An Experimental Investigation on Flame Pulsation for a Swirl Non-Premixed Combustion

Zhongya Xi,Syed Sabir,Yibo Jiang,Zhongguang Fu,Xiaotian Hu

doi:10.3390/en11071757

Abstract

Flame pulsation has a significant effect on combustion, and understanding its oscillatory behavior is important to the combustion community. An experiment was performed to analyze the pulsation characteristics of a swirl non-premixed flame under various parameters. The results showed that as fuel mass flow rate increased, the puffing frequency increased due to the decreased flame radiation fraction, and the puffing amplitude became smaller resulting in a more stable flame. With an increase in combustor pressure, the flickering frequency declined because of the increasing soot radiation, while the flickering amplitude uniformly increased, leading to more deteriorative flame stability. With an increment in mass flow rate of primary air, the puffing frequency decreased due to the enhanced mixing between fuel and primary air. Also, the puffing amplitude had an oscillating relationship with the mass flow rate of primary air. When the exit velocity of the injector was increased, the flickering frequency diminished nearly linearly because of the improving swirl intensity, and the flickering amplitude was approximately unaffected by injector exit velocity. Moreover, the measured puffing frequencies summarized over all cases varied within the range of 3–22 Hz, the predicted values from theoretical models based on non-swirl flame also fell within this range. The puffing frequency of swirl combustion was more sensitive to the variation in operating conditions than that of non-swirl combustion. Additionally, the obtained correlations indicated that the Strouhal number St was proportional to Fr−1.4 (the Froude number) and Re−2.9 (the Reynolds number), respectively.

Highlights

Turbulent non-premixed flames are widely employed in the majority of practical combustion systems, primarily due to the ease with which such flames can be controlled
Observation of a luminous non-premixed flame indicates that the flame is not in a quiescent state at any time; it exhibits a considerable oscillatory behavior which is often referred as “flame pulsation,” “flame puffing,” or
Kelvin-Helmholtz instability initiates large vortices around the flame surface driven by buoyant force

Summary

Introduction

Turbulent non-premixed flames are widely employed in the majority of practical combustion systems, primarily due to the ease with which such flames can be controlled. Observation of a luminous non-premixed flame indicates that the flame is not in a quiescent state at any time; it exhibits a considerable oscillatory behavior which is often referred as “flame pulsation,” “flame puffing,” or “flame flickering” [1]. Kelvin-Helmholtz instability initiates large vortices around the flame surface driven by buoyant force. These vortices, having convective motion, cause flame pulsation [2]. 501–502, Viskanta, R.; Menguc, M.P. Radiation heat transfer in combustion systems. A.H. Flame radiation in gas turbine combustion chambers.

Methods

Discussion

Conclusion