JT8D Ignition System
The ignition supplies
a fast sequence of electrical sparks to ignite the fuel / air mixture
in combustion chambers 4 and 7. It is used when the engine is started
(on the ground) or restarted in flight. It is also used as a precaution
to prevent flameout during take off, landing and bad weather. It's controlled
via the flight deck when turned on electrical current flows from the aircraft
supply to the exciter. The exciter sends these high energy sparks via
the high tension leads to the igniters. Each electrical pulse cause the
igniter to produce a strong spark at it's tip in the combustion chamber.
**Note** The electrical output pulse from the exciter has two parts which occur in a very fast sequence. The first part causes the Trigger Spark and the second part cause the Hot Spark.
Seven combustion chambers that do not have igniters have there mixtures ignited by a flame that propagates through the cross over tubes between adjacent cans.
The are two types
of system on the 727.
All of the ignition system components are LRU's