A sensor based on cavity-enhanced absorption spectroscopy (CEAS) was implemented for the first time in a rapid compression machine (RCM) for carbon monoxide concentration measurements. The sensor consisted of a pulsed quantum cascade laser (QCL) coupled to a low-finesse cavity in the RCM using an off-axis alignment. The QCL was tuned near 4.89 µm to probe the P(23) ro-vibrational line of CO. The pulsed mode operation resulted in rapid frequency down-chirp (6.52 cm⁻¹/µs) within the pulse as well as a high time resolution (10 µs). The combination of rapid frequency down-chirp and off-axis cavity alignment enabled a near complete suppression of the cavity coupling noise. A CEAS gain factor of 133 was demonstrated in experiments, resulting in a much lower noise-equivalent detection limit than a single-pass arrangement. The sensor thus presents many opportunities for measuring CO formation at low temperatures and for studying kinetics using dilute reactive environments; one such application is demonstrated in this work using dilute n-heptane/air mixtures in the RCM. The formation of CO during first-stage ignition of n-heptane was measured over 802–899 K at a nominal pressure of 10 bar. These conditions correspond to the NTC region of n-heptane and such results provide useful metrics to test and compare the predictions of low-temperature heat release by different kinetic models.

基于腔增强吸收光谱（CEAS）的传感器首次在快速压缩机（RCM）中用于一氧化碳浓度测量。该传感器由脉冲量子级联激光器（QCL）组成，该脉冲量子级联激光器通过离轴对准耦合到RCM中的低精细腔。将QCL调谐到4.89 µm附近，以探测CO的P（23）旋转振动线。脉冲模式操作导致快速的频率向下线性调频（6.52 cm ^-1/ µs）和高时间分辨率（10 µs）。快速下调线性调频和离轴腔对准的组合可以几乎完全抑制腔耦合噪声。实验证明，CEAS增益因子为133，从而导致等效噪声的检测极限比单通道测试低得多。因此，该传感器为在低温下测量一氧化碳的形成以及在稀的反应环境中研究动力学提供了许多机会。在这项工作中，使用RCM中的稀正庚烷/空气混合物证明了一种这样的应用。在公称压力为10 bar的情况下，在802-899 K范围内测量了正庚烷第一阶段点火过程中CO的形成。