Absorption spectroscopy based high-speed oxygen concentration measurements at elevated gas temperatures

A sensor based on tunable diode laser absorption spectroscopy (TDLAS)has been developed for concentration measurements in high-temperature (up to 800 K)gas streams; while the sensor measures gas oxygen and water concentration, temperature and pressure, this work focuses on the challenges and solutions to transient oxygen measurement. A 760-nm diode laser was used to probe a pair of oxygen absorption transitions, and a Herriott cell based multi-pass arrangement was utilized to compensate for the extremely weak oxygen absorption as well as the high gas temperature. This multi-pass arrangement provides a 4297.4-mm absorption path length across a 76.2-mm diameter duct, and an O₂ detection limit ([O₂]where SNR=1)of ca. 0.1%. Laboratory validation of the HITRAN spectral parameters of the chosen absorption transitions was performed over a range of high temperatures and oxygen concentrations relevant to engine-exhaust applications. The insensitivity of the Herriott cell arrangement to vibrations and spatial temperature gradients was demonstrated. Results from applications to single- and multi-cylinder engine exhaust are presented and demonstrate the new sensor's ability to measure fast intra-cycle gas-property transients, and provide insights relevant to advancing internal-combustion-engine technology.