Generation of Low-Frequency Alternative Flame Behaviors in a Lean Premixed Combustor

Abstract

Combustion instability causes severe problems, such as fatal damage to lean premixed gas turbine combustors and shortening the lifetime of the overall system. In this study, to understand the instability phenomena, an experimental study and a numerical simulation were conducted in a dump combustor with respect to the modulation of the fuel flow, that is, the choked fuel flow and the unchoked fuel flow. The fluctuations of pressure and heat release were measured by a piezoelectric pressure sensor and high-speed intensified chargecoupled device (ICCD) camera, respectively. Various combustion modes occurred in accordance with the equivalence ratio and the fuel supply conditions. In the low-frequency instability mode, alternative flame behaviors were observed and result from the large equivalence ratio modulation. It is found that, especially in an unchoked fuel flow condition, the modulation of the fuel flow rate affects the characteristics of flame behavior and pressure fluctuations in a lean premixed flame.

Intermittency as a Transition State in Combustor Dynamics: An Explanation for Flame Dynamics Near Lean Blowout

“…However, the intermittency that we refer to involves bursts of high-amplitude periodic oscillations from a background of low-amplitude chaotic or aperiodic fluctuations. This type of intermittency is comparable to the observations of sporadic 'noisy' and 'quiet' states reported in Hong et al (2008) and Arndt et al (2010).…”

“…Hong et al (2008) studied the effect of pressure fluctuations on fuel flow modulations in a swirl combustor. They reported the presence of pressure oscillations with an alternate 'noisy period of 200 Hz fluctuation and a silent period with a small pressure fluctuation' for an unchoked fuel flow at the injector (Fig.…”

Intermittency route to thermoacoustic instability in turbulent combustors

“…For an unchoked fuel flow at the injector in a swirl combustor, Hong et al (2008) reported the presence of pressure oscillations that alternated between a 'noisy period of 200 Hz fluctuation and a silent period with a small pressure fluctuation'. Arndt et al (2010) have observed a transition in the flame dynamics between a state of stable combustion and self-excited oscillations in a premixed gas turbine model 472 V. Nair, G. Thampi and R. I. Sujith combustor using simultaneous OH * chemiluminescence, OH * planar laser-induced fluorescence (PLIF) and stereoscopic measurements.…”

Common features in the thermoacoustics of flames and engines

“…Quasi-periodic and chaotic oscillation: Quasi-periodic pulses about every 0.1 s have been observed by Hong et al 135 in a dump combustor and shown to be associated with equivalence ratio fluctuations and the lifting of the premixed flame in a regime of mean equivalence ratio approaching that of lean blow-out. Also in that regime, Nair et al, 136 Domen et al 137 and Unni and Sujith 138 examine intermittency in pressure fluctuations on a similar timescale in a swirled combustor and proposed it as a diagnostic for blow-out.…”