Recent advances in laser absorption and shock tube methods for studies of combustion chemistry

Abstract

Recent advances in laser absorption and shock tube methodologies for studies of combustion chemistry are reviewed. First the principles of shock tube operation are discussed, and then an overview of shock tube diagnostic methods and experiments is covered. Recent shock tube developments include the use of driver inserts to counteract the small pressure gradient seen in conventional reflected shock wave experiments and the use of a constrained-reaction-volume strategy to enable the implementation of near-constant-pressure gasdynamic test conditions during energetic processes. Recent laser absorption developments include the use of a CO2 laser absorption sensor to accurately monitor temperature during shock wave experiments, the use of multi-wavelength laser absorption strategies to simultaneously monitor multiple species time-histories, and the used of isotopic labeling strategies to identify individual reaction sites during the measurement of elementary reaction rate constants. The improved ability to accurately constrain the test conditions in shock tube experiments, combined with non-intrusive, species-sensitive and quantitative laser absorption diagnostics, is enabling experimenters to provide a new generation of high-quality experimental kinetics targets for combustion chemistry model validation and refinement. The paper concludes with a brief discussion of newly emerging laser-diagnostic techniques and a summary of future research directions.