A Method to Control Turbofan Engine Starting by Varying Compressor Surge Valve Bleed
This thesis reports the results of a study of the starting conditions of a turbofan engine. The research focused on ways to minimize turbine inlet temperature while maintaining an adequate compressor stall margin during engine start by varying the surge valve bleed. Varying the surge valve bleed was also shown to reduce compressor and fan required torque.
A new method of turbofan engine component characteristic map extrapolation was developed. This novel method uses incompressible similarity laws, but compressibility effects of the flow are reflected by changing the exponent used in the similarity laws. These extrapolated component characteristic maps were tested in a simulation of the turbofan engine by stepping engine speed from close to ignition speed to idle speed. The simulation predictions were verified by comparing them to experimental engine performance data.
Lastly, a parametric study of starting surge valve flow area schedule was performed to reduce turbine temperatures while maintaining adequate stall margin. Minimizing turbine inlet temperatures during start-up when turbine components are cold will minimize thermal shock and thereby extend turbine component life.