When do open-loop strategies for combustion control work?

Abstract

This paper addresses open-loop control strategies that involve a low frequency modulation of the fuel injection for suppression of pressure oscillations in combustion systems. 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. Conditions are derived on the frequency and the duty-cycle used in the control strategy that lead to stabilization in the combustor, under ideal and nonideal switching strategies, and in the presence of hysteresis.

Review of advances in combustion control, actuation, sensing, modeling and related technologies for air breathing gas turbines

“…Many authors (Jones, Lee, andSantavicca (1999), Prasanth, Annaswamy, Hathout, andGhoniem (2000), Richards, et al (1999), andBrouwer, Ault, Bobrow, andSamuelsen (1990)) have been working on sub-harmonic, and low frequency (sometimes referred to as low bandwidth) fuel modulation or control. Typically linear models are used when employing this type of control.…”

“…Typically linear models are used when employing this type of control. Low frequency type of actuation is believed too be effective because it "hops over" the instability (Prasanth, Annaswamy, Hathout, and Ghoniem (2000)). Trade studies are continuing to determine if this type of control is more cost effective than traditional modulation at the frequency of interest.…”