Influence of staged-air flow on flow characteristics in a scale model of a down-fired utility boiler with swirl burners: An experimental study

► We conduct cold airflow experiments in the small-scale furnace of a down-fired boiler. ► We study influence of staged-air flow on flow characteristics of the boiler in this model. ► The flame reach of the downward airflow was decreased with the ratio increased. ► A shallower reach is accompanied by a weaker mixing of vent and staged-air.