gsphelp  Turboshaft Fuel control

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gsphelp  Turboshaft Fuel control

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SC_TurboShaftFCIcon

 

The turboshaft fuel control component offers a generic fuel control system model for free power turbine turboshaft engines. It is derived (inherited) from the Gas generator fuel control component and includes all functionality to control the gas generator. In addition, the turboshaft fuel control has a PID controller (PT governor) for the power turbine shaft speed, which outputs a signal to the gas generator controlling either one of the following parameters depending on the PT Governor output option in the PT Control tab sheet:

Power Lever Angle PLA

Demanded gasgenerator shaft speed N

Fuel massflow over combustor pressure Wf/pb

Fuel massflow Wf

 

The gas generator control logic is fully inherited from the Gas generator fuel control component (including maximum acceleration / minimum deceleration schedules etc.). Functionality from the gas generator control component is used, with the starting point depending on the on the PT governor output option. In case the PT Governor outputs a Wf signal (option 4) for example, all Gas generator functions are skipped except for the fuel pump first order lag transfer function.

As with the Gas generator fuel control component, many simple turboshaft rotor speed governors can be modelled accurately. For more complex (e.g. FADEC, Full Authority Digital Engine Control) control systems characteristics, the component is useful when detailed control aspects can be neglected, such as in gas turbine transient performance trade-off studies. For detailed models of complex control systems, usually custom components are required.

 

Similar to the integrated Gas generator control, there is an additional 'Fully trimmed steady state' option (in the "PT control" tab sheet) for PT governor to calculate fully trimmed steady state operation with the power turbine power balance fully matched at user specified rotor speed. For the Power turbine, this option works different from the gas generator case: only a state is added for the the trimmer output. No error variable is added and an error variable has to be provided by another component. This will normally be from a (power) turbine component, i.e. a turbine component with the Power turbine option set and the 'Power balance at rotor speed' option set to add the error variable. This enables the calculation of fully trimmed free-power turbine turboshaft steady state points (the free power turbine power matching the power load).Normally the load would be varied and the 'Fully trimmed steady state' would provide fully trimmed control states providing sufficient fuel to maintain free power turbine rotor speed at this load.

Please note that this option only works for steady state calculations !

 

Note: steady state and steady state series calculations may become problematic when control system components with engine parameter feedback depending on time (such as Gas Generator Fuel control and Turboshaft Fuel control components) are used in the model. The best way to calculate a steady state point then is to stabilize at the particular operating point using a transient calculation first before performing a steady state calculation.