A review of laser-induced breakdown spectroscopy and spontaneous emission techniques in monitoring thermal conversion of fuels

Thermal conversion, such as combustion, is the basic utilization of fuel energy. In-situ detection of key parameters (e.g., components of fuel and combustion products, temperature, and pressure) is critical for improving the fuel utilization and the efficiency of thermal conversion equipment as well as to gain a full understanding of the mechanism of the thermal conversion process. Laser-induced breakdown spectroscopy (LIBS) has been verified to be applicable in the relevant industrial environment. In addition, combustion inherently comes with spontaneous emission, which contains important information about the process. This review discusses the application of atomic emission spectroscopy for monitoring the fuel thermal conversion process, including the characterization of raw energy materials (coal, biomass) before combustion, during the fuel combustion process (flame) and after combustion (fly ash). The first section is focused on LIBS for the analysis of raw energy materials in different forms like rock, pellets and particle flow. A series of online application instruments for energy materials properties analysis have been developed. The second section is focused on the characterization of the fuel combustion process with the use of LIBS and spontaneous emission. The third section is on unburned carbon detection in fly ash with LIBS. Furthermore, application prospects of LIBS and spontaneous emission techniques in the energy conversion field are analyzed and discussed to provide a reference for the development of technology.