<title>Diode laser sensor system for closed-loop control of a 50-kw incinerator</title>

Abstract

A multiplexed diode-laser absorption sensor system, comprised of two distributed feedback (DFB) InGaAsP diode lasers and fiber-optic components, has been developed to non-intrusively measure gas temperature and H 2 O concentration over a single path in the combustion region of a 50-kW model pulsed incinerator. The wavelengths of the DFB lasers were independently current-tuned at 10-kHz rates across H 2 O transitions near 1343 nm (v 1 +v 3 band) and 1392 nm (2v 1 , v 1 +v 3 bands). Temperature was determined (at I00-ps intervals) from the ratio of measured peak absorbances and used for closed-loop control of the combustor. In addition, measurements of CO, CO 2 , and C 2 H 4 concentrations were determined from absorption spectra recorded in the incinerator exhaust using a fast-sampling stainless steel, water-cooled probe and a multi-pass absorption cell (nominal 36-m long path). An external cavity diode laser was tuned over the CO R(13) transition (3v band) near 1568 nm and the CO 2 R(16) transition (2vj+2v 2 +v 3 band) near 1572 nm, and a DFB laser was tuned over selected C 2 li4 transitions (v i +v 9 , v s +v 9 bands) near 1646 nm. A correlation was established between the magnitude of the observed temperature fluctuations and the measured CO concentration in the exhaust. The amplitude of temperature fluctuations was controlled in a feedback loop by adjusting the relative phase between the primary and secondary forced air flows. The results obtained 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.