known for converting fuel energy into propul-  sive energy.  However, the intermittent action  of the reciprocating engine places practical  limits to the airflow that can be processed  and  restricts the development of power.  The con-  tinuous, steady flow feature of the gas turbine  allows such a powerplant to process consider-  ably greater airflow and, thus, utilize a greater  expenditure of fuel energy. While the pro-  pulsive efficiency of the turbojet engine is con-  siderably below that of the reciprocating en-  gine-propeller combination, the specific power  output of the turbojet at high speeds is quite  superior.  The operation of the turbojet engine involves  a relatively large change in velocity being im-  parted to the mass flow through the engine.  Figure 2.6 illustrates the operation of a typical  turbojet engine by considering the processing  given a unit weight of inlet airflow.  Consider  a unit weight of ambient air approaching the  inlet to the engine then experiencing the  changes in pressure and volume as it is proc-  essed by ’ the turbojet.  The chart of pressure  versus  volume of figure 2.6 shows that the unit  weight of airflow at atmospheric condition A  is delivered to the inlet entrance at condition  B.  The purpose of the inlet or diffuser as to  reduce the velocity and increase the pressure  of the flow entering the compressor section.  Thus, the aerodynamic compression produces  an increase in pressure  and decrease  in volume  of the unit weight of air and delivers air to  the compressor  at condition C.  The work done  by the aerodynamic compression of the inlet  ot diffuser is represented by the area ABCX.  Generally, most conventional turbojet engines  require that the compressor inlet flow be sub-  sonic and supersonic flight will involve con-  siderable aerodynamic compression  in the inlet.  Air delivered to the compressor  inlet at con-  dition C is then subject to further compression  through the compressor section. As a result  of the function of the compressor, the unit  weight of air is subject to a decrease  in volume  and increase in pressure to condition D.  The  compressor pressure ratio should be high to  produce a high thermal efliciency in the engine  The area XCDZ represents the work done by  the compressor  during the compression of the  unit weight of air.  Of course, certain losses  and inefliciencies are incurred during the com-  pression and the power required to operate the  compressor  will be greater than that indicated  by the work done on the engine airflow.  Compressed  air is discharged from the com-  pressor  to the combustion chamber at condition  D.  Fuel is added in the combustion chamber,  and the combustion of fuel liberates consider-  able heat energy.  The combustion process in  the gas turbine differs from that of the recipro-  cating engine in that the process is essentially  a constant pressure addition of heat energy.  As a result, the combustion of fuel causes a  large change in temperature and large change  of volume of the unit weight of airflow.  The  process in the combustion chamber is repre-  sented by the change from point D to point E of  the pressure-volume  diagram of figure 2.6.  The combustion products are delivered to the  turbine section where sufficient work must be  extracted to power the compressor section.  The combustion chamber discharges high tem-  perature, high pressure  gas to the turbine where  a partial expansion is accomplished with a drop  in pressure  and increase in volume to point F  on the pressure-volume diagram.  The work  extracted from the unit weight of air by the  turbine section is represented by the area  ZEFY.  As with the compressor, the actual  shaft work extracted by the turbine will differ  from that indicated by the pressure-volume  diagram because of certain losses incurred  through the turbine section.  For steady, sta-  bilized operation of the turbojet engine the  power extracted by the turbine will equal the  power required to operate the compressor.  If  the turbine power exceeds the compressor  power required, the engine will accelerate; if  the turbine power is less than the compressor  power required, the engine will  decelerate.  107  NAVWEPS 00-801-80  ARPLANE PERFORMANCE 