Simultaneous measurements of temperature and CO mole fraction in combustion environment using TDL near 2.3 μm

摘要

Simultaneous measurements of temperature and carbon monoxide (CO) mole fraction in combustion gases using Tunable Diode Laser (TDL) sensor are reported. The sensor is based on absorption transitions (v'=2, v"=0) and (v'=3, v"=1) in the first overtone band of CO near 2.3 μm (～ 4250 cm~(-1)). This band is relatively free of interference from CO_2 and H_2O, and the transitions in the first band are significantly stronger (10~2 times) compared to the second band near 1.5 μm (～ 6300 cm~(-1)). The measurements reported here were completed in the post flame environment of fuel rich premixed ethylene-air flames established on a water cooled McKenna burner. Co-flow of nitrogen was used to stabilize the flame. CO transitions (R 27 and R 6) were probed simultaneously using current tuning of the laser at constant temperature. Due to large difference in lower state energies, the selected line pair offered good sensitivity over the temperature range (1200 - 2200 K) of combustion products. Measurements at steady conditions were done at 100 Hz to minimize the noise and beam steering effects. The absorption due to cooler CO in the axi-symmetric mixing layer of the shroud flow was considered in the data analysis. Temperature measurements with the boundary layer correction show good agreement with N_2 vibrational CARS measurements. CO mole fraction measurements are in qualitative agreement with the equilibrium values.