Abstract
A wavelength-multiplexed, diode-laser absorption sensor system, comprised of two distributed feedback (DFB) In GaAsP diode lasers and fiber-optic components, has been developed to nonintrusively measure gas temperature and H2O concentration over a single path in the combustion region of a 5-kW, atmospheric-pressure, non-premixed, annular dump combustor. The wavelengths of the DFB lasers were independently current-tuned at 10-kHz rates across H2O transitions near 1343 nm (v1+v3 band) and 1392 nm (2v1, v1+v3 bands). Temperature was determined from the ratio of measured peak absorbances. Water-vapor mole fraction was determined from the measured absorbance and gas temperature values. The diode-laser sensors were applied for closed-loop control of the combustor, which utilized the concepts of acoustic forcing to improve the fuel-air mixing and thus the combustion efficiency. Adaptive control strategies were investigated that used the measured mean H2O concentration and the instantaneous temperature as sensed parameters. The relative phase between the acoustic forcing of the central air and the fuel (C2H4) flow, as well as the fuel-forcing amplitude, was adjusted to maximize the coherence and the extent of reaction in the combustion region and thus optimize the combustor performance. The closedloop control system was able to adaptively optimize the combustor performance within 100 ms, which corresponded to seven characteristic time constants of the actuator. The results obtained demonstrate the applicability of multiplexed diode-laser absorption sensors for rapid, continuous measurements and control of multiple flowfield parameters in high-temperature combustion environments.
Published Version
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