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Typical fuel metering systems for small gas turbine engines consist of a metering valve and a bypass valve which is maintaining a constant differential pressure across the metering valve orifice. The metering valve is operated by the compressor pressure signal and the bypass valve acts automatically. It is proposed to bring both the metering and the bypass valves under the control of two digital linear actuators. The first one would move the metering plunger according to the compressor pressure and the second would move the bypass plunger in such a way, that the differential pressure across the metering orifice would be maintained constant only during steady state engine operation. During the engine transient processes, however, it would be increased or decreased as required, to speed up the change in the nozzle flow rate and consequently the engine dynamic response.

Contemporary high speed diesel engines require a compromise regarding the size of fuel nozzle orifices which should be small enough to assure a good fuel atomization at low engine speed, and large enough to provide the engine with high fuel dose at maximum power. Calculations were made to predict the dynamic response of a closed diesel injector within its unstable operation range. The pressure in the seat chamber under the needle was established as the key factor to simulate the injector's behaviour. It was measured at different flow conditions and used in calculations. After applying an optimization method, it was possible to predict how the design parameters of an injector should be changed in order to obtain the best dimentional configuration which improves the fuel atomization at low engine speed.