A further Note no Active Cpmtrol of Combustion instabilities Besed on Hyeteresis

When do open-loop strategies for combustion control work?

“…For stabilization using hysteresis, we need a pulse of sufficient duration and height so that the equivalence ratio ¦ C can become effective following which the system can return to the desired operating point B in Figure 2 , stabilization will occur. This confirms the observations (O1)-(O3) in [5]. As with the infinite switching strategy, we note that the robustness of this single pulse strategy is non-existent; as long as perturbations are present, the operating point will move from è to ¥ causing pulsing to be invoked repeatedly.…”

“…This is similar to the stable-unstable switching we considered. A third statement we can make is It is quite likely that the primary loop of the hysteresis curve in [5,4] corresponded to an equivalence ratio change that is commensurate with a 25% change in the fuel-flow rate. This discussion shows that (39) provides sufficient conditions for stabilization with infinite switching in the presence of hysteresis.…”

“…Such a strategy has been employed in a number of recent investigations including [1]- [5]. Using a physically based model, analytical explanations for the effectiveness of such a low pulsing strategy are provided in this paper.…”

“…(ii) model-based control, which consists of developing a physically based model of the combustion dynamics and have been demonstrated to yield an optimal stabilizing response under certain conditions, [14]- [17], (iii) observer-based control [18], which have been shown to result in satisfactory pressure suppression using an on-line determination of an observer and a phase-shift controller based on the observer parameters, (iv) control based on system-identification based modeling [19,20] and (v) open-loop control strategies [1,2], [21]- [5] where the mass-flow rate of a fuel injector (and therefore the equivalence ratio) is switched between two different values at a significantly slower frequency than the resonant frequency. This paper concerns analytical discussions of the last method listed above.…”

When Do Open-Loop Strategies for Combustion Control Work?

“…In [3], a similar low-frequency modulation was used. In [4,5], the presence of hysteresis in the combustor was used to design a low-frequency pulsing strategy to suppress the pressure oscillations. In [1], a 20 kW gas turbine combustor was stabilized, with a resonant frequency of 300 Hz and an equivalence ratio of 0.85, using a fuel-injector oscillated at 50 Hz and at duty cycles between 0.36 and 0.5.…”