j. Ignition Systems. Turbine ignition systems are
operated for a brief period during the engine-starting
cycle, and, as a rule, more trouble-free than the typical
reciprocating engine ignition system. Most turbine
engines are equipped with a high-energy, capacitor-type
(1) System components. A typical ignition system
includes two exciter units, two transformers, two
intermediate ignition leads, and two high-tension leads.
Thus, as a safety factor, the Ignition system is actually a
dual system, designed to fire two igniter plugs. Figure
8-13 shows one side of a typical Ignition system.
(2) Igniter plugs. The igniter plug of a turbine
engine ignition system differs considerably from the
spark plug of a reciprocating engine ignition system. Its
electrode must be capable of withstanding a current of
much higher energy than the electrode of a conventional
spark plug. This high-energy current can quickly cause
electrode erosion, but the short periods of operation
minimize this aspect of Igniter maintenance. The
electrode gap of the typical igniter plug Is designed
much larger than that of a spark plug, since the
operating pressures are much lower and the spark can
arc more easily than Is the case for a spark. Finally,
electrode fouling, so common to the spark plug, is
minimized by the heat of the high-intensity spark.
Typical igniter plugs are shown in figure 8-14.
k. Fuel Systems. The fuel system must deliver to the
combustion chambers not only in the right quantity, but
also in the right condition for satisfactory combustion.
The fuel nozzles form part of the fuel system and
atomize or vaporize the fuel so that it will ignite and bum
efficiently. The fuel system must also supply fuel so
that the engine can be easily started on the ground and
In the air. This means that the fuel must be injected into
the combustion chambers in a combustible condition
when the engine is being turned over slowly by the
starting system, and that combustion must be sustained
while the engine Is accelerating to its normal running
Figure 8-11. Speed-Sensitive Control