DIODE-LASER ABSORPTION SPECTROSCOPY APPLIED FOR THE ACTIVE CONTROL OF COMBUSTION (TEMPERATURE, WATER VAPOR).

다국어 초록 (Multilingual Abstract)

Adaptive control strategies which utilize the unique measurement capabilities afforded by diodelaser absorption sensors were developed to measure and control the gas temperature and the water-vapor concentration in various atmospheric-pressure combustors. The wavelengths of two distributed feedback (DFB) InGaAsP diode lasers were current-tuned at 10-kHz rates across H₂O transitions near 1343 nm (ν₁+ν₃ band) and 1392 nm (2ν₁, ν₁+ν₃ bands) to record spectrally-resolved absorption lineshapes. The path-averaged rotational temperature was inferred from the ratio of peak spectral absorption coefficients. The water mole fraction (X_H2O) was then determined from the inferred temperature and the measured absorbance. A closed-loop feedback system was developed to monitor and control the gas temperature of the burned gases in a flat-flame burner. The control system was capable of maintaining the gas temperature to within 1% of the desired value for various set points, with an actuator-limited settling time below 30 ms. The combustion control system was then applied to adaptively control the magnitude and frequency of naturally occurring temperature fluctuations in a ducted burner by oscillating the fuel flow acoustically, reducing these oscillations by 73%. Adaptive strategies were developed to monitor and control X_H2O and the magnitude of forced temperature oscillations (T_rms values) in the combustion region of 5-kW and 50-kW acoustically-forced dump combustors. The feedback system optimized the measured T_rms values in the combustion region by adjusting the phase and amplitude of the fuel forcing, resulting in a rapid increase in the extent of reaction from an uncontrolled level of 47% to 85% in <math> <f> ∼</f> </math>100 ms. The extent of reaction was further increased to 97% by adjusting the actuator power using a secondary control effort which maximized the measured X_H2O (in <math> <f> ∼</f> </math>10 sec.). Effective feedback control of T_rms substantially reduced the measured CO, C₂H₂, and C₂H₄ concentrations in the exhaust. The successful demonstration of closed-loop control in realistic combustion systems illustrates the potential of diode-laser absorption sensors for improved measurement and control of combustion and other high temperature process streams, particularly for applications that require applications that require remote and non-intrusive monitoring.