Development of Laser-induced Breakdown Spectroscopy for Multiple Parameter Measurements in Sooting Flames

• Applicant: Professor Dr.-Ing. Johannes Kiefer
• Subject Area: Technical Thermodynamics
• Term: from 2016 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 299488043

The aim of the project is to develop laser-induced breakdown spectroscopy (LIBS) as a tool for the experimental determination of multiple parameters such as temperature and chemical composition in sooting flames. When LIBS is applied to aerosols like sooting flames, there are a number of interfering signals. The presence of nanoparticles and their aggregates causes significant elastic scattering of laser light via Mie- and Rayleigh scattering. In addition, the particles may absorb the laser radiation and thus be heated to high temperature, which leads to the emission of laser-induced incandescence (LII). Furthermore, there can be fluorescence signals of combustion intermediates and laser-generated species. Hence, in order to make LIBS a suitable diagnostic tool for the investigation of sooting flames, a strategy must be developed that allows distinguishing the LIBS signal from the inferences. For this purpose, various experimental approaches and data evaluation methods need to be combined and tested systematically. Experimentally, the recording of time-integrated and time-resolved signals will be compared. Another challenge for LIBS in aerosols is that the particles reduce the breakdown threshold, i.e. the minimum laser pulse energy required to induce a breakdown. Therefore, the influence of the particles on the plasma formation and behavior need to be understood and predictable in order to develop a reproducible LIBS technique for sooting flames. This project aims at developing a fundamental understanding of the involved processes that are relevant for using LIBS as an analytical method in sooting flames. A predictive model will be developed from systematic experiments and theoretical considerations. This will form the basis for establishing LIBS as a tool for multiple parameter measurements in sooting flames. Within this project, a suitable combination of an experimental method and a strategy for data evaluation will be developed.

• DFG Programme: Research Grants