Pressure dependence occurs in bimolecular hydrogen abstraction reactions at combustion, atmospheric and interstellar temperatures.

A mid-infrared two-line thermometry based on H₂O absorption was developed for in situ and sensitive temperature measurements of laminar flames. The H₂O absorption lines in v₃ fundamental band were systematically investigated and a new promising line pair (4029.52 cm^–1 and 4030.73 cm^–1) was selected to achieve strong absorption line-strength and high-temperature sensitivity over the temperature range of 1000–3000 K. This line pair was readily assessed by a single current scan of a distributed feedback laser near 2.5 μm. The scanned-wavelength laser absorption strategy was adopted for temperature measurements for both laminar sooting and non-sooting flames. This optical sensor was applied in measuring various flame conditions including CH₄/air and C₂H₄/air premixed flames (Ф = 0.8–1.2), C₂H₄/air sooting flames (Ф = 1.78–2.38), and partially premixed flames. Our measurements were in good agreement with thermocouple measurements for all the flame conditions. In addition, numerical simulations using the detailed chemical kinetic mechanisms (CH₄ flame: GRI 3.0, C₂H₄ flame: USC 2.0) were conducted to validate the experimental results.

We report the influence of absorption line selection on the tomographic results for high-temperature flames by numerical and experimental methods. Different combinations of infrared H ₂ O absorption transitions are utilized with the Tikhonov-regularized Abel inversion to reconstruct the radial distribution of temperature and H ₂ O concentration in a flat flame. It is shown that besides using the mathematical algorithm such as regularization, selecting a line pair with a large Δ E″ (>1390 cm ⁻¹ ) also reduces the reconstruction uncertainty at 300–2000 K. In this study, a proper selection of absorption line pairs reduces the reconstruction uncertainty by 25% at the same level of noise. The line pair of H ₂ O transitions at 4029.524 cm ⁻¹ and 4030.729 cm ⁻¹ is recommended for the tomography of high-temperature flames at 1000–3000 K, whereas the line pair of 7185.597 cm ⁻¹ and 7444.352 cm ⁻¹ can be used at 300–1000 K.

We report the development and application of a compact and sensitive mid-infrared nitric oxide (NO) sensor using off-beam quartz-enhanced photoacoustic spectroscopy (QEPAS). This QEPAS sensor exploits the strong absorption band of NO at 5.2 μm using a distributed-feedback quantum cascade laser (QCL). The QCL was connected with the custom-designed photoacoustic gas cell with a mid-infrared multimode fiber to form a plug-and-play system. The selection of key sensor parameters, such as micro-resonator, laser modulation depth, and gas pressure, was discussed in detail about improving the detection sensitivity. With a minimum detection limit of 120 ppbv, our QEPAS NO sensor was deployed in real-time diesel-engine exhaust monitoring. We observed the influence of soot existing in the engine exhaust on the sensor performance, which was filtered by a high efficiency particulate arrestance material. Our sensor captured the varied NO concentrations between 126 and 187 ppmv in the exhaust at different engine rotational speeds.