Experimental and Numerical comparison of extractive and in situ laser measurements of non-equilibrium carbon monoxide in lean-premixed natural gas combustion

Abstract

Measurements of carbon monoxide (CO) in the high-temperature combustion product stream of an atmospheric pressure, lean-premixed combustion, natural gas reactor were obtained using line-of-sight tunable diode laser absorption and extractive probe sampling in conjuction with nondispersive infrared analyzers over various equivalence ratios and flow residence times. The measurements are compared with (1) a numerical model using comprehensive chemical kinetics for methane combustion in conjunction with perfectly stirred reactor (PSR) and plug-flow reactor (PFR) modeling approaches, and (2) chemical equilibrium at the measured temperatures. Temperatures ranging from 1500 to 2000 K were measured using a radiation corrected thermocouple and also by a diode laser thermometry technique. The laser based in situ measurements of CO concentration ranged from 50 to 5000 ppm depending on the equivalence ratio and flow residence time. Results of the numerical model were consistent with the laser-based measurements. The extractive probe measurements were found to be as much as 10 times less than the laser-based measurements. However, laser and probe measurements for fuel-rich equivalence ratios agreed. In an effort to improve the performance of extractive sampling probes, we tested several aerodynamic quench probe designs. We were unable to achieve an aerodynamic quench of the CO in a high-temperature combustion product stream. A model of the sampling probe as a PFR indicates that extractive sampling of [CO] is increasingly inaccurate at gas temperatures above 1000 K.