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The potential benefits of digital electronic controls, including increased flexibility and lower cost, have not yet been fully applied to the small gas turbine engines of remotely piloted vehicles. For these applications, the need for low cost is a strong factor in design. To address this situation, a new, simple and inexpensive electronically controlled metering system for small gas turbine engines is proposed. The system incorporates a diaphragm type valve keeping a constant differential pressure across a stepper motor actuated metering valve. To optimize the design, mathematical models were created for computer simulation. Experimental tests performed on a prototype showed that it can adequately meet the fuel schedules of small gas turbines. The simulation models were validated against the test results and were used in design optimization.

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.

Optimization of diesel injection system using computer aided design involves complex high speed, high pressure hydraulic transient process calculation. To find the fuel discharge characteristic from injector, the fuel pumping process is first computed based on the design parameters of the injection pump. Then, knowing the forward propagating pressure wave, the dynamic response of the injector is calculated resulting in the fuel discharge process. However, if the forward pressure wave could be precisely measured instead of being calculated, and then substituted into the computer program the total calculation procedure would be substantially reduced. In this paper, a computer controlled data acquisition system with high sampling rate was used to record the fuel pumping process in a specially made long pipe to avoid distortion by the reflected pressure wave. This method is convenient, quite accurate and can save the time of computer simulation.