High-Pressure Measurements of Temperature and CO 2 Concentration Using Tunable Diode Lasers at 2 μm

Abstract

A sensor for simultaneous measurements of temperature and carbon dioxide (CO₂) concentration at elevated pressure is developed using tunable diode lasers at 2 µm. Based on some selection rules, a CO₂ line pair at 5006.140 and 5010.725 cm⁻¹ is selected for the TDL sensor. In order to ensure the accuracy and rapidity of the sensor, a quasi-fixed-wavelength WMS is employed. Normalization of the 2f signal with the 1f signal magnitude is used to remove the need for calibration and correct for transmission variation due to beam steering, mechanical misalignments, soot, and windows fouling. Temperatures are obtained from comparison of the background-subtracted 1f-normalized WMS-2f signals ratio and a 1f-normalized WMS-2f peak values ratio model. CO₂ concentration is inferred from the 1f-normalized WMS-2f peak values of the CO₂ transition at 5006.140 cm⁻¹. Measurements of temperature and CO₂ concentration are carried out in static cell experiments (P = 1–10 atm, T = 500–1200 K) to validate the accuracy and ability of the sensor. The results show that accuracy of the sensor for temperature and CO₂ concentration are 1.66% temperature and 3.1%, respectively. All the measurements show the potential utility of the sensor for combustion diagnose at elevated pressure.