Effect of local flame properties on chemiluminescence-based stoichiometry measurement

•Feasibility of using chemiluminescence for local stoichiometry monitoring is tested.•Non-negligible effect of local conditions on chemiluminescence ratios is found.•The experimental results have been confronted with theoretical calculations.•Both theoretical and experimental results are in qualitative agreement.•Effects observed should be taken into account for the application of the technique.

Spontaneous chemiluminescence emission has been suggested as one of the most promising options for flame stoichiometry monitoring, with particularly interesting application for lean premixed combustors. Most published works are focused on global and time-averaged flame stoichiometry; however, the results reported in previous studies it can be concluded that chemiluminescence measurement could be also valid for local or instantaneous equivalence ratio monitoring. This could enable the development of novel diagnostic techniques with interesting applications in many combustion situations, like the study of thermo-acoustic instabilities. This was the main motivation for this study, focused on analyzing the feasibility of chemiluminescence for space- and/or time-resolved stoichiometry measurements. The results revealed unexpected results, not reported in previous studies, with a non-negligible variation of the relation between chemiluminescence and equivalence ratio that seems to be related to changes in local flame properties such as temperature or composition. This finding has important practical consequences since the chemiluminescence vs. equivalence ratio curves should be carefully verified for each application.