Effects of Combustor Geometry on the Flowfields and Flame Properties of a Low-Swirl Injector

Abstract

The Low-swirl injector (LSI) is a novel dry-low NOx combustion method that is being developed for gas turbines to burn a variety of gaseous fuels including natural gas, low-Btu fuels, syngases and hydrogen. Its basic principle is described by a top level analytical model that relates the flame position to the flowfield similarity parameters and the turbulent flame speed correlation. The model was based on experimental measurements in open laboratory flames. It has been useful for guiding hardware development. As the LSI is being adapted to different engine configurations, one open question is how the combustor geometry and size affect its basic operating principle. The objective of this paper is to investigate these effects by conducting Particle Image Velocimetry (PIV) measurements in open and enclosed flames produced by a 6.35 cm diameter LSI using two quartz cylinders of 15.5 and 20 cm diameter to simulate the combustor casing. Results from 18 methane-air flames show that the enclosures do not alter the flame properties or the nearfield flow structures. The differences occur mostly in the farfield where the tighter enclosure deters the formation of a weak recirculation zone. The enclosure effects on hydrogen and hydrogen-methane flames were studies using the 20 cm cylinder. The results show that the outer recirculation zone generated at the corner of the dump plane promotes the formation of attached flames. However, the properties and nearfield flow features of the attached flames are similar to those of the lifted flames. At higher stoichiometries, the attached flame collapses to form a compact disc shaped flame that has very different flowfield structures. These results show that the enclosure effects on the LSI are strongly coupled to the fuel type and dump plane geometry but are less dependent on the enclosure size. These observations will provide the basis for developing computational methods that can be used as design tools for LSI adaptation. INTRODUCTIONOur research is motivated by the need of a cost effective, robust, and ultra-low emission combustor for the gas turbines in FutureGen power plant that burns syngases derived from gasification of coal. The objective is to adapt the low-swirl combustion method to these utility size gas turbines that operate on fuels with very high H 2 constituency. Low-swirl combustion is a dry-low-NO x lean premixed combustion method that has been commercialized for industrial heaters. Low-swirl injectors (LSI) have been developed for natural gas industrial turbines (5 -7 MW) in partnership with Solar Turbines of San Diego, California, and for microturbines (100 kW) in partnership with Elliott Energy Systems of Stuart, Florida [1,2].The FutureGen power plant utilizes the Integrated Gasification Combined Cycle (IGCC) approach to produce hydrogen, which is separated from a concentrated CO 2 stream that is then captured for subsequent sequestration. One of its key components is a cost-competitive all-hydrogen fueled turbine with ultra low NO x emission and high eff...

Impact of confinement on flowfield of swirl flow burners

“…However, as stated earlier, the recirculation zone is widened along with an overall increase in strength. These results agree with the findings of Fu et al [8] and Cheng et al [12].…”

“…The swirl burner was confined using a quartz cylinder with a diameter ratio (D q /D b ) of 1.7, where D q is the quartz diameter and D b is the burner diameter, leading to an area ratio of 2.9. This is significantly smaller than values reported in the literature (4 by Archer et al [7] and Fu et al [8], 6 and 9.9 by Cheng et al [12], and 12.25 by Nogenmyr et al [19]). It is to be noted that both the confinement ratio and swirl configuration used here are different than those cited in the above investigations.…”

“…More recently, low swirl burners have been proposed in contrast to high swirl burners due to their benefits in terms of reduced emissions [9,10], stabilization of planar flames without heat losses or boundary effect [11], and low pressure drop. In another study, Cheng et al investigated the flowfield of low swirl injector [12]. They outlined the difference between unconfined and confined cases under reacting and non-reacting conditions with methane and hydrogen as the fuel with confinement ratios of 3 and 2.44:1.…”

“…They demonstrated that enclosure increases the central recirculation zone under non-reacting conditions. On the other hand, for methane flames, enclosure had minimal effect at the 3:1 confinement ratio; however, the smaller confinement did not generate central flow recirculation [12]. Other researchers examined the flowfield, temperatures, and species distribution within swirl flames [13][14][15][16].…”

Enabling Advanced Modeling and Simulations for Fuel-Flexible Combustors

“…Full details about the experimental configuration can be found in Ref. [22]. Figure 12 shows the instantaneous velocity and vorticity profiles in this configuration.…”