CHAPTER 23 



GAS TURBINES 



The gas turbine engine, long regarded as 

 a promising but experimental prime mover, 

 has in recent years been developed to the point 

 where it is entirely practicable for ship pro- 

 pulsion and for a number of auxiliary applica- 

 tions. Gas turbine engines are currently in- 

 stalled as prime movers on minesweepers, 

 landing craft, PT boats, air-sea rescue boats, 

 hydrofoils, hydroskimmers, and other craft. In 

 addition, the gas turbine engine is finding in- 

 creasing application as the driving unit for 

 ship's service generators, pumps, and other 

 auxiliary units. 



Although the gas turbine engine as a type 

 need no longer be regarded as experimental, 

 many specific models of gas turbine engines are 

 still at least partially experimental and subject 

 to further change and development. The discus- 

 sion in this chapter therefore deals primarily 

 with the general principles of gas turbine 

 engines rather than with specific models. De- 

 tailed information on any specific model maybe 

 obtained from the manufacturer's technical man- 

 ual furnished with the equipment. 



BASIC PRINCIPLES 



The gas turbine engine bears some resem- 

 blance to an internal combustion engine of the 

 reciprocating type and some resemblance to a 

 steam turbine. However, a brief consideration 

 of the basic principles of a gas turbine engine 

 reveals several ways in which the gas turbine 

 engine is quite unlike either the reciprocating 

 internal combustion engine or the steam turbine. 



Let us look first at the thermodynamic 

 cycles of the three engine types. The recipro- 



cating internal combustion engine has an open, 

 heated-engine cycle and the steam turbine*^ has 

 a closed, unheated- engine cycle. In contrast, the 

 gas turbine has an open, unheated- engine cycle— 

 a combination we have not previously encoun- 

 tered in our study of naval machinery. The gas 

 turbine cycle is open because it includes the 

 atmosphere; it is an unheated-engine cycle be- 

 cause the working substance is heated in a de- 

 vice which is separate from the engine. 



Another way in which the three types of 

 engines differ is in the working substance. The 

 working fluid in a steam turbine installation is 

 steam. In both the reciprocating internal com- 

 bustion engine and the gas turbine engine, the 

 working fluid may be considered as being the 

 hot gases of combustion that result from the 

 burning of fuel in air. However, there are very 

 important differences in the way the working 

 fluid is used in the reciprocating internal com- 

 bustion engine and in the gas turbine engine. 



Still other differences in the three types of 

 engines become apparent when we consider the 

 arrangement and relationship of component parts 

 and the processes that occur during the cycle. 

 From our study of previous chapters of this 

 text, we are already familiar with the functional 

 arrangement of parts in steam turbine installa- 

 tions and in reciprocating internal combustion 

 engines. Now let us look at the relationship of 

 the major components in a basic gas turbine 

 engine, as illustrated schematically in figure 

 23-1. 



In the steam turbine installation, the proc- 

 esses of combustion and steam generation take 



Thermodynamic cycles are discussed in chapter 8 of 

 this text. 



Internal combustion engines are discussed In chapter 



22. 

 3 

 Steam turbines are discussed In chapter 12 and In 



chapter 16. 



595 



