Quantum cascade laser based MIR spectrometer for the determination of CO and CO2 concentrations and temperature in flames

An experimental setup for the simultaneous detection of CO and \(\hbox {CO}_2\) and the temperature in low-pressure flames using a pulsed quantum cascade laser at 4.48 μm is presented. This comparatively new type of laser offers good output energies and beam quality in the mid-infrared, where the strong fundamental transitions of many molecules of interest can be accessed. A single-pass absorption setup was sufficient to obtain good accuracy for the stable species investigated here. Due to the high repetition rate of the laser and the speed of the data acquisition, measurement of two-dimensional absorption spectra and subsequent tomographic reconstruction was feasible. As demonstration of this technique, two-dimensional CO and \(\hbox {CO}_2\) concentrations have been measured in two fuel-rich methane flames with different coflow gases (nitrogen and air). The influence of the coflow gas on the flame center concentration profiles was investigated and compared with one-dimensional model simulations.