The Effect of Inner Secondary Air on the Flow Field of a Swirl Burner

Swirl burner is widely used for coal combustion in boilers. In many swirl burners, the secondary air is divided into two branches, namely inner secondary air (ISA) and outer secondary air (OSA). This paper presents a thorough study on the affecting mechanism of the ISA on the burner flow field via a cold state experiment and a hot state simulation. It is found that, the variation of ISA blade angle has a broad influence on the flow field. As the ISA blade angle increases, the ISA could be mixed earlier with the primary air, which benefits the air stage combustion; besides, its stronger annular jet flow stiffness is good for the entrainment of primary air. The increment of ISA blade angle also increases the annular jet flow stiffness, reduces the main flame recirculation (MFR), and might also move its away from the burner exit in some extent.