Research progress of laser photofragmentation-fragment detection techniques in combustion diagnostics

Combustion remains the primary process for energy supply in nowadays society. With the emerging of low-carbon fuels alongside traditional fossil fuels, the increased complexity of thermal-chemical conversion processes call for more accurate diagnostic tools. Compared to traditional offline measurement techniques which are often insufficient in providing precise information, advanced laser diagnostics techniques are increasingly important for providing in-situ measurements in combustion processes due to their high sensitivity, selectivity, and non-intrusive features. In this paper, the developments and applications of laser diagnostics techniques based on the Laser Photofragmentation and Fragment Detection (PF-FD) strategy in combustion are reviewed. First, the motivation for this paper is briefly discussed, as well as the advantages of PF-FD techniques in combustion diagnostics. Second, the recent PF-FD techniques applied in combustion diagnostics are summarized, including Photofragmentation and Prompt Emission (PF-PE), Photofragmentation and Laser Induced Fluorescence (PF-LIF), and Photofragmentation and Laser Absorption Spectroscopy (PF-LAS). The primary focus is on the measurements of species concentrations, velocity/temperature fields, and flame structure using PF-FD, involving hydrocarbons, H2O2/HO2/H2O, ozone, nitrogenous compounds, and alkali metal/heavy metal compounds. Finally, a comparison and outlook of different PF-FD methods in combustion diagnostics, both in the laboratory and the field, are presented.