A unique spectroscopic strategy has been developed for laser absorption sensing of carbon monoxide (CO) and carbon dioxide (CO₂) at extreme pressures (P > 50 atm) relevant to modern combustion devices. The strategy exploits the band narrowing effects of line mixing, which acutely impact spectrally dense regions, such as bandheads, where line spacing is small. Line mixing is shown to counter collisional line-broadening effects that reduce differential absorption at elevated pressures and often limit the pressure range of laser absorption methods. In this work, the R-branch bandheads of CO and CO₂, which are only observed at high temperatures relevant to combustion, are targeted near 2.3 µm and 4.2 µm, respectively. Spectral line-mixing models were developed for each bandhead region to account for the collision-induced population transfer rates between rotational energy states over a wide range of elevated temperatures and pressures. Modified-exponential-gap models using the relaxation matrix formalism were shown to capture the thermodynamic dependence of the population transfer rates and enabled scaling. Differential absorption at the bandheads was observed to increase by up to a factor of ten at high gas densities, due to line-mixing effects, enabling detection with relatively narrow-band tunable semi-conductor lasers. With refined spectroscopic models, laser absorption measurements of temperature, CO, and CO₂ were demonstrated over a range of high pressures (up to 104 atm) in a sub-scale rocket combustor operated with kerosene and supercritical methane.

已经开发出一种独特的光谱策略，用于在与现代燃烧设备相关的极端压力（P> 50 atm）下对一氧化碳（CO）和二氧化碳（CO ₂）进行激光吸收感测。该策略利用了行混频的频带变窄效应，这会严重影响行间距较小的频谱密集区域（例如带头）。管线混合显示出可以抵消碰撞管线的展宽效应，该效应减少了在高压下的吸收差异，并经常限制激光吸收方法的压力范围。在这项工作中，CO和CO ₂的R分支带头仅在与燃烧有关的高温下才观察到的分别定为2.3 µm和4.2 µm。针对每个带头区域开发了谱线混合模型，以说明在宽范围的高温和高压下，碰撞诱导的旋转能态之间的种群转移速率。使用弛豫矩阵形式主义的修正指数差距模型显示捕获人口转移率和启用缩放的热力学依赖性。在高气体密度下，由于线混合效应，观察到在带头处的差分吸收最多增加了十倍，从而可以使用相对窄带的可调谐半导体激光器进行检测。利用完善的光谱模型，可以测量温度，CO和CO _2的激光吸收率 在使用煤油和超临界甲烷运行的小规模火箭燃烧室中的高压（最高104 atm）范围内进行了演示。