Flame chemiluminescence in premixed combustion of hydrogen-enriched fuels

•Using chemiluminescence for stoichiometry (ER) monitoring in syngas flames.•Different hydrogen enriched fuels were tested.•Results revealed that the ratio OH*/CH* may not be applied under certain conditions.•The ratio OH∗/CO2* was suggested as a promising alternative.•Numerical predictions revealed influence of ER and H2 addition on combustion regime.

The growing interest in the use of syngas, produced from gasification of a number of fuels such as coal, biomass or waste, has increased the need of developing new strategies of flame control and monitoring in order to ensure a quiet and efficient combustion in the current combustion systems, which had been optimized for conventional fuels.Chemiluminescence emission from flames has been suggested as a promising alternative for stoichiometry monitoring in methane or natural gas premixed flames but its use in syngas flames is clearly less tested. Therefore, the main motivation of this study is analyzing the possibility of using chemiluminescence-based techniques for stoichiometry estimation in flames with different hydrogen-enriched fuels, which can be considered as a first approach for a wide range of syngas compositions. The results revealed that the ratio OH*/CH*, which had been widely demonstrated to be the best option for methane, may not be suitable to monitor flames with high hydrogen content at certain operating ranges, where the ratio OH∗/CO2* is suggested as a promising alternative.In addition, the numerical predictions seemed to indicate that the change in the trends observed for different equivalence ratio ranges and fuel compositions may be associated with the existence of different combustion regimes. To the authors' knowledge, this is a novel finding that has not been explored before and could have important practical consequences for the application of the technique in real combustors.