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

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.

Effects of steam addition and/or injection on the combustion characteristics: A review

“…Using this system could alleviate existing concerns regarding flame flashback. The overall amount of air passing through the system was kept constant during the experiment, and the value of this parameter was obtained from the velocity field measurements conducted in previous studies [79]. The tests in this study were conducted using a high-pressure test rig in a high-pressure combustor in Stuttgart, Germany.…”

Emissions of a Wet Premixed Flame of Natural Gas and a Mixture With Hydrogen at High Pressure

“…Instead, the pressure drop of the two passages, swirl generator and central orifice, is adjusted by changing their surface area. This air proportion was kept constant throughout the experiments presented in the current work, and it was determined from previous velocity field measurements [15]. Fuel is injected into the mixing tube through 16 injection holes located around the axial air injection orifice.…”

“…The combustion system of the current work also uses axial air and fuel injection to control the position of the vortex breakdown zone. A thorough presentation of the system design, its stability maps and the respective emissions in experiments with pure hydrogen at atmospheric pressure have been presented in the works of Reichel et al [14,15]. Kuhn et al [16] extended this work by performing experiments in a very wide range of conditions, ranging from pure hydrogen to steam diluted natural gas.…”

Numerical analysis supported with experimental measurements of premixed oxy‐propane flames in a fuel‐flex gas turbine combustor

“…Among these, swirl-stabilized burners have been investigated the most for oxycombustion application. [13][14][15][16][17][18] Moreover, oxy-combustion of various fuels (eg, methane, [19][20][21] propane, [22][23][24] syngas, [25][26][27] ammonia, [28][29][30] and hydrogen [31][32][33] ) at varying combustion parameters, such as equivalence ratio (ϕ), oxygen fraction (OF), adiabatic flame temperature (T ad ), and flame speed (FS), has been examined as well. Most research is focused on methane, with fewer studies examining propane.…”