| 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 (nu1+nu3 band) and 1392 nm (2nu 1, nu1+nu3 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 (XH2O) 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 XH2O 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 Trms 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 ∼ 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 XH2O (in ∼ 10 sec.). Effective feedback control of Trms substantially reduced the measured CO, C2H2, and C2H 4 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. |
