Effects of the equivalence ratio transient durations on selfexcited combustion instability time scales in a single nozzle combustor

Fuel staging is an effective way to attenuate combustion instability in lean, premixed combustion systems. Combustion instability occurs due to the coupling between heat release rate oscillations and combustor acoustics. In our experiments, we seek to understand how transient fuel staging affects the structure and dynamics of a single flame to help inform our previous studies of multi-flame systems. In the current experiments, fuel staging is achieved by changing the equivalence ratio in the nozzle. The equivalence ratio in the nozzle is varied over two different timescales, or transient durations, which are 1 ms and 4 s. For each duration, we also vary the percentage change in the equivalence ratio, with levels of ±3.57% and ±7.14% of the mean equivalence ratio, ψ=0.7. Flame images recorded using CH chemiluminescence imaging are analyzed to show the variations of the phase difference between pressure and heat release oscillations during transients. Phase difference transition behaves similarly in the flame base region but differently in flame/wall interaction region. More similarities between short and long duration transients are observed in combustion instability onset direction than decay direction.