Flashback in a Swirl Burner With Cylindrical Premixing Zone

Abstract

Flame flashback from the combustion chamber into the mixing zone is one of the inherent problems of lean premixed combustion and essentially determines the reliability of low NOx burners. Generally, flashback can be initiated by one of the following four phenomena: flashback due to the conditions in the boundary layer, flashback due to turbulent flame propagation in the core flow, flashback induced by combustion instabilities and flashback caused by combustion induced vortex breakdown. In this study, flashback in a swirling tubular flow was investigated. In order to draw maximum benefit from the tests with respect to the application in gas turbines, the radial distribution of the axial and circumferential momentum in the tube was selected such that the typical character of a flow in mixing zones of premix burners without centerbody was obtained. A single burner test rig has been designed to provoke flashback with the preheating temperature, the equivalence ratio and the mean flow rate being the influencing parameters. The flame position within the mixing section is detected by a special optical flame sensor array, which allows the control of the experiment and furthermore the triggering of the measurement techniques. The burning velocity of the fuel has been varied by using natural gas or hydrogen. The characteristics of the flashback, the unsteady swirling flow during the flame propagation, the flame dynamics and the reaction zones have been investigated by applying high-speed video recordings, the laser Doppler anemometry and the laser induced fluorescence. The presented results show that a combustion induced vortex breakdown is the dominating mechanism of the observed flashback. This mechanism is very sensitive to the momentum distribution in the vortex core. By adding axial momentum around the mixing tube axis, the circumferential velocity gradient is reduced and flashback can be prevented.

Laboratory investigations of a low-swirl injector with H2 and CH4 at gas turbine conditions

“…To characterize the difference in their flashback behavior, the quenching factor, C quench , of Fritz et al [20] was used. These authors show that the Peclet number at φ FB …”

Generation of Adverse Pressure Gradient in the Circumferential Flashback of a Premixed Flame

“…Amongst them are the existence of an adverse pressure gradient and sudden expansions in the flow. As most swirling flames may include these features, analogies were proposed between vortex breakdown in isothermal flows and enhanced flame propagation in vortex tubes [36]. In these flows, a high pressure point along the axis of rotation brings the fluid to rest which is, subsequently, followed by the formation of a recirculation zone [36].…”

“…In an experimental and theoretical work Fritz et al [36] studied the flashback of a flame purely stabilised by vortex breakdown. These authors demonstrated that the swirling flow field breaks down prior to flashback and therefore encourages upstream propagation of the flame [36].…”

“…Vortex breakdown in reactive flows has been investigated in a number of works [36][37][38][39][40][41][42].…”

LES of Premixed Flame Propagation in a Free Straight Vortex

“…One example is the combustion chamber of gas turbines [10,11,23]. Due to progressively more demanding emission limits, stationary gas turbines utilize premixed combustion chambers.…”