Significant progress has been made in recent years to understand flame flashback. However, more validation is needed especially at gas turbine relevant conditions, i.e., at high pressures and high Reynolds numbers \[1\]. Furthermore, the effect of swirl on boundary layer flashback is not fully understood despite its relevance for real swirl burners \[2\].

For this reason, a new canonical swirl burner has been designed and incorporated in our high pressure test rig. The burner features an axial swirler and a cylindrical center body. The mixing tube is made of fused silica to provide optical access to the premix section. The burner is similar to the one used in \[2\], but has a smaller swirl number (about 0.7) and a smaller cross-sectional area. Since the wall temperature is a crucial parameter for quantitative flashback limit measurements \[1\], the center body is equipped with thermocouples to monitor its temperature. Furthermore, the center body is equipped with an internal oil circuit, which allows the wall to be temperature controlled by a combined cooling-heating system. Flashback is triggered by increasing the equivalence ratio for a given pressure, preheat temperature, bulk flow velocity and hydrogen volume fraction.

For this first study, flashback limits have been measured for a wide range of conditions including pressures up 7.5 bar, preheat temperatures up to 300°C, bulk flow velocities in the premix section up to 30 m/s and hydrogen-methane mixtures with up to 100% hydrogen. Flashback limits will be presented and analyzed in detail. Results show that the flashback propensity increases strongly with an increase in pressure but levels off already at about 3 bar. Results further show that the increase in flashback propensity with an increase in preheat temperature is not as strong as one would expect based on the effect of preheat temperature on the flame speed and quenching distance. Furthermore, increasing the bulk flow velocity still has a noticeable effect on decreasing the flashback propensity for intermediate hydrogen contents (about 50 to 85% H~2~ by volume). Chemiluminescence images of the flame during flashback, which propagates along the center body wall, have been recorded at kilohertz-rate and the pathway of the flame during flashback will be discussed.

 

References:

\[1\]    Kalantari, A., & McDonell, V. (2017). Boundary layer flashback of non-swirling premixed flames: Mechanisms, fundamental research, and recent advances. *Progress in Energy and Combustion Science*, *61*, 249–292.

\[2\]    Ebi, D., & Clemens, N. T. (2016). Experimental investigation of upstream flame propagation during boundary layer flashback of swirl flames. *Combustion and Flame*, *168*, 39–52.


Boundary Layer Flashback Limits of Hydrogen-Methane-Air Flames in a Generic Swirl Burner at Gas Turbine Relevant Conditions

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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