Intra-pulse laser absorption sensor with cavity enhancement for oxidation experiments in a rapid compression machine

Area of Science:

• Spectroscopy
• Laser Technology
• Chemical Kinetics

Background:

• Rapid compression machines (RCMs) are crucial for studying combustion and chemical kinetics.
• Accurate in-situ measurements of species like carbon monoxide (CO) are vital for validating kinetic models.
• Existing measurement techniques may lack the sensitivity or time resolution required for RCM conditions.

Purpose of the Study:

• To develop and demonstrate a highly sensitive sensor for carbon monoxide (CO) detection in RCMs.
• To optimize a mid-infrared pulsed quantum cascade laser (QCL) and off-axis cavity enhanced absorption spectroscopy (OA-CEAS) system for high-pressure, time-resolved measurements.
• To apply the sensor to study CO formation during the oxidation of n-octane.

Main Methods:

• Utilized a mid-infrared pulsed quantum cascade laser (QCL) coupled with off-axis cavity enhanced absorption spectroscopy (OA-CEAS).
• Optimized laser parameters (duty cycle, pulse repetition rate) for enhanced tuning range, chirp rate, and line width to improve laser-cavity coupling.
• Performed spectrally resolved CO line-shape measurements at high pressures (~10 bar) with a demonstrated time resolution of 10 μs and a gain factor of 133.

Main Results:

• Achieved highly sensitive concentration measurements of carbon monoxide (CO).
• Successfully demonstrated spectrally resolved CO line-shape measurements at high pressures (~10 bar).
• Recorded CO concentration-time profiles during the oxidation of dilute n-octane/air mixtures.

Conclusions:

• The developed QCL-OA-CEAS sensor provides a powerful tool for sensitive CO detection in RCMs.
• The sensor's high time resolution and sensitivity enable detailed studies of chemical kinetics during combustion.
• This technology opens new avenues for RCM experiments and kinetic model validation.