Chapter 23. -GAS TURBINE 



nozzles at the pressure and volume required to 

 maintain the desired engine performance. At the 

 same time, the fuel control governor limits fuel 

 flow to maintain operating conditions within safe 

 limits. 



The fuel nozzles serve to introduce the fuel 

 into the combustion chamber. The fuel is sprayed 

 into the combustion chamber under pressure, 

 through small orifices in the nozzles. Various 

 kinds of fuel nozzles are in use. Figure 23-16 

 shows a simplex nozzle and a duplex nozzle. 

 The simplex nozzle was used on some older 

 gas turbine engines. Most recent gas turbine 

 engines use some kind of duplex nozzle. A duplex 

 nozzle requires a dual manifold just ahead of 

 the nozzles and a flow divider (before the mani- 

 fold) to divide the fuel into primary and sec- 

 ondary streams. The duplex type of nozzle pro- 

 vides a desirable spray pattern for combustion 



SECONDARY 



B 



over twice the range of that provided by the 

 simplex nozzle. 



The fuel control assembly is the unit which 

 regulates the turbine rpm by adjusting fuel flow 

 from the high pressure engine-driven pump to 

 the fuel nozzle. The major parts of the fuel 

 control assembly are shown in figure 23-17. 

 Fuel enters the fuel control assembly and is 

 pumped through a filter. High pressure fuel is 

 routed to the differential relief valve, then to 

 the fuel shutoff valve, and finally to the fuel 

 nozzles. 



The speed setting lever on the outboard end 

 of the governor is connected to a speed control 

 device on the control console either by a cable 

 or by an electric servomotor. At the fuel con- 

 trol end, the lever is keyed to a pinion. This 

 pinion positions a rack which in turn controls 

 the governor flyweight spring. The mechanism 

 regulates gas producer speed according to the 

 position of the control lever. With the control 

 lever in any particular position, variations from 

 the preset speed are sensed by the governor 

 flyweights and a compensating movement of the 

 fuel control valve results. An externally adjust- 

 able needle valve provides a constant minimum 

 fuel flow during deceleration, when the governor 

 valve is closed, to prevent loss of combustion. 

 An acceleration limiter, consisting of a needle 

 valve positioned by a shaft, arm, and bellows, 

 is actuated by compressor discharge pressure. 

 During acceleration, this mechanism controls 

 fuel flow to the point at which the governor fly- 

 weight mechanism and its fuel control valve 

 take over. 



LUBRICATING SYSTEM.-Because of the 

 high operating rpm and the high operating tem- 

 peratures encountered in gas turbine engines, 

 proper lubrication is of vital importance. The 

 lubricating system is designed to supply bear- 

 ings and gears with clean lubricating oil at the 

 desired pressures and temperatures. In some 

 installations, the lubricating system also fur- 

 nishes oil to various hydraulic systems. Heat 

 absorbed by the lubricating oil is transferred 

 to the cooling medium in a lube oil cooler. 



The lubricating system shown in figure 23- 

 18 has a combined hydraulic system— in this 

 case, the hydraulic system is for the operation 

 of a hydraulic clutch in a gas turbine propulsion 



147.150 



Figure 23-16.— Fuel nozzles. 

 A. Simplex. B. Duplex. 



Servomechanisms are discussed in chapter 20 of this 

 text. 



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