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. 
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. 
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. 
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. 
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 
107 
NAVWEPS 00-801-80 
ARPLANE PERFORMANCE 
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