Vibrationally excited hydroxyl tagging velocimetry

Area of Science:

• Combustion science
• Laser-based diagnostics
• Molecular physics

Background:

• Accurate velocity measurements are crucial for understanding combustion dynamics.
• Existing methods face challenges in high-temperature, high-speed environments with background species.
• Hydroxyl tagging velocimetry (HTV) offers a promising approach for in-situ measurements.

Purpose of the Study:

• To develop and validate a novel molecular-based velocity measurement technique for high-temperature flame gases.
• To adapt the hydroxyl tagging velocimetry (HTV) technique for enhanced sensitivity and temporal resolution.
• To demonstrate the capability of the new method in turbulent premixed flames.

Main Methods:

• Development of vibrationally excited HTV (VE-HTV) using a KrF laser (248 nm) to create a OH (v=1) tag from H2O dissociation.
• Selective detection of the excited OH tag (v=1) against the background of ground-state OH (v=0).
• Single-shot velocity measurements along a 2 cm line in atmospheric pressure laboratory burners at temperatures up to 2300 K.

Main Results:

• The OH (v=1) tag demonstrated a persistence of 5-10 μs, suitable for single-shot measurements.
• Successful velocity measurements were achieved across lean, stoichiometric, and rich flame conditions.
• Mean velocity measurements were validated in a lean H2/air turbulent flame (ϕ=0.78, Re=26,550).

Conclusions:

• The developed VE-HTV method provides a robust tool for high-speed velocity measurements in hot combustion environments.
• The technique is particularly effective in the presence of significant background OH concentrations.
• VE-HTV advances the field of laser-based combustion diagnostics, enabling more detailed flame analysis.