In situ combustion measurements of H_(2)O and temperature near 2.5 (mu)m using tunable diode laser absorption

摘要

In situ combustion measurements of water vapor concentration and gas temperature were carried out with a new tunable diode laser sensor near 2.5 (mu)m. Recent availability of room-temperature semiconductor diode lasers operating at longer wavelengths provides access to fundamental vibrational bands (v_(1) and v_(3)) of H_(2)O. These bands have stronger absorption line strength compared to the overtone (2v_(1), 2v_(3)) and combination (v_(1) + v_(3)) vibrational bands in the near-infrared region probed previously with telecommunication diode lasers. The absorption transitions of H_(2)O vapor in the 2.5-3.0 (mu)m region are systematically analyzed via spectral simulation, and optimal spectral line pairs are selected for combustion measurements in the temperature range of 1000-2500 K. Fundamental spectroscopic parameters (line strength, line position and line-broadening coefficients) of the selected transitions are determined via laboratory measurements in a heated cell. Absorption measurements of H_(2)O concentration and temperature are then made in a laboratory flat-flame burner to illustrate the potential of this sensor for sensitive and accurate measurements in combustion gases with short optical path lengths.