A swirling burner with a variable inner secondary air (ISA) flaring angle β is proposed and a laboratory scale opposed-firing furnace is built. Temperature distribution and NOx emission are designedly measured. The combustion characteristics affected by variable β are experimentally evaluated from ignition and burnout data. https://safeersappliancers.shop/product-category/aeg-dbe5961hg-90-cm-chimney-cooker-hood-stainless-steel/