Abstract
This thesis gives an introduction to pulsed cavity ring-down absorption spectroscopy (CRDS) and its application in combustion research. Experimental results have been compared to numerical simulations, providing a means to validate reaction mechanisms and numerical approaches. Up to now, the application of CRDS in the field of combustion research has mainly been focused on sub-atmospheric flames and quantitative investigations of atmospheric flames have been very limited. Here, it has been applied to study OH and CH radicals in the flame of a premixed methane/air flat flame burner at atmospheric pressure to obtain temperatures and concentrations and to study the effect of the laser bandwidth on the experimental results. Statistical, analytical and Abel inversion methods have been used to make a correct comparison of the experimental data with numerical simulations. In addition to these radicals, the singlet methylene radical CH2 and the formyl radical HCO have also been studied. Because the density profiles of both radicals are positioned very close to the burner surface at atmospheric pressures, it is difficult to obtain complete density distributions for both radicals. The numerical simulations show a qualitative and quantitative good agreement with the experimental 1CH2 and HCO density profiles and the numerical simulations. In addition, results on OH and HCO obtained from a low-pressure flat flame are given. Finally, the method has been applied for trace gas detection of NO and NO2, collectively called NOx. Nitrogen dioxide has been detected in the burned gas region of an oxyacetylene flame and NO and NO2 in situ in the exhaust gas of a diesel engine running on commercial fuel. The experiments showed that CRDS provides a direct optical method to determine NOx in exhaust gases, which amply meets the sensitivity requirements stated in the European standard directives on the emission of NOx.
