Direct measurement of S-branch N2-H2 Raman linewidths using time-resolved pure rotational coherent anti-Stokes Raman...

Area of Science:

• Spectroscopy
• Physical Chemistry
• Combustion Science

Background:

• Accurate temperature measurements are critical in combustion processes, particularly in hydrogen diffusion flames.
• Nitrogen (N2) Coherent Anti-Stokes Raman Spectroscopy (CARS) is a valuable non-intrusive thermometry technique.
• Understanding the behavior of N2 in mixtures with hydrogen is essential for reliable thermometry.

Purpose of the Study:

• To measure S-branch N(2)-H(2) Raman linewidths across a wide temperature range (294-1466 K).
• To assess the applicability of N2 CARS thermometry in the fuel-side of H2 diffusion flames.
• To provide a dataset for spectral fitting and validation of thermometry methods.

Main Methods:

• Utilized time-resolved dual-broadband picosecond pure rotational coherent anti-Stokes Raman spectroscopy (RCARS).
• Extracted data by mapping dephasing rates from CARS signal temporal decay.
• Detected J-dependent coherence decays in the time domain by monitoring individual spectral lines with probe delay.

Main Results:

• Measured S-branch N(2)-H(2) Raman linewidths from 294 K to 1466 K.
• Employed linewidth data for spectral fits of N2 RCARS spectra in N2/H2 mixtures up to 661 K.
• Observed less than 2% deviation compared to thermocouples in the calibrated temperature region.

Conclusions:

• The measured linewidths offer valuable insights into N2 CARS thermometry performance.
• The technique shows promise for accurate temperature measurements in H2 diffusion flames.
• The data supports the use of N2 CARS for diagnostics in hydrogen combustion environments.