Active Combustion Control System Rig Testing

Abstract

A team of Goodrich engineers tested an Active Combustion Control System (ACCS) which was designed to reduce thermo-acoustic instabilities in aircraft gas turbine engines. This testing was conducted on the University of Cincinnati Aerospace Department’s high pressure combustion rig. All testing was conducted utilizing a dual circuit lean burn fuel injector with a high frequency modulating valve on the pilot circuit. The purpose of this testing was to determine how to best implement this system to control a thermo-acoustic combustion instability. Open loop control methods utilized during these experiments included off-frequency single tone forced modulation, broad-band random frequency generation, and narrow-band random frequency generation. Closed loop control methods included frequency tracking only, frequency and phase tracking, and frequency, phase, and amplitude tracking. The results of the testing utilizing frequency, phase, and amplitude tracking was a reduction in combustion instability of 22% RMS and a 58% reduction based on the FFT peak response of the dominant frequency tone. The purpose of this paper is to present the results of these tests. I. Introduction OODRICH has been working on an Active Combustion Control System (ACCS) for aircraft gas turbine engines since 2003. The system includes the following Goodrich proprietary components: high frequency (1000 hertz) modulating valve, acoustic dynamic pressure sensor, and optical flame sensor, and control system designed to mitigate thermo-acoustic combustion instabilities. Testing discussed in this paper also includes the use of Goodrich Triple Annular Research Swirler (TARS) fuel injector designed specifically to simulate real world lean combustion systems based on a 1983 AIAA paper by Sanborn, Mongia, and Kidwell. The aforementioned hardware was installed and tested as a complete system in the University of Cincinnati high pressure combustion rig. Testing involved setting the fuel-to-air ratio of the main combustion flame at a point which was inherently unstable and then modulating the pilot fuel pressure so that the heat release of the pilot flame is out of phase with the measured combustion instability in order to actively reduce the magnitude of the instability. Instability measurements were provided by fuel injector mounted optical flame sensors and acoustic dynamic pressure sensors. During the testing active control provided reductions in combustion instability of up to 22% RMS and 58% FFT peak response compared to uncontrolled cases. Results were consistent over the duration of the tests and repeatable. The key combustion control components for the Goodrich ACCS include: