Heat release dynamics modeling for combustion instability analysis of kinetically controlled burning

Abstract

We present a heat release dynamics model which utilizes a well-stirred reactor (WSR) model and one-step kinetics to describe the unsteady combustion process. The model incorporates the linearized mass and energy equations to describe the response of the reactor to external perturbations, and is cast in the form of a first order filter. The model is able to predict the phase between the mass flow rate oscillations and the resulting heat release fluctuations, as function of the operating conditions, e.g., the mean equivalence ratio and mean mass flow rate. The model predicts a sudden shift in phase in the region between the maximum reaction rate and the blow-out limit. We show that this phase change may trigger combustion instability. We use this novel model to predict combustion instability conditions in high swirl combustion, and demonstrate that these predictions agree qualitatively with experimental studies.2

Reduced order modeling of reacting shear flow

“…(4) can be determined using Ĝ , which is the solution of (5), and the integrals in (6) and (7). Ĝ in turn, can be computed as…”

“…(6) and (7). The inverse transform in (7), from the frequency to the time domain, is performed by adding the residues of singularities in the integrand Ĝ . This is obtained as …”

“…Characterized by a positive Rayleigh Index, obtained when the pressure and heat release perturbations are in phase, the instability occurs normally at frequencies that are associated with acoustic modes that can be identified as a longitudinal, azimuthal, or bulk mode depending on the configuration of the combustor. These interactions have been modeled in a number of recent investigations by including acoustics and heat-release dynamics as primary components [1][2][3][4][5][6][7].…”