Surge Line Measurement of a Gas Turbine Engine by Fuel Spiking Test

Abstract

A fuel spiking test was performed to find out a surge line of the compressor in a gas turbine engine. During the test, fuel spiking signal was superposed on the engine controller demand signal and the mixed signal was used in controlling a fuel control valve. For the superposition, a subsystem composed of a fuel controller and a function generator was used. During the fuel spiking test, the original fuel signals and the modified signals were compared to guarantee the consistency excluding the fuel spiking signals. The fuel spiking signal was carefully selected to keep the engine speed constant. The fuel spiking effect was checked by three dynamic pressure sensors. Sensors were placed at the front of the fuel control valve, at the rear of the fuel control valve, and at the compressor discharge location, respectively. Also, three accelerometers were set up on the outer casing of the compressor part to measure the vibration of the engine during the fuel spiking. In the engine test, the effect of the fuel spiking signals modulated by spiking time and amplitude were examined in order to move the operating point up to the surge region without any change of the engine speed. The real engine test was performed at the Altitude Engine Test Facility (AETF) in Korea Aerospace Research Institute (KARI). In the preliminary test, the fuel spiking signals are in good agreement with the dynamic pressure of the fuel flow. The compressor discharge pressure also shows the fuel spiking effects as expected at the compressor. After the preliminary test, fuel spiking signals with 12.5~50ms in time and 84~505% in excessive fuel flow were applied to find out a surge point at specific engine speed. The test result shows that the fuel spiking is a very effective method to make surge. This experimental data could give actual surge line information of a real engine.