METHANE-AIR FLAMES; DIFFUSION FLAMES; CH-ASTERISK; OH-ASTERISK; SOOT; DIAGNOSTICS; EMISSION; FRACTION; MIXTURE; ETHANE

Real-time monitoring of the local equivalence ratio is of primary importance for combustion efficiency improvement. Chemiluminescence and laser-inducedbreakdown spectroscopy (LIBS) measurements can be powerful tools for sensing the equivalence ratio. Radicals, such as OH*, CH*, and C-2*, are formed within the flame front, and consequently, the related chemiluminescence emission can be considered as a marker to follow the evolution of combustion processes. From LIBS measurements, the ratio of two characteristic spectral lines of fuel (H) and oxidizer (0) is related to the equivalence ratio. In this work, LIBS measurements have been carried out in premixed flames of known equivalence ratio for calibration purposes. Then, the application to non-premixed flames has been performed to evaluate the local equivalence ratio. Chemiluminescence emission spectra have also been collected, and the values of OH*, CH*, and C-2* have been properly evaluated, taking into account the contribution of CO2* broad band emission. A methane co-flow diffusion flame has been investigated along the centerline as well as at three cross sections, and the local equivalence ratio profiles obtained by LIBS have been compared to CH* chemiluminescence profiles. Finally, the experimental data obtained were compared to the results of a detailed chemical kinetic model.