THE PULSEJET ENGINE
heated externally by burning oil sprays.) The
amount of heat you can add is largely dependent
The "intermittent impulse" jet engine (fig. 1-8),
upon the pressure of the air treated. A simple
known as the aeropulse or pulsejet improves
method of raising the pressure is to pass the air
compression by sacrificing the principle of con-
through a DIVERGENT entry nozzle. A divergent
tinuous power generation. The pulsejet is like the
entry nozzle decreases the velocity of the air and
ramjet, but with a series of nonreturn shutter
increases the pressure. This also provides a for-
valves. Fuel injection nozzles located just aft of
ward pressure wall for the jet to react. A
the shutter valves provide fuel. As the engine
CONVERGENT exit nozzle further increases the
travels through the air, pressure on the nose opens
jet velocity. The simple gas unit (fig, 1-6) created
the valve and rams air into the duct, mixing air
has little practical use because of the following:
with fuel. Igniting the combustible mixture creates
1. Air compression depends solely on "ram
a high pressure (from the expanding gases), clos-
effect."
ing the valves. The violent ejection of the gases
2, A limited amount of heat is added.
forms a relatively low-pressure area inside the
3. Considerable heat is lost by radiation.
duct, admitting a fresh charge of air through the
The next step is to improve the method of
flat spring valves. Because of the temperature of
the duct and the return of part of the flaming
adding heat, through internal combustion.
exhaust gases, the rest of the charges burn without
Figure 1-7 shows a divergent-convergent duct.
an igniter plug. This operating cycle or pulsations
Fuel is injected and burned, releasing heat directly
into the airstream. This simple "Aero THermO
creates a loud buzzing sound. "Buzz bomb"
DYnamic Duct" (ATHODYD) or RAM JET is
described an early application of this unit, the
German V-1 flying bomb.
used in remotely piloted vehicle (RPV) and cruise
We learned the basic principle of jet propul-
missiles.
sion with the rocket. The ram jet taught us that
adding heat would expand the gases and increase
velocity. It also showed the amount of heat that
is possible to add is dependent upon the amount
Figure 1-8.-The aeropulse or pulsejet.
Figure 1-6.-A convergent discharge nozzle.
Figure 1-7.-The ramjet engine.
1-3
