The paper aim is to study the transient performance using fuel flow schedule, variable geometry compressor control and combustion emissions for a simple turbojet engine in a thrust class of 5kN. This engine is under development, it was designed, manufactured and are being tested in test bench, it is composed by a 5-stage axial flow compressor, an annular combustor, an uncooled turbine and a convergent nozzle. The engine was originally designed to run on kerosene but other types of fuels, as biofuels, are intended to be used, having in mind a turboshaft in a class of 1.2 MW for power generation purpose. PID control is being studied to determine the appropriate setting of the VIGV in conjunction with a prescribed fuel flow injection necessary to accelerate, or decelerate, the engine from 80% to full thrust in a prescribed time interval. The engine control system is being studied during this engine design phase, so that all the components characteristics needed are being synthesized using in-house developed computer codes: compressor design and performance; combustion chamber design and performance; turbine design and performance; whole engine performance. The engine is required to accelerate from 80% to full thrust in a short time interval, which is also a limitation imposed to the control system. Compressor surge margin is controlled during accelerations using controlled positioning of the VIGV at each engine speed. The engine running lines, for accelerations and decelerations are shown and commented. They served as basis for the design of the engine control logic and hardware. The combustor was designed for kerosene, but other types of fuels can be burned, with the lower heating value and all the necessary parameters recalculated using reaction mechanisms, reactor network and stability loops approach.

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