Experimental investigation on the influence of central airflow on swirl combustion stability and flame shape
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Experimental investigation on the influence of central airflow on swirl combustion stability and flame shape Linyuan Huang1,2 · Changchun Liu1,2 · Tiandiao Deng1,2 · Hua Jiang1,2 · Pengzhi Wu1,2 Received: 3 June 2020 / Accepted: 5 November 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Central airflow has been widely used to improve the performance of swirl burners in engineering applications. This paper reports an experimental investigation on the effects of such airflow on the combustion stability and shape of swirl flames. The results show that, for a low equivalence ratio, central airflow changes the flame shape from an “inverted cone” to a “rectangle” and significantly increases the flame height. Raising the speed of the central airflow increases the maximum temperature on the central axis of the swirl flame because the airflow enhances the upward momentum of the fuel. By contrast, for a high equivalence ratio, the swirl flame is prone to liftoff owing to the influence of the central airflow on the axial momentum of the fuel. In this case, increasing the fuel flow causes the swirl-flame blowout limit to increase and then decrease. This limit for different equivalence ratios is well described by dimensionless function. These findings will provide an important reference for the design of safe and high-performance swirl burners. Keywords Swirl combustion · Central airflow · Equivalence ratio · Flame temperature · Blowout limit List of symbols At Total area of tangential air inlet (mm2) D Ratio of vertical flowing air momentum to swirl air momentum H Flame height (cm) L Center axis distance (cm) m1 Central air mass flow (kg s−1) m2 Fuel mass flow (kg s−1) m3 Swirl air mass flow (kg s−1) mɵ Tangential mass flow (kg s−1) mA Axial mass flow (kg s−1) Pf Combustion power (kW) Qc Center airflow rate (L min−1) r0 Cross section radius of swirl generation chamber (mm) R Nozzle radius (mm) S Swirl strength T Flame temperature (°C) v1 Central air velocity (m s−1) * Changchun Liu [email protected] 1
School of Safety Science and Engineering, Xi’an University of Science and Technology, Xi’an 710054, China
Shaanxi Engineering Research Center for Industrial Process Safety and Emergency Rescue, Xi’an 710054, China
2
v2 Fuel flow rate (m s−1) v3 Swirl airflow rate (m s−1) Greek symbols δ Dimensionless number of combinations φ Equivalence ratio
Introduction Swirl combustion offers good diffusivity, entrainment ability and premixing ability and is often used in gas turbine combustion chambers, ramjets, rocket engines and industrial furnaces [1, 2]. However, the large amount of thermal NOx generated in the swirl combustion process can cause serious damage to the environment [3]. Moreover, it is extremely difficult to control the size of the swirl flames in this process [4]. In recent years, researchers have found that increasing central wind [5] in some industrial swirl burners can reduce NOx emissions [6]. Therefore, to improve the stability of industrial burners and optimize burne
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