In situ combustion measurements of CO, CO2, H2O and temperature using diode laser absorption sensors

A diode-laser sensor system based on absorption spectroscopy techniques has been developed to measure CO, CO2, and H2O concentrations and gas temperature non-intrusively in the combustion and exhaust regions above a C2H4-air burner operating at atmospheric pressure. In situ measurements of CO concentration in the combustion region (1.5 cm above the burner) and in the exhaust (79 cm above die burner) were determined from absorption lineshapes of the R(30) and R(15) transitions (2v band) near 2.3 mum, respectively, using new research-grade GaSb-based diode lasers. A minimum detectivity of less than 10 ppm was demonstrated in the exhaust region. In situ measurements of H2O concentration and gas temperature were determined from absorption lineshapes near 1.343 mum (v(1) + v(3) band), 1.392 mum (2v(1), v(1) + v(3) bands), and 1.799 mum (2v(2) + v(3) <-- v(2) band) using distributed feedback (DFB) diode lasers. In situ measurements of CO2 were recorded using a DFB laser near 1.997 mum (R [50] transition, v(1) + 2v(2) + v(3) band). Gas temperature and H2O and CO2 concentrations were monitored simultaneously along a single path in the combustion region (1.5 cm above the burner surface) using a wavelength-multiplexing arrangement. The CO, CO2, and H2O concentration measurements in the combustion region agreed with calculated equilibrium populations to within the experimental uncertainty (10% for CO2 and H2O, 5% for CO), and the measured temperatures were in agreement with radiation-corrected type-S thermocouple values to within 4%. These results demonstrate the utility of diode laser sensors for fast in situ measurements of multiple important combustion parameters for emissions-monitoring and closed-loop control applications.