Page 134 - The Jet Engine

Starting and ignition

Fig. 11-4 A triple-breech cartridge starter.

Cartridge air pump scavenges the starter combustion chamber
7. Cartridge starting is sometimes used on military of fumes before each start. Operation of the fuel and
engines and provides a quick independent method of air pumps, ignition systems, and cycle cancellation,
starting. The starter motor is basically a small is electrically controlled by relays and time switches.
impulse-type turbine that is driven by high velocity An iso-propyl-nitrate starting system is shown in fig.
gases from a burning cartridge. The power output of 11-5.
the turbine is passed through a reduction gear and
an automatic disconnect mechanism to rotate the Air
engine. An electrically fired detonator initiates the 9. Air starting is used on most commercial and
burning of the cartridge charge. As a cordite charge some military jet engines. It has many advantages
provides the power supply for this type of starter, the over other starting systems, and is comparatively
size of the charge required may well limit the use of light, simple and economical to operate.
the cartridge starters. A triple-breech starter is 10. An air starter motor transmits power through a
illustrated in fig. 11-4. reduction gear and clutch to the starter output shaft
which is connected to the engine. A typical air starter
Iso-propyl-nitrate motor is shown in fig. 11-6.
8. This type of starter provides a high power output
and gives rapid starting characteristics. It has a 11. The starter turbine is rotated by air taken from
turbine that transmits power through a reduction gear an external ground supply, an auxiliary power unit
to the engine. In this instance, the turbine is rotated (A.P.U.) or as a cross-feed from a running engine.
by high pressure gases resulting from the The air supply to the starter is controlled by an elec-
combustion of iso-propyl-nitrate. This fuel is sprayed trically operated control and pressure reducing valve
into a combustion chamber, which forms part of the that is opened when an engine start is selected and
starter, where it is electrically ignited by a high- is automatically closed at a predetermined starter
energy ignition system. A pump supplies the fuel to speed. The clutch also automatically disengages as
the combustion chamber from a storage tank and an the engine accelerates up to idling r.p.m. and the

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