Probing the equivalence ratio in partially premixed flames by combining optical techniques and modeling results

Chemiluminescence and laser-induced breakdown spectroscopy (LIBS) measurements have been carried out in laminar ethylene/air partially premixed flames for real-time local equivalence ratio monitoring. OH* and CH* chemiluminescence measurements have been performed in the region where combustion processes mainly occur. Using LIBS measurements, the hydrogen to oxygen emission signal ratio has been obtained as an indicator of the fuel to air ratio and consequently of the mixing processes. Through a calibration procedure performed in nitrogen-diluted ethylene/air premixed flames of known equivalence ratio, the local values of the equivalence ratio have been derived in the flames under analysis. Target flames, proposed in the framework of the International Sooting Flame (ISF) workshop, have been investigated along the radius at different heights above the burner. Correspondingly, chemical kinetic modeling analysis has been performed and the results were compared with the experimental data in order to cross-check the reliability of both experimental techniques and modeling approach.