1. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 Increase of both, (a) bulk outlet velocity u0(φ) and (b) momentum ratio J, with equivalence ratio strongly depends on ratio of inlet air to fuel temperature (T in /T fuel ) Figure Legend:

2. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 Schematic of burner model, indicating different volume flow pathways through swirl generator or axial injection Figure Legend:

3. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 Experimental setup for simultaneous PIV and OH* measurements in atmospheric combustion test rig Figure Legend:

4. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 Velocity vectors superimposed on normalized mean axial velocity of the isothermal flow field in the (a) absence (D or = 0 mm) and (b) presence of a medium (D or = 8.0 mm), and (c) high (D or = 8.8 mm) amount of axial air injection (long mixing tube; S = 0.9), solid lines indicating zero axial velocity Figure Legend:

5. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 Histogram of axial velocity at (x/D = 0.1, r/D = 0) for isothermal conditions in the absence (D or = 0 mm) and presence of a medium (D or = 8.0 mm) and high (D or = 8.8 mm) amount of axial air injection (Re = 68,000) Figure Legend:

6. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 Stability limits for varied air mass flows at two inlet temperatures; configurations 1–4 operated at stoichiometric conditions without flashback (symbol ×, not tested above stoichiometric). Hence, only the lower stability limits are displayed for each configuration. Figure Legend:

7. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 Impact of increased equivalence ratio for the reacting flow (m· = 180 kg/h, t in = 450 k) for a high ((a)–(c), φ=0, 0.4, and 0.8) and medium ((d)–(f), φ=0, 0.4, and 0.6) amount of axial air injection. Solid lines indicate zero axial velocity. Figure Legend:

8. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 Histogram of axial velocity at (x/D = 0.1, r/D = 0) revealing impact of fuel momentum in the presence of high (D or = 8.8 mm) amount of axial air injection (Re = 75,000) Figure Legend:

9. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 Observed VB types during PIV measurements of configurations 3 and 4 transferred to schematic in Ref. [18], in order to explain difference in character of axial air injection (χ ↑) and fuel momentum (φ↑) Figure Legend:

10. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 Flame probability indicating the likelihood of the flame to appear in a certain region, hence, allowing to determine the upstream flame shape (Re = 75,000) Figure Legend:

11. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 ABEL-deconvoluted OH* images normalized to the maximum intensity of the image at φ=0.8 (Re = 75,000) Figure Legend:

12. Date of download: 11/12/2016 Copyright © ASME. All rights reserved. From: Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection J. Eng. Gas Turbines Power. 2015;137(7):071503-071503-9. doi:10.1115/1.4029119 NO x emissions (dry) over calculated adiabatic flame temperature for high axial air injection Figure Legend: