Commenced in January 2007
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Investigating the Effect of Fuel Composition and Concentration on Intrinsic Flame Instabilities in Lean H₂-CO-Air Mixtures Using OH-PLIF

Authors: Kajetan Planötscher, Daniel Heilbronn, Thomas Sattelmayer, Agnes Jocher

Abstract:

In large scale accident scenarios of nuclear power plants core meltdown and molten-core-concrete-interaction can occur. Large amounts of syngas consisting of hydrogen (H₂) and carbon monoxide (CO) might be formed and mixed with the surrounding air. As a result, a flammable and potentially explosive gas mixture is created. Ignition of the flammable mixture might lead to the destruction of the reactor building, causing the detachment of radioactive substances to the environment. In order to prevent future accidents, the understanding of combustion in syngas-air mixtures, in specific the flame topology, has to be improved. Former studies in the context of nuclear safety have investigated the flame topology of H2 flames in lean conditions. Conventional measurement techniques, as well as optical measurement systems, were used to characterize the H₂ flame topology at ignition and early stages of flame propagation. However, to the author’s knowledge, insufficient data on flame topology investigating ignition and early stages of flame propagation in lean H₂-CO-air mixtures is available. In this study, recent improvements to the explosion channel (GraVent test rig) at Technical University of Munich enable the ignition of H₂-CO-air mixtures at fuel concentrations below the fuel concentrations already investigated and therefore allow to extend the available data on flame topology of lean, premixed H₂-CO-air flames. The experiments are carried out using the GraVent explosion channel in its configuration of 1.3 m in length and rectangular cross section of 300 x 60 mm. Additionally, the GraVent test rig exhibits a quartz glass window enabling the use of optical measurement techniques. In order to analyze the ignition and slow deflagration of H₂-CO-air mixtures, fuel compositions of 100/0, 75/25 and 50/50 vol.-% H₂/CO mixtures are investigated at fuel concentrations between 9 – 15 vol.-% in air. In the course of this study, OH-PLIF is used to determine flame front lengths as well as curvature radii. OH-PLIF was selected because OH radicals only occur in the reaction zone. Thus, OH radicals reproduce the shape of the flame front well and can be used for flame topology investigations. In addition, flame front wrinkling factors as a result of the division of the wrinkled flame front length and the smoothed flame front length are calculated. The results for different fuel compositions and fuel concentrations are compared. The optical experimental data contains the ignition of the gas mixtures as well as early stages of flame propagation. In conclusion, the results gathered in this study provide information on the topology of H₂-CO-air flames under lean conditions that will enhance the understanding of syngas combustion and extend experimental data provided in former studies with relevance to large scale accident scenarios of nuclear power plants.

Keywords: flame front wrinkling factor, hydrogen-carbon monoxide-air flames, nuclear safety, OH-PLIF

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