Aircraft Engine Starting and Ignition Systems Solomon Bezuneh

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PPC-4

AIRCRAFT ENGINE STARTING AND

IGNITION SYSTEMS

Solomon Bezuneh

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Course Features

• Instructional time:- Theory—40 HR

Practical---40HR

References: EA-AC65-12A, Powerplant

: EA-AC65-15A, Airframe

: POWERPLANT, Dale Crane

: A/C POWERPLANT, Bent

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This section covers—20hrs

• 1. Aircraft Engine Starting Systems

a. Reciprocating Engine Starting

b. GTE Starting

• 2.GTE Ignition Systems

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Course Outline

• Engine Starting System

1. Reciprocating Engine Starting Systems

a. Inertia Starters

1. Hand inertia starters

2. Electric inertia starters

3. Combination inertia starters

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Course outline

• b. Direct-cranking electric

1. Small aircraft version

2. Large aircraft version

c. Electric starters for small engines

1. Overrunning clutch

2. Bendix drive

3. Right-angle drive adapter

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Course outline

• 2. Gas Turbine Engine Starters

a. GTE Starting Sequence

b. GTE Electric Starters

1. Direct-cranking electric starters

2. Starter-generators

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Course outline

• c. Air Turbine Starters

1. Cartridge-pneumatic starter

2. Fuel-air combustion starter

3. Gas turbine starter

4. Cartridge starter

5. Air impingement starter

6. Hydraulic starter

7. Hand crank starter

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Aircraft Engine Starters

• DEFINITION: A STARTER IS A MECHANISM CAPABLE OF DEVELOPING LARGE AMOUNTS OF MECHANICAL ENERGY(TORQUE) THAT CAN BE APPLIED TO AN ENGINE CAUSING IT TO ROTATE.

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Evolution of Starting Systems

• Hand-propping

• Hand-starting with bungee cords

• (Gasoline/ether priming)

• Compressed air

• Cartridge starter

• Inertia starter

• Direct cranking starter

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Evolution

• A number of different engine starting devices have been used throughout the development of the aircraft reciprocating engines such as hand-propping, bungee cords, booster magneto, compressed air, cartridge starter, inertia starter & direct cranking.

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Inertia Starters

• Not in common use.

• Operation depends on kinetic energy stored in a rotating flywheel.

• Three types

1. Hand inertia starters

2. Electric inertia starters

3. Combination inertia starters

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Inertia….

Steps in starting;

• Energy storage/Energizing

• Engagement

• Energy transfer/Rotation

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Direct-cranking starters

• Hand direct-cranking

• Electric direct-cranking

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Starters….

Starting

• Pinion engagement to engine

• Energization

• Engagement of pinion to motor

• Engine rotation

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Starters..

After starting

• De-energize motor

• Disengagement of pinion from motor

• Disengagement of pinion from engine

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Small engine starters

• Overrunning clutch

• Bendix Drive

• Right-Angle Drive Adapter

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GAS TURBINE ENGINE STARTING SYSTEMS

• ELECTRICAL

• AIR START

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GTE Starting--General

• Gas turbine engines are generally started by starter power input to the main accessory gearbox which in turn rotates the compressor.

• On the dual-spool-compressor gas turbine engine, the starter rotates the high pressure compressor system only.

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• Compressor rotation by the starter provides the engine with sufficient air for combustion and aids the engine in accelerating to idle speed after combustion occurs.

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• The starter is normally initiated by a cockpit switch, but it is often automatically stopped by a speed sensor device or undercurrent relay at 5-10% RPM after self-accelerating speed is reached.

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• The basic types of starters which have been developed for gas turbine engines are D.C. electric starters and air turbine starters.

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AIR TURBINE STARTERS

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1.Cartridge-pneumatic starter

• Is an accessory gearbox-mounted starter which can use either an explosive charge like cartridge starter or a low pressure, high volume air source similar to the air turbine starter.

• Advantages• Self-contained starts possible for large engines• Very high torque-to-weight ratio• Quick starts possible for military

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Cartridge-pneumatic starter

• Automatic starts possible

• May also be used as an air turbine starter

• Disadvantages

• Cartridge needed for each start

• Gearbox, clutch, and oil system necessary

• No motoring possible for systems checkout

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2. Fuel-air starter

• The fuel/air combustion starter was developed primarily for short-flight, air-carrier aircraft. But it is now replaced by air turbine starter.

• It is an accessory gearbox-mounted starter which utilizes a high pressure air source and a combustion process.

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Fuel-air starter

It is similar to a small gas turbine engine which delivers its power through a high-ratio reduction gear system.

• The starter consists of a turbine-driven power unit and auxiliary fuel, air, and ignition systems.

• The operation in most installations is fully automatic.

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Fuel-air starter

Actuation of a single switch causes the starter to fire and accelerate the engine from

rest to starter cutoff speed.

