Effect of helium dilution on the dynamic stability of lean premixed methane flame in a model gas turbine combustor

Today, where clean, renewable and high efficiency energy production gains importance, methane gas draws attention due to its low carbon content. In this study, flame instability and temperature of methane gas were tested in a premixed model gas turbine combustor at different helium dilution conditions. The burner power was kept constant as 3 kW and the equivalence ratio as 0.7. In addition, a swirl generator with a swirl number of 1 is placed at the burner outlet. The dynamic pressure values of the flame were recorded under external acoustic enforcements at different frequencies applied to the flame and thermo-acoustic combustion instability was interpreted. Methane flame diluted with Helium at 10, 20, 30, 40 and 45 volumetric ratios showed the following results. If helium dilutions of up to 20% did not significantly affect flame instability, instability increased at 30% He. After this critical value, when 45% He dilution was tested, the lowest instability value was determined. In addition, the burner exit temperature of the flame decreased at all helium dilution ratios.