Flame stabilization and pollutant emissions from a H 2 /air dual swirl coaxial injector at elevated pressure
Résumé
Understanding mechanisms controlling flame stabilization and pollutant emissions in swirled hydrogen flames at elevated pressures is crucial for advancing hydrogen-powered gas turbines. In this work, a single sector model gas turbine combustor operated with a coaxial dual swirl H 2 /air injector is installed in a high pressure test rig equipped with optical access. Flame stabilization and pollutant emissions of NO, NO 2 , and N 2 O are investigated at atmospheric injection temperature across a wide range of air and hydrogen injection velocities and operating pressures up to 8 bars. Two stabilization modes are identified: flames anchored to the hydrogen injector nozzle and flames lifted above the coaxial injector. It is shown that the air injection velocity required to lift the flame from the hydrogen injector rim increases with rising hydrogen velocity or pressure. However, with the current burner design, the lift-off air velocity reaches a plateau beyond 4 bars, regardless of the hydrogen inlet velocity. N 2 O emissions remain negligible for all operating conditions explored. Except at very lean operating conditions with global equivalence ratios below 0.3, NO 2 emissions are negligible too. It is finally shown that NO emissions scale with the adiabatic flame temperature, residence time in the flame volume, and pressure and that lifted flames typically yield lower NO emissions than anchored flames. The observations presented in this study help identifying critical flow parameters and lay solid foundations for the development of swirled hydrogen burners at elevated pressures.
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