PRINCIPLES OF NAVAL ENGINEERING 



STARTER 



COMBUSTION 

 CHAMBER 



COMPRESSOR 



SHAFT 



TURBINE 



PROPULSION 



POWER 



COUPLING 



ATMOSPHERIC 

 AIR INTAKE 



EXHAUST TO 

 ATMOSPHERE 



147.135 

 Figure 23-1.— Schematic diagram showing relationship of parts in single-shaft gas turbine engine. 



place in the boiler, while the process by which 

 the thermal energy of the steam is converted into 

 mechanical work takes place in the turbine. In 

 the reciprocating internal combustion engine, 

 three processes— the compression of atmos- 

 pheric air, the combustion of a fuel-air mixture, 

 and the conversion of heat to work— all take 

 place in one unit, the cylinder. The gas turbine 

 engine is similar to the reciprocating internal 

 combustion engine in that the same three proc- 

 esses—compression, combustion, and conver- 

 sion of heat to work— occur; but it is unlike the 

 reciprocating internal combustion engine in that 

 these three processes take place in three sepa- 

 rate units rather than in one unit. In the gas 

 turbine engine, the compression of atmospheric 

 air is accomplished in the compressor; the com- 

 bustion of fuel is accomplished in the combus- 

 tion chamber; and the conversion of heat to work 

 is accomplished in the turbine. 



Many different types and models of gas 

 turbine engines are in use. The gas turbine 

 engine shown in figure 23-1 is called a single - 

 shaft type because one shaft from the turbine 

 rotor drives the compressor and an extension 

 of this same shaft drives the load. 



The gas turbine engine shown in figure 23-2 

 is called a split- shaft type. This engine is con- 

 sidered to be split into two sections: the gas- 



producing section, or gas generator, and the 

 power turbine section. The gas-generator sec- 

 tion, in which a stream of expanding gases is 

 created as a result of continuous combustion, 

 includes the compressor, the combustion cham- 

 ber (or chambers), and the gas-generator tur- 

 bine. The power turbine section consists of a 

 power turbine and the power output shaft. In this 

 type of gas turbine engine, there is no mechani- 

 cal connection between the gas-generator tur- 

 bine and the power turbine. When the engine is 

 operating, the two turbines produce basically the 

 same effect as that produced by a hydraulic 

 torque converter. The split shaft gas turbine 

 engine is well suited for use as a propulsion 

 unit where loads vary, since the gas-generator 

 section can be operated at a steady and con- 

 tinuous speed while the power turbine section 

 is free to vary with the load. Starting effort 

 required for a split-shaft gas turbine engine 

 is far less than that required for a single-shaft 

 gas turbine engine connected to the reduction 

 gear, propulsion shaft, and propeller. 



In the twin- spool gas turbine engine (fig. 

 23-3) the air compressor is split into two 

 sections or stages and each stage is driven 

 by a separate turbine element. The lowpressure 

 turbine element drives the low pressure com- 

 pressor element and the high pressure turbine 

 element drives the high pressure compressor 



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