New Directions in Ultrashort Pulse Laser Diagnostics: Towards Collision-Independent Multi-Species Detection and Imaging in Harsh Chemical Environments
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abstract
State-of-the-art, nonintrusive optical and laser-based diagnostic methods can unveil tremendous opportunities for scientists and engineers designing next generation engines, power plants, propulsion systems, chemical and plasma processing facilities, among many others. The overarching goal of this research project is to develop novel species measurement technique to characterize fundamental physical and chemical processes in harsh environments such as those present in modern gas turbine combustor and IC engines. The new techniques developed here have the potential to uncover quantitative, spatially and temporally resolved key intermediate species measurements in reacting flow systems by using the latest developments in the ultrashort pulse laser technology. In addition to primary research outcomes, graduate and undergraduate students including minorities and underrepresented groups are trained in unique, next-generation laser fundamentals and applications. Students work in multidisciplinary research environments and often interact with outside research teams, preparing them for successful future careers in optics and energy related technologies. Research findings will be incorporated into ongoing curriculum and course development work as well as our outreach activities for K-12 STEM groups, further enhancing the broader impacts of this effort.The technical objective of this project is to develop an ultrafast-laser-based optical diagnostic technique capable of measuring chemical species-with initial focus on highly reactive atomic species-in harsh environments without taking in to account complex quenching processes that limit the precision and accuracy of such measurements. Space and time varying concentrations of quenching partners are virtually impossible to quantify in such turbulent flow fields. Furthermore, temperature- and pressure-dependent species-specific quenching cross section data needed for corrections are rather limited and virtually impossible to obtain in many practical situations. In recent years, significant advances have been made in femtosecond-laser-based diagnostic tools for high-repetition-rate imaging of atomic and molecular species in flames and plasmas. However, molecular quenching effects have still prevailed in these diagnostics. In the present work, innovative new nonlinear optical techniques are investigated to elevate such diagnostics to the next level by measuring important atomic and molecular species without the need of quenching corrections. The new diagnostics will be evaluated in high-pressure conditions as well and complex reacting turbulent flow conditions. Subsequently, they will be used to generate critical data sets for chemical kinetics model validation in a selected set of turbulent flames and to characterize a new type of ''wall-less'' reactor designed for chemical kinetics studies.
