POWERPLANT MIDTERM MOD 5

Internal Air System

Internal Air System

defined as those airflows which do not directly contribute to the engine thrust.

combustor and turbine

The principal areas which require air cooling

Cooling Air

used to control the temperature of the compressor shafts and discs by either cooling or heating them.

Pre-Swirl Nozzles

reduce the temperature and pressure of the cooling air fed to the disc for blade cooling.

Seals

used to prevent oil leakage from the engine bearing chambers, to control cooling airflows and to prevent ingress of the mainstream gas into the turbine disc cavities.

Ring Seals

Comprises a metal ring which is housed in a close fitting groove in the static housing.

Hydraulic Seals

This method of sealing is often used between two rotating members to sea a bearing chamber.

Carbon Seals

consist of a static ring of carbon which constantly rubs against a collar on a rotating shaft.

Brush Seals

comprise a static ring of fine wire bristles. They are in continuous contact with a rotating shaft, rubbing against a hard ceramic coating. It has the advantage of withstanding radial rubs without increasing leakage.

Labyrinth Seals

Critical component applied across rotating equipment to seal high pressure areas from low pressure areas and prevent contamination of the process.

Electric

Cartridge

Iso-prophyl-nitrate

Air

Gas Turbine Engine

Hydraulic

Methods of Starting

Electric

Usually a direct current (D.C.) electric motor coupled to the engine through a reduction gear and ratchet mechanism, or clutch, which automatically disengages after the engine has reached a self-sustaining speed.

Cartridge

sometimes used on military engines and provides a quick independent method of starting.

Iso-prophyl-nitrate

This type of starter provides a high power output and gives rapid starting characteristics. It has a turbine that transmits power through a reduction gear to the engine.

Air

used on most commercial and some military jet engines. It has many advantages over other starting systems, and is comparatively light, simple and economical to operate.

Gas Turbine Engine

s 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.

Hydraulic

used for starting some small jet engines. In most applications, one of the engine- mounted hydraulic pumps is utilized and is known as a pump/starter, although other applications may use a separate hydraulic motor.

High Voltage Exciter

High Voltage Transmission Lead

Igniter Plug

The three major components of ignition system.

Intermittent Duty

are of sufficiently high current draw to cause overheat damage to their units, so they have a restricted duty cycle based on operating time, followed by a cooling off period.

Extended Duty

have long duty cycles, or in some cases are rated for continuous duty, meaning they have no time limits all.

High-energy ignition

used for starting all jet engines and a dual system is always fitted.

'joules' (one watts equals one joules per second).

Ignition units are rated in __________.

Transistorized Ignition Unit

similar to that of the D.C. trembler-operated unit, except that the trembler-unit is replaced by a transistor chopper circuit.

D.C. Trembler-Operated Ignition Unit

charges the reservoir capacitor (condenser) through a high voltage rectifier. When the voltage in the capacitor is equal to the breakdown value of a sealed discharge gap, the energy is discharged across the face of the igniter plug.

Constricted or Constrained Air Gap Type

Shunted Surface Discharge Type

two basic types of igniter plug

Air Gap Type

similar in operation to the conventional reciprocating engine spark plug, but has a larger air gap between the electrode and body for the spark to cross.

Surface Discharge Igniter Plug

has the end of the insulator formed by a semi-conducting pellet which permits an electrical leakage from the central high tension electrode to the body.