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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

# Investigation of Lean Premixed Swirl-Stabilized Hydrogen Burner With Axial Air Injection Using OH-PLIF Imaging

[+] Author and Article Information
Thoralf G. Reichel

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany
e-mail: thoralf.reichel@tu-berlin.de

Katharina Goeckeler, Oliver Paschereit

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 13, 2015; final manuscript received July 20, 2015; published online September 18, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(11), 111513 (Sep 18, 2015) (10 pages) Paper No: GTP-15-1263; doi: 10.1115/1.4031181 History: Received July 13, 2015; Revised July 20, 2015

## Abstract

In the context of lean premixed combustion, the prevention of upstream flame propagation in the premixing zone, referred to as flashback (FB), is a crucial challenge related to the application of hydrogen as a fuel for gas turbines. The location of flame anchoring and its impact on FB tendencies in a technically premixed, swirl-stabilized hydrogen burner are investigated experimentally at atmospheric pressure conditions using planar laser-induced fluorescence of hydroxyl radicals (OH-PLIF). The inlet conditions are systematically varied with respect to equivalence ratio $(ϕ=0.2−1.0)$, bulk air velocity u0 = 30–90 m/s, and burner preheat temperature ranging from 300 K to 700 K. The burner is mounted in an atmospheric combustion test rig, firing at a power of up to 220 kW into a 105 mm diameter quartz cylinder, which provides optical access to the flame region. The experiments were performed using an in-house burner design that previously proved to be highly resistant against FB occurrence by applying the axial air injection strategy. Axial air injection constitutes a nonswirling air jet on the central axis of the radial swirl generator. While a high rate of axial air injection yields excellent FB resistance, reduced rates of air injection are utilized to trigger FB, which allowed to investigate the near FB flame behavior. Results show that both, fuel momentum of hydrogen and axial air injection, alter the isothermal flow field as they cause a downstream shift of vortex breakdown and, thus, the axial flame front location. Such a shift is proven beneficial for FB resistance from the recorded FB limits. This effect was quantified by applying an edge detection algorithm to the OH-PLIF images, in order to extract the location of maximum flame front probability xF. By these means, it was revealed that for hydrogen xF is shifted downstream with increasing equivalence ratio due to the added momentum of the fuel flow, superseding any parallel augmentation in the turbulent flame speed. The parameter xF is identified to be governed by J, the momentum ratio between fuel and air flow, over a wide range of inlet conditions. These results contribute to the understanding of the sensitivity of FB to changes in the flow field, stemming from geometry changes or specific fuel properties.

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## Figures

Fig. 1

Stability limits (from Ref. [13]) for χ = 12.5% and χ = 7.5%; both configurations operated at ϕ = 1 without FB (symbol × , ϕ > 1 not tested). Hence, only the lower stability limits are displayed.

Fig. 2

Bulk outlet velocity u0(ϕ), top, and momentum ratio J, bottom, at constant air mass flow m˙air with respect to varied equivalence ratio ϕ and ratio of inlet air to fuel temperature (Tin/Tfuel) for hydrogen, left, and methane, right

Fig. 3

Schematic of burner model, indicating different volume flow pathways through swirl generator or axial injection

Fig. 4

Experimental setup for OH-PLIF measurements in atmospheric combustion test rig

Fig. 5

Isothermal flow field in the absence (χ = 0%, left column) and presence of a medium (χ = 7.5%, center column) and high (χ = 12.5%, right column) amount of axial air injection. Additionally, the effect of injected fuel is presented at J = 3 (center row) and J = 6 (bottom row); (Re = 40,000, S = 0.9, and u0 = const.); solid lines indicating u/u0 = 0.

Fig. 6

Extraction method for axial location of maximum flame front probability xF from a series of OH PLIF snapshots (Tin = 450 K, u0 = 70 m/s, and ϕ=0.3)

Fig. 7

Mean OH signal probability (top row) and instant OH-PLIF images (bottom row) in the presence of high axial air injection (χ = 12.5%) recorded at Tin = 453 K and u0 = 70 m/s

Fig. 8

Mean OH signal probability (top row) and instant OH-PLIF images (bottom row) in the presence of medium axial air injection (χ = 7.5%) recorded at Tin = 453 K and u0 = 70 m/s

Fig. 9

Location of maximum flame front likelihood xF over equivalence ratio ϕ for varied air preheat temperatures Tin for methane (left, χ = 12.5%) and hydrogen (center, χ = 12.5% and right χ = 7.5%); all points recorded at a constant bulk air velocity u0 = 70 m/s

Fig. 10

Location of maximum flame front likelihood xF over bulk air velocity u0 for varied air preheat temperatures Tin for hydrogen at χ = 12.5% for ϕ=0.4 (left) and ϕ=0.6 (right)

Fig. 11

Measured (symbols) and modeled (lines) fuel temperature as a function of air preheat temperature Tin and equivalence ratio at constant u0 = 70 m/s

Fig. 12

xF over J with varied Tin and ϕ for hydrogen at χ = 7.5% (solid), χ = 12.5% (dotted), and methane at χ = 12.5% (dashed line)

Fig. 13

Location of maximum flame front likelihood xF over Reynolds number, varying Tin (circle color) and ϕ=0.2−1.0 (circle diameter) yields different levels of momentum ratio J, recorded for hydrogen at χ = 12.5%

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