Active control of oxy-fuel combustion using preflame CO2-injection

Thermoacoustic instabilities in combustion processes have received considerable of attention in recent years. Coupling between heat release from the flame and acoustic, causes large high frequency pressure oscillations that are unwanted. The most promising way to stabilize such a system, is to perturb the system by injecting small amounts of gas close to the flame. To allow the injected gas to mix well with the main flow before burning, the injector must be placed upstream of the flame. This introduces an unwanted time delay due to transport of injected gas to the flame, and because of the high frequency of the unstable oscillations, even small time delays can be a problem. In this paper we focus on control of a low order oxy-fuel combustion model with a time delay. We apply a procedure that can calculate the intervals of time-delays for which the system can be stabilized. This is useful during design of the combustion chamber, as it allows us to place the injector at an optimal location. For the low order model, it also gives us exact knowledge about how much operating conditions of the combustion chamber can change, before the controller becomes unable to stabilize the system. Further it allows us to find controller tunings that can handle a wide range of time-delays, and are robust toward modeling errors.