CO_2 concentration and temperature sensor for combustion gases using diode-laser absorption near 2.7 μm

摘要

A new tunable diode-laser sensor based on CO_2 absorption near 2.7 μm is developed for high-resolution absorption measurements of CO_2 concentration and temperature. The sensor probes the R(28) and P(70) transitions of the v_1 + v_3 combination band of CO_2 that has stronger absorption line-strengths than the bands near 1.5 μm and 2.0 μm used previously to sense CO_2 in combustion gases. The increased absorption strength of transitions in this new wavelength range provides greatly enhanced sensitivity and the potential for accurate measurements in combustion gases with short optical path lengths. Simulated high-temperature spectra are surveyed to find candidate CO_2 transitions isolated from water vapor interference. Measurements of line-strength, line position, and collisional broadening parameters are carried out for candidate CO_2 transitions in a heated static cell as a function of temperature and compared to literature values. The accuracy of a fixed-wavelength CO_2 absorption sensor is determined via measurement of known temperature and CO_2 mole fraction in a static cell and shock-tube. Absorption measurements of CO_2 are then made in a laboratory fiat-flame burner and in ignition experiments of shock-heated n-heptane/O_2/argon mixtures to illustrate the potential of this sensor for combustion and reacting-flow applications.