Study On Fuel Control Logic In FADEC System Of Aviation Auxiliary Power Unit

Auxiliary Power Unit(APU for short)is a small gas turbine engine.It has characteristics such as small volume?light weight?long longevity?short start time by itself?the ability of supply shaft power and constringent air at the same time and the capability of operating alone.Now APU has widely applied in martial and civil airplane,and APU is called for the second power of airplane.APU is developed late interiorly,and FADEC control system will be the mainstream in engine control system for its prominent virtue.The thesis studies the FADEC system applied APU fuel control logic,and solves the speed control problem brought from the characteristics of the APU combustor,which has engineering application value and significance for improving APU development level interiorly.At first the thesis builds the non-linear mathematical model of APU based on components method.Then the thesis studies the APU fuel control logic including the startup control logic?steady-state control logic?the fuel divider control logic and arithmetic implemented actually.The APU simulation test-bed based on APU mathematical model is established to study and validate the APU control logic and control system design.The thesis studies the constitution and principle of the test-bed and detailed design of important system.Simulative tests have done in simulation test-bed and contrasted to the ground test.At last the thesis studies the prevent-flameout strategy to ravel out speed drop phenomenon brought from the characteristics of the APU combustor,analyses the cause of APU speed drop in flight based on the characteristic index of combustor and the fuel control logic.Measure to prevent flameout is provided by adding fuel supply lower limit in the steady-state speed control loop.Test is done in simulation test-bed and the result is contrasted with that without modification to validate the feasibility and validity of the solution.