Experimental characterisation of flows in the model of a strongly swirling combustor

The control of NO_x production in a combustion chamber requires not only monitoring the nitrogen oxide emissions or, more easily, other variables correlated to it, but also monitoring flame stability and mixture formation by means of probes or optical systems. To investigate this subject, a research project has been started with the design of a multi-task test bench equipped with specific diagnostic instruments and devices that, after proper adaptation, could become idoneous to monitor and control the combustion processes. The present paper is concerned with the preliminary characterisation of a gaseous swirl burner, which can be operated with different transverse fuel injection typologies. It has been inserted in a general purpose combustion chamber with the possibility of applying different optical techniques, such as LDP and LS. The main purpose of the research project was to develop diagnostic techniques and control methodologies which could be implemented in industrial combustion systems to achieve better fluidynamic stability, improved performances and reduced pollutant emissions. The results refer to the preliminary characterisation, under isothermal operating conditions, of the fuel/air mixing in the region near the exit from the burner-quarl. From analysis of digital images and velocity distributions it was found that counter-swirl and co-swirl injection modes seem more efficient in mixing promotion. As a conclusion, possible explanations are given as well as suggestions for future more detailed investigations