• Advantages

• Completely self-contained

• High torque-to-weight-ratio

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Fuel-air starter

• Automatic starts possible

• Engine may be motored for short periods on internal air supply at low RPM

• Disadvantages

• Relatively complex

• Only two self-contained starts possible

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3. Air-turbine (pneumatic) starter

• The air turbine starters were developed as high power-to-weight ratio device. They provide high starting torque from a small, light weight source.Parts

• The typical air turbine starter consists of an axial flow turbine which turns a drive coupling through a reduction gear train and a starter clutch mechanism.

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Air-turbine (pneumatic) starter

Operation• The air to operate an air turbine starter is

supplied from either a ground-operated or airborne compressor unit or the bleed air from another engine.

• The air is directed through a combination pressure regulating and shut-off valve in the starter inlet ducting.

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This valve regulates the pressure of the starter operating air and shuts off the air supply when the maximum allowable starter speed has been reached.

• The pressure-regulating and shutoff valve usually consists of two subassemblies:-

• The pressure-regulating valve• The pressure-regulating valve control

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Advantages• High torque to weight ratio (5 to 10 times

higher than electric motor)• Engine may be motored at low or high speed• Can use air from a running engineDisadvantages• High-volume air supply required• Gearbox needed with self-contained oil supply• Electrical connections needed for speed

control

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4. Gas-turbine

• It is a complete miniature gas turbine engine.

• Advantages

• Completely self-contained starts possible

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Gas-turbine

• High torque-to-weight ratio

• Long periods of engine motoring possible

• Disadvantages

• One of the most complex of starter types in that it requires all of the systems of the main engine, plus an overrunning clutch.

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5. Cartridge starter

• It is also called the solid-propellant starter. The starter is used on some large turbine engines.

• It is similar in operation to the air turbine starter; except for burning a solid-propellant charge to supply the energy for starting.

• Advantage• High starting torque-to-weight ratio

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Cartridge starter

• Disadvantages

• Dangerous fuels

• Complex system required

• Cartridge needed for each start

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6. Air impingement

• Air is blown directly on the compressor or turbine of the engine. It is

sometimes called turbine-Impingement starter. It consists of jets of

compressed air piped to the inside of the compressor or turbine case so

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Air impingement

that the jet air-blast is directed onto the compressor or turbine rotor

blades, causing them to rotate.

• A low pressure, high volume air source of 40PSIG at 200 to 300 lb/min

is directed on to the engine turbine wheel. The air source terminates

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Air impingement

after self-accelerating speed is reached.

• 1. Advantages

• Simplest of all types

• Can be used to motor engine, but only with continuous air supply

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Air impingement

• Extremely light

• Can use air from another running main engine

• 2. Disadvantages

• Requires a high-volume air supply (3 to 5 times the pneumatic energy requirements of the air turbine starter).

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7. Hydraulic

• An accessory gearbox mounted hydraulic starter motor. It is driven by fluid from an APU mounted hydraulic pump, or a hand pump and accumulator arrangement.

• Advantages

• Compact in size

• Can be self-contained for smaller engines

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Hydraulic

• Can be adapted to function as a pump

• Relatively uncomplicated

• Disadvantages

• Requires external power for large engines or for continuous cranking (internal APU may be used).

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8. Hand starter

• Advantages• Very reliable• Independent of external power systems,

except muscle power• Light weight• Disadvantages• Limited to very small engines• Cranking handle must be stored

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GTE Ignition Systems

• General

• Types

• Igniter plugs

• Control circuits

• Maintenance and inspection practices of turbine engine ignition systems

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GTE Ignition Systems--General

• Turbine engine ignition systems are operated for a short period of time during engine-starting only. Therefore the total operating time is insignificant compared with reciprocating engine ignition systems. For this reason, the turbine engine ignition systems are almost trouble -free.

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GTE Ignition Systems--General

• The systems also provide a standby protection against in-flight flameout which might occur at takeoff, landing & bad weather operation.

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Types

• There are two main types of turbine engine ignition systems: Capacitor-type ignition system and electronic type ignition system.

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Types

• Capacitor-type (capacitor-discharge) ignition system

• Most gas turbine engines are equipped with a high heat-intensity intermittent duty, capacitor-type ignition system.

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Types

• There are two common classifications of the capacitor ignition systems ;the high voltage and low voltage systems. Both draw sufficiently high current to cause heat damage to their units, so they have a restricted duty cycle of certain time duration, followed by a cooling-off period.

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Types

• They are designed to use either direct current or alternating current as input power.

• DC operated systems receive their power from the battery bus, and AC systems are powered from the aircraft AC bus.

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Low voltage ignition systems

• They are two types: Intermittent duty and extended (continuous) duty

• The output voltage -low tension ignition

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Low voltage ignition systems

• System is in the range of two to seven Kilo volts.

