracy of line-of-sight TDLAS measurements in low-pressure flames.
• To understand the spatial distribution of temperature and vibrational populations in these flames.

Main Methods:

• Utilized tomographic analysis to reconstruct 3D temperature fields.
• Employed tunable diode laser absorption spectroscopy (TDLAS) with CO two-line thermometry.
• Conducted experiments on low-pressure stoichiometric premixed CH(4)/O(2) flames.

Main Results:

• Line-of-sight measurements consistently underestimated flame temperatures.
• The temperature correction is a nonlinear function of height above the burner.
• Constant temperature across the flame at a given height does not imply constant vibrational populations.
• Low-pressure flames (<20 Torr) exhibit radial spread beyond the burner, invalidating 1D models.

Conclusions:

• Tomographic analysis provides essential corrections for TDLAS measurements in low-pressure flames.
• Spatial variations in temperature and vibrational populations are significant and must be accounted for.
• One-dimensional models are inadequate for low-pressure flames due to radial spread.