Optical diagnostics on a catalytic burner

Abstract

Coherent Anti-Stokes Raman Scattering (CARS) and OH chemiluminescence measurements on a catalytic burner are presented and supplemented by probe measurements of gas concentration. The CARS set up is shown and measurement results are discussed. The tested prototype burner is scheduled to achieve NOx emission reductions if used in power plants and therefore could contribute to the precaution of forest dieback or ozone decomposition. In the scope of the “EU project Cathlean” a real size catalytic burner operated with natural gas was tested under atmospheric conditions. The tests were performed at the optical accessible Atmospheric Sector Combustor (ASC, diameter 500 mm) of the Institute of Propulsion Technology. Nitrogen CARS thermometry was performed at two equivalence ratios. The radial profile of mean temperature and single pulse temperature PDF´s were measured downstream the burner exit. Depending on the probe volume location bimodal temperature PDF´s were found. These were probably caused by the hot pilot lance diffusion flame and the colder premixed and pre-reacted exhaust gas downstream the catalyst. This interpretation was also supported by the OH chemiluminescence measurements, which showed a spatial and temporal variation of heat release and gave an overall impression of the flame localisation. These results were used to determine the locations for the CARS point measurements. Due to the flame symmetry the CARS measurements were restricted to one half of the combustor. Also, the results of the gas concentration measurements were consistent with the CARS results and proved the potential of the burner concept for NOx concentration reduction. Nevertheless, single pulse temperatures above 1800 K (the range for increased NOx production) were still found in the CARS temperature PDF´s. The capability of CARS to access the high and low temperature range in the same data ensemble offers a quantitative feedback information for the optimisation of burner design. Additionally, the improvement in understanding of catalytic combustion in real size combustors is supported by the two dimensional, time resolved OH chemiluminescence results and time averaged probe measurements of molecular concentrations.