Toward Active Control of Turbulent Combustion — Development of the Demonstration Combustor System — S. Tachibana, L. Zimmer, T. Yamamoto, Y. Kurosawa, S. Yoshida and K. Suzuki Japan Aerospace Exploration Agency 7-44-1 Jindaiji-Higashi, Chofu, Tokyo 182-8522, Japan E-mail: tachibana.shigeru@jaxa.jp March 2, 2004 Abstract The purpose of this work is to develop effective active control means for wide-range stable premixed combustors. We are developing a demonstration combustor system which consists of a target combustor, sensors, actuators and controllers by accumulating the knowledge from the results of fundamental studies among the combustion groups of this project. A methane-air premixed swirl-stabilized combustor was applied as the target combustor. The main premixed flame is stabilized by the axial swirler with orifices for secondary fuel injection on the central hub. For the first step, we set two operating conditions, as typical conditions for a lower and a higher outputs, and investigated natural acoustic modes of combustion oscillation. Several control methods were examined on the unstable points of the conditions. A pressure transducer and a chemiluminescence detector were used as sensors and secondary fuel injections in pulsating/non- pulsating modes were applied as an actuator. Since controller is not built in yet, the parameters needed for actuation were manually set at this point. For the lower output condition, the effects of control methods on the reduction of pressure oscillations is discussed. For the higher output condition, the effects of the amount of secondary fuel injection both on the reduction of pressure oscillation and NOx emission are discussed. 1 Introduction Lean premixed combustion has been considered as a promising way to reduce NOx emission and continuous efforts to build it in the real gas turbine system has been exerted. However, the realization has not been completed yet for some reasons. One main drawback that prevents the realization is the instability of premixed flames. To overcome the difficulties, passive controls have been adopted to the development. In recent days, from the point of view of adaptive flexibility of the control, active control strategies have begun to attract attention and has been examined in many works[1]-[6]. The source of the instability is due to the mutual interaction between fluctuations of pressure and heat- release rate. Hence, for sensors and actuators, there are two standpoints corresponding to each of the components of the instability. Usually, pressure transducers and chemiluminescence detectors are used for sensing pressure and heat-release rate respectively. In a similar way, loud speakers and secondary fuel injections are used for the actuation. From the point of view of application to the real- scale combustor, the actuating energy generated by loud speakers may be too low. Consequently, the secondary fuel injection is considered to be the realistic way for the actuation. In the framework of this project, fundamental studies toward the active control system have con- tinuously been pursued among the combustion groups. Several applications of chemiluminescence information as sensors have been examined by JAXA group[7]. The effects of high-speed secondary fuel injection have been investigated by TIT group[9]. Anti-phase closed loop controls using micro- phone as a sensor and a loud speaker or periodic secondary fuel injection as actuators have been developed by AGU and NMRI groups[10]. CFD studies over the whole combustion chamber have been done by JAXA CFD group[11]. Our goal in this work is to develop a demonstration combustor