Measurements of CO₂ concentration and temperature at high pressures using 1 f-normalized wavelength modulation spectroscopy with second harmonic detection near 2.7 μm

Tunable diode lasers (TDL) near 2.7 μm are used to measure high-resolution direct absorption and wavelength modulation with second harmonic (WMS-2f) spectra at high pressures for two CO₂ transitions near 3633.08 and 3645.20cm^-1, belonging to the v₁ + v ₃ vibrational band. Important factors influencing the design of a high-pressure TDL sensor and the variation of WMS-2f line shape with changes in pressure and laser parameters are discussed. Measurements of line strength and line broadening parameters are carried out for the 3645.20 cm^-1 transition in an atmospheric-pressure, high-temperature cell. A room-temperature high-pressure cell is then used to measure the pressure shift for both CO ₂ transitions. Deviation of the direct absorption and wavelength modulation spectroscopy (WMS) spectra from the Lorentzian profile is studied in a high-density (9.2 amagats) CO₂-Ar mixture. The WMS spectra are shown to be negligibly affected by non-Lorentzian effects up to 10atm and room temperature, in contrast with direct absorption. Measurements of CO₂ concentration and temperature are carried out in nonreac-tive shock-tube experiments (P ∼ 8-12 atm, T ∼ 800-1200 K) to validate the accuracy and precision of wavelength-modulation-spectroscopy-based sensing. CO₂ time histories are then measured in heptane ignition experiments and compared with reaction kinetics mechanisms to demonstrate the use of this sensor in high-pressure combustion systems. copy; 2009 Optical Society of America.