Passive Control of Forced Combustion Instability in a Swirl-Stabilized Spray Combustor

Abstract

A coannular swirl-stabilized burner, equipped with a pulsation mechanism to introduce controlled periodic instability into the fuel flow to the nozzle, was used to examine instability mechanisms and demonstrate passive control of combustion instability. The effects of swirl configuration and airflow distribution on forced, unstable combustion were examined. Fuel pulsation was used to excite a dynamic response from the combustor that would mimic the behavior of instabilities encountered in many commercial, military, and industrial systems. The response of a spray flame to pulsations of different frequencies was examined using a sound spectrum analyzer and particle image velocimetry. The effect of swirl distribution in the burner, including co- and counterswirl distribution, on the amplitude response of three different flames to low-frequency fuel pulsation was examined. An analysis of the flame structure at different points during the cycle of a forced, low-frequency instability is presented for three swirling spray flames. The effect of airflow distribution on the dynamic response of one flame obtained with a particular swirl configuration is presented. Changes in swirl distribution, which affected recirculation and mixing, were found to reduce the magnitude of the flame response to forcing. Changes in airflow distribution, which affected residence times of product gases in the combustion region, were also found to reduce the combustor response to forcing. Changes in swirl and airflow distribution in a burner of this type were shown to provide effective passive control of combustion instabilities.