Farooq A, Jeffries J B, Hanson R K
High Temperature Gasdynamics Laboratory, Department of Mechanical Engineering,Stanford University, Stanford, California 94305, USA.
Appl Opt. 2009 Dec 10;48(35):6740-53. doi: 10.1364/AO.48.006740.
Tunable diode lasers (TDL) near 2.7 mum are used to measure high-resolution direct absorption and wavelength modulation with second harmonic (WMS-2f) spectra at high pressures for two CO(2) transitions near 3633.08 and 3645.20 cm(-1), belonging to the nu(1)+ nu(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) CO(2)-Ar mixture. The WMS spectra are shown to be negligibly affected by non-Lorentzian effects up to 10 atm and room temperature, in contrast with direct absorption. Measurements of CO(2) concentration and temperature are carried out in nonreactive shock-tube experiments (P approximately 8-12 atm, T~800-1200 K) to validate the accuracy and precision of wavelength-modulation-spectroscopy-based sensing. CO(2) 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.
波长接近2.7μm的可调谐二极管激光器（TDL）用于在高压下对属于ν(1)+ν(3)振动带、波数分别接近3633.08和3645.20 cm⁻¹的两条CO₂跃迁谱线进行高分辨率直接吸收测量和二次谐波波长调制光谱（WMS-2f）测量。讨论了影响高压TDL传感器设计的重要因素以及WMS-2f线型随压力和激光参数变化的情况。在常压高温池中对3645.20 cm⁻¹跃迁的谱线强度和线宽参数进行了测量。然后使用室温高压池测量两条CO₂跃迁谱线的压力位移。在高密度（9.2阿马格）的CO₂ - Ar混合物中研究了直接吸收光谱和波长调制光谱（WMS）与洛伦兹线型的偏差。结果表明，与直接吸收相比，在高达10个大气压和室温下，WMS光谱受非洛伦兹效应的影响可忽略不计。在非反应性激波管实验（压力约为8 - 12个大气压，温度约为800 - 1200 K）中进行了CO₂浓度和温度测量，以验证基于波长调制光谱传感的准确性和精度。随后在庚烷点火实验中测量了CO₂的时间历程，并与反应动力学机制进行了比较，以证明该传感器在高压燃烧系统中的应用。
