Model-based analysis and design of active control of thermoacoustic instability

Thermoacoustic instability arises due to the two-way coupling between the heat release dynamics and acoustics in continuous combustion systems, especially those designed to run at lean premixed conditions. While suppression or damping of oscillation is possible under some circumstances, active control promises to provide more flexibility in terms of design, operating conditions and robustness. Optimum designs of the latter must rely on accurate modeling of the underlying mechanisms governing combustion dynamics and a good understanding of the tight and often subtle coupling between actuators, combustion dynamics, acoustics, control algorithms and observers. In this paper, we use an input-output reduced order model of a controlled combustor to illustrate one aspect of such coupling, namely the dependence of the zero dynamics on the relative location of the heat release zone, the actuator and the sensor. We also use the model to design the controller using a linear quadratic Gaussian (LQG) approach. We show that the model response is similar to that obtained using the governing partial differential equations simulations of the process. We also verify the performance of the same controller experimentally using a 1 KW benchtop combustor rig.