H_2O Number Density and Temperature Measurements in a Rapid Compression Machine using Mid-IR Absorption Spectroscopy

摘要

Transient evolution profile of important species and temperature in well-characterized experimental facility can provide insights into the combustion kinetics and validation database for the refinement of reaction mechanisms. In this investigation, temporal measurements of H_2O number density and temperature are conducted in a rapid compression machine using Mid-IR absorption spectroscopy. Quantum cascade lasers tunable in the mid-infrared (1300-1378 cm~(-1)) region are employed. While the ratio of absorption by two rotational lines of H_2O can be used to determine the temperature, the line broadening of these two lines can be different from each other and also depend on the buffer gases and temperature conditions. This can alter the line ratios, estimated temperatures, and number densities. In addition, the abundant strong absorption lines of H_2O can interfere with absorption signals by other species in the laser wavelength range and affect their quantification. Therefore, it is important to quantify the number density of H_2O accurately. For this reason, the line by line pressure dependence through the air broadened half widths (γ) and temperature dependence of the broadening through the exponent 'n' in the Hitran database have been extracted through experiments. Air, Ar, and H_2 as buffer gases are investigated in this work. Experiments have been done for temperature conditions of 460 K, 500 K, and 530 K and in the pressure range of 100-650 Torr.