• It has the following main parts: Radio Noise filter, Audio frequency filter, Vibrator assembly (AF the input in DC), One transformer, Rectifier, Storage capacitor, bleed resistor, discharge air gap tube (spark gap), Igniter plug.

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Continuous-duty ignition systems

• It has the same main parts like intermittent duty but its operation is continuous.

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• The extended duty units are generally thought of as having a maximum of 4 joules output with no time restriction to their operation or maximum of 8 joules with a typical 30 minutes on, 30 minutes off cycle time.

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• Some extended duty systems, however, on very large aircraft, have as high as 16-20 joules of stored energy available in their capacitors, but they are still considered to be of low tension because the energy needed by a new igniter plug to fire correctly is only approximately 2 joules.

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High voltage ignition systems

• This system incorporates the high tension, intermittent duty, AC input system which is used by most turbine engines.

• The output voltage is in the range of 14 to 28 Kilo volts.

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• The high tension spark created by this type system is needed to blast carbon deposits from the igniter plug electrodes, and vaporizes fuel globules of the air-fuel mixture in the combustor either on ground or in flight.

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• It has the following basic parts:- Radio noise filter, vibrator assembly ( it in part is DC) Power transformer, Full wave rectifier, voltage doublers, storage capacitor, Gap discharger tube (spark gap), Trigger transformer (high voltage transformer), bleed resistor & trigger capacitor, igniter plugs.

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Electronic-type ignition systems

• Electronic-type ignition system is a variation of the simpler capacitor-

type system.

• In this system transistors have replaced the mechanical units of

capacitor-type system.

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System components

• Ignition exciter

• Ignition leads/harness

• Spark igniters/igniter plugs

• Ignition switch

• Power supply

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System components

• One/two ignition exciters on an engine

• Two igniter plugs on an engine operated/powered by separate exciters

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Igniter plugs

• Igniter plugs for gas turbine engines differ considerably from spark plugs for reciprocating engines. The gap at the igniter plug tip is much wider than that of a spark plug, since the operating pressure and temperature are much lower and the spark can arc more easily than is the case for a spark plug.

• The igniter plug electrode is designed to withstand a much higher intensity spark.

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Igniter plugs

• The igniter plug is also less susceptible to fouling because the high energy spark removes carbon and other deposits each time the plug fires. The construction material is also different because the igniter plug is made of a very high quality, nickel-chromium alloy for its corrosion resistance and low coefficient of heat expansion. The threads in many cases are also silver plated to prevent seizing. For this reason, it is many times more expensive than a spark plug.

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Igniter plugs

• Note:- Igniters for high and low voltage systems are not interchangeable and care should be taken to be sure that manufacturer recommended igniter plug is used.

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Types of igniters

Spark igniter An igniter plug which provides the high-

intensity sparkAnnular-gap igniter plug• Sometimes referred to as a “long reach”

igniter because it projects slightly into the combustion-chamber liner to produce a more effective spark.

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Types of igniters

Constrained-gap igniter plug

• It operates at a much cooler temperature because it does not project into the combustion chamber liner. This is possible because the spark occurs beyond the face of the combustion chamber liner.

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Types of igniters

Glow plug igniter

• Some smaller engines incorporate a glow plug type of igniter rather than a spark igniter. This glow plug is a resistance coil of very high heat value and is said to be designed for extremely low temperature starting.

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Maintenance and inspection practices of turbine engine

ignition systems

General

• Turbine engine ignition systems must be handled with extreme care because the high voltage can be lethal.

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ignition systemsIgnition system leads

• Maintenance of the typical turbine engine ignition system consists primarily of inspection, test, trouble-shooting, removal, and installation.

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ignition systems• Before disconnecting the lead from an

exciter or igniter, make sure to pull the ignition power circuit breaker.

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ignition systems• Disconnect the power lead to the exciter

and observe the time specified in the engine maintenance manual before removing the igniter lead. This time, normally about five minutes, allows energy stored in the capacitor to bleed safely to ground through the bleeder and safety resistors.

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ignition systems• Ground the center conductor of the

ignition lead to the engine to ensure that the capacitors are completely discharged after the removal of the lead from the igniter.

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ignition systemsIgniter plugs

• Igniters should be removed from the engine with extreme care and examined according to the instructions in the engine service manual.

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ignition systemsExciters

• Exciters are sealed units and cannot be

opened for servicing.

• Some exciters contain radioactive material. Necessary precautions must be taken during handling.

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ignition systems• Always refer to the applicable

manufacturer’s instructions before performing any ignition system maintenance.

The inspection of the ignition system may include the following:-

• Security of components, bolts, and brackets

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ignition systems• Shorts or high-voltage arcing

• Loose connections

• Conditions of ignition system leads

• Conditions of igniter plugs

Aircraft Engine Starting and Ignition Systems Solomon Bezuneh

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