Development of a Vane Swirler for Use in a Low NOx Weak Swirl Burner

This paper describes the continuing development of the Weak-Swirl Burner (WSB) for use in low NOx applications. Weak-swirl is a unique method for stabilizing lean-burning, premixed combustion as the flame is stabilized by flow divergence, not through recirculation as is commonly seen in nonpremixed industrial burners. Earlier versions of the WSB used a tangential airjet swirler that offers flexibility for determining the range of operation and evaluating the performance of the WSB. Though common in large applications, air swirler may not be amenable to small and medium-size appliances. To reduce manufacturing costs and burner complexity, we have developed a fixed vane swirler to replace the airjet swirler in the WSB. This paper describes the operating characteristics and key design parameters of the vane swirler. A new expression for determining swirl number intensity is developed. Testing of a laboratory water heater fitted with a WSB with the new vane-swirler shows 0 < NO < 20 ng/J, 10 < CO < 70 ppm, and thermal efficiencies ~ 78% over the lean burning range of 0.70 < $ < 0.90. The continuous firing rate is robust for a 53 mm vane-swirled WSB, with initial tests ranging from 40,000 to 400,000 Btu/hr. for 0.60 < $ < 1.0. Successful development of the new vane swirler demonstrates that the low emission WSB is adaptable to a wide variety of industrial applications.