Starting and ignition - Gas turbine

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Gas turbine
14. A gas turbine starter is used for some jet engines and is completely self-contained. It has its own fuel and ignition system, starting system (usually electric or hydraulic) and self-contained oil system. This type of starter is economical to operate and provides a high power output for a comparatively low weight.

Fig. 11-9 A gas turbine starter.

15. The starter consists of a small, compact gas turbine engine, usually featuring a turbine-driven centrifugal compressor, a reverse flow combustion system and a mechanically independent |free-power turbine. The free-power turbine is connected to the main engine via a two-stage epicyclic reduction gear, automatic clutch and output shaft.  A typical gas turbine starter is shown in fig. 11-9.





16. On initiation of the starting cycle, the gas turbine
starter is rotated by its own starter motor until it reaches self-sustaining speed, when the starting and ignition  systems  are  automatically  switched  off. Acceleration then continues up to a controlled speed of approximately 60,000 r.p.m. At the same time as the gas turbine starter engine is accelerating, the exhaust gas is being directed, via nozzle guide vanes, onto the free-power turbine to provide the drive to the main engine. Once the main engine reaches  self-sustaining  speed,  a  cut-out  switch operates and shuts down the gas turbine starter. As the  starter  runs  down,  the  clutch  automatically disengages from the output shaft and the main engine accelerates up to idling r.p.m. under its own power.