Experimental Investigation of the Effects of Central Fuel Injectors on Premixed Swirling Flames

Abstract

The demand for alternative fuels has increased significantly during the previous decades in order to reduce pollutants and increase the amount of energy that can be generated from nonfossil fuels. However, the use of new fuels faces many issues especially the problem of stability of operation which sometimes can cause severe damages to the system hardware. Thus the development of flexible combustion systems for gas turbines becomes urgent in order to achieve high reliability with these new sources of energy.Swirl stabilized combustion is the most widely spread deployed technology used to stabilize and control combustion in gas turbines and numerous other systems. However, the interaction of the swirling flows with the burner geometries is very complex and it has been proved that any change in the burner geometry can affect the flow field inside the combustion chamber, close to the burner mouth and downstream the combustion zone. Most burners are generally provided with a diffusive injector that centrally delivers well-known fuels allowing the stabilization of the system previous to entirely premixed conditions. Moreover, the injector anchors the central recirculation zone formed downstream of the nozzle. However, the use of injectors can also affect the stability limits of the system, especially the propagation of flashback through changes of shape of the shear layer since other structures such as the Combustion Induced Vortex Breakdown are suppressed due to the presence of this central body. However, the characterization of the flow and its impacts on the propagation of these and other flashback structures using different injectors has been briefly documented.

Experimental Study of the Effect of Swirl Number and Bluff Body Size on the Stability Map of Premixed LPG Flames in a Tangential Swirl Burner

“…However, reducing the annular passage area increases the momentum of the incoming mixture and stabilizes the CRZ more upstream, near the burner outlet. Therefore, increasing B led to an increase in the flow velocity of the unburned mixture, which led to shifting the stagnation point of the flow downstream and thus better resistance to flashback, and this behavior is consistent with [38].…”

“…Also, increasing the annular passage area leads to a decrease in the flow velocity of the fresh mixture, which is one of the reasons for the increase in the flashback propensity. On the other hand, for all inlet tangential velocities, it was noted that with the small diameter of the injector, the CRZ surrounds the center fuel injector and extends towards the base plate of the burner, causing a significant increase in the temperature around the injector and thus increasing the levels of pollutants and reducing the injector life [38].…”