Fuel effects on a low-swirl injector for lean premixed gas turbines

Littlejohn, David; Cheng, R.K.

doi:10.1016/j.proci.2006.07.146

Cited by 69 publications

(56 citation statements)

References 16 publications

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“…Burning under lean conditions reduces the exhaust gas temperatures, and consequently, thermal NOx emissions. Low-swirl burner technology, introduced by [1] as a tool for studying the fundamental properties of lean premixed turbulent flames has proven to be an effective stabilization mechanism for a wide range of fuels, see [2] and [3]. However, high-swirl injectors, often used in gas turbines, can generate much higher levels of turbulence.…”

Section: Introductionmentioning

confidence: 99%

Lewis number effects in distributed flames

Aspden

Day

Bell

2011

Proceedings of the Combustion Institute

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Recent computational studies have simulated a mode of distributed premixed combustion where turbulent mixing plays a significant role in the transport of mass and heat near the reaction zone. Under these conditions, molecular transport processes play a correspondingly smaller role. A consequence of burning in this regime is that a change in the gas mixture composition can occur within the flame zone, which modifies the burning rate. The composition depends on the Lewis number (ratio of molecular heat to mass diffusivity), and so the response to the transition to distributed burning will be different for fuels with different Lewis numbers. In this paper, we examine the role of Lewis number on flames in the distributed burning regime. We use high-resolution three-dimensional flame simulations with detailed transport models to explore the turbulent combustion of a range of fuels, specifically lean premixed hydrogen, methane and propane mixtures. The response of the burning rate is found to be more pronounced in hydrogen than in the other fuels.

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Section: Introductionmentioning

confidence: 99%

Lewis number effects in distributed flames

Aspden

Day

Bell

2011

Proceedings of the Combustion Institute

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“…Cellular burning patterns have been observed experimentally in lean H2/O2 mixtures by many researchers (see, for example, [3] and [4]). Low-swirl burner technology, introduced by [5], has proven to be an effective stabilization mechanism for a wide range of fuels, including H2, see [6] and [7]. Turbulent lean H2 flames at moderate turbulence levels have also been studied computationally, both in idealized configurations by [8][9][10], and in a lowswirl burner configuration [11].…”

Section: Introductionmentioning

confidence: 99%

Characterization of low Lewis number flames

Aspden

Day

Bell

2011

Proceedings of the Combustion Institute

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A recent numerical study of turbulence-flame interactions in lean premixed hydrogen, where the Lewis number was approximately 0.36, observed that flames at different equivalence ratios presented significantly different behavior despite having the same Karlovitz and Damköhler numbers. This differing behavior is due to the thermodiffusively-unstable nature of low Lewis number flames. In more than one dimension, differential diffusion focuses fuel into hot regions increasing the local burning rate, which was found to affect the leaner hydrogen flames more significantly. Ultimately, this difference between idealized flat flames and freely-propagating flames undermines the characterization of turbulent flames through Karlovitz and Damköhler numbers based on flat laminar quantities. This paper considers refining the definitions of these dimensionless numbers by replacing the flat laminar flame values with freely-propagating values. In particular, we perform three-dimensional simulations of freely-propagating flames over a range of equivalence ratios, and use data from those simulations to define modified Karlovitz and Damkölher numbers. We then perform a series of turbulent flame simulations that show that defining Karlovitz and Damkölher numbers based on the freely-propagating flames effectively eliminates dependence on equivalence ratio.

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“…Analyses of the velocity measurements show that the LSI flowfield exhibits self-similarity behavior. Two parameters deduced from the centerline velocity profiles are invoked to characterize self-similar behavior [13,14]. They are the virtual origin of the divergent flow, x 0, and the non-dimensional axial aerodynamic stretch rate, a x .…”

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confidence: 99%

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

Cheng

Littlejohn

2008

Volume 3: Combustion, Fuels and Emissions, Parts a and B

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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...

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Fuel effects on a low-swirl injector for lean premixed gas turbines

Cited by 69 publications

References 16 publications

Lewis number effects in distributed flames

Lewis number effects in distributed flames

Characterization of low Lewis number flames

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

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