In-situ diagnostics of combustion parameters using laser-induced breakdown spectroscopy

Laser-Induced breakdown spectroscopy is a powerful diagnostic method that can be applied to combustion systems for measurements of fuel-air ratios, fuel composition, and temperature. In this study, we specifically show the application of LIBS for in-situ flame temperature measurements at conditions up to moderately sooting conditions (equivalence ratio of 15 for methane-air flames). Comparisons with existing data obtained from thermocouple exhibit excellent agreement in weakly sooting flames and good agreement at higher equivalence ratios. The deviation at higher equivalence ratios is attributed to signal trapping due to soot and precursor species and also due to increase in hydrogen spectral signal at these conditions. These are factors that can be circumvented and do not preclude application of LIBS to highly sooting flames.