Diode-laser sensors for real-time control of pulsed combustion systems

A diode-laser based, closed-loop control system has been developed to nonintrusively optimize a pulsed, 50-kW dump combustor. The adaptive control system used temperature and water mole fraction measurements obtained at 10-kHz rates from the peak absorbance values of H2O features near 1.4 mu m. In addition, measurements of CO, C2H2, and C2H4 concentrations in the exhaust, determined from diode-laser absorption spectra recorded using a fast-sampling probe and a multipass absorption cell (nominal 33-m-long path), were used to evaluate the effectiveness of the control strategies. A correlation was established between the magnitude of the observed temperature oscillations and the measured CO concentration in the exhaust. Adaptive control strategies were then applied to maximize the coherence of the burning vortices in the combustion region and thus optimize the combustor performance. The closed-loop control system was able to adaptively tune the phase and amplitude of the applied forcing within 100 ms and the forcing frequency within 10 s. These results demonstrate the applicability of multiplexed diode-laser absorption sensors for rapid, continuous measurements and control of multiple flowfield parameters, including trace species concentrations, in high-temperature combustion environments.