Ignition & Starters Flashcards
When does the ignition event take place in a four stroke engine?
During the compression stroke
3 types of ignition systems:
Battery
Magneto
FADEC
What does FADEC stand for?
Full Authority Digital Engine Control
What is FADEC?
A solid state digital electronic ignition and sequential port fuel injection system
What does FADEC monitor?
Manifold Air Pressure (MAP)
Manifold Air Temp (MAT)
Engine Speed (RPM)
Cylinder Head Temp (CHT)
Exhaust Gas Temp (EGT)
Ignition
Timing
Fuel Mixture
ECU (electronic control unit) is the heart of the FADEC system. What does it contain?
Contains two microprocessors that control two cylinders
What are the types of magnetos?
Low & High tension
Rotating Magnet
Single or Double
Flange or Base
What does a low tension magneto require?
A secondary coil for each spark plug
What does a high tension magneto contain?
Contains Both a primary and secondary coil in the magneto
(Most common)
How many degrees apart are the two north poles of a four-pole magneto?
180 degrees
What is inside of a double magneto?
One housing
One magnet
One cam
Two sets of points
2 coils (primary & secondary)
2 capacitors
2 distributors
What are the three magneto circuits?
Magnetic
Primary
Secondary
What is a magneto’s permanent magnet made of?
Alnico
Aluminum
Nickel
Cobalt
Where is the ignition switch found?
In the primary circuit
The direction of the magnetic lines of flux is. always from ______ to ______ pole
North to South
What is a Keeper?
A laminated soft-iron bar placed across the poles of the rotating magnet to reduce the loss of magnetism
In magneto operational theory:
As speed increases…..
Voltage output increases
What are the 3 magnet rotational positions?
Full Register
Neutral
E-gap
What is Full Register?
The position of the magnet when all of the lines of flux are passing through the coil core
What is the Neutral position?
The position of the magnet when no lines of flux are passing through the coil core
Where does the rotating magnet pass through?
The E-gap position
How many turns of large insulated copper wire are in the Primary Circuit?
Relatively few
How many turns of very fine insulated copper wire are in the Secondary Circuit?
Several thousands
The magnetic field, caused by the primary current, collapses when the breaker points open. As this field collapses, what happens?
It induces a voltage in the secondary winding of the magneto coil
When do the breaker points in a high-tension magneto open?
When the rotating magnet is in the E-gap position
What is E-gap?
The position of the rotating magnet that is rotationally a few degrees beyond neutral
What is the Cam Follower?
A plastic device that contacts the breaker points to open them
What does cam follower wear cause?
Causes the timing to drift late or retard the spark
What is the compensated cam?
Has a separate cam lobe for each cylinder due to the elliptical path that the link rods follow
What does the capacitor do?
Acts as a storage chamber to absorb the sudden rise of voltage in the primary coil when the points begin to open
What does the capacitor prevent?
Prevents arcing between the contact points
(Burned points = Bad capacitor)
How do you remove grease or carbon tracks?
Acetone and lint-free cloth
The distributor gear always turns at _____ of the engine crankshaft speed.
1/2
What do the numbers on the distributor block show?
The magneto sparking order
NOT the firing order of the engine
What is Flash over?
Arcing across the incorrect path or surface
How can flashover due to high altitude flight be eliminated?
Pressurized magnetos
What is coming-in speed?
The slowest speed that the magnet can turn and still produce an intense spark at the spark plugs
What is the Magneto Safety Gap?
Used to discharge the secondary coils’ voltage if an open occurs in the secondary circuit
(Protects the coil)
When performing a magneto internal timing, what are you determining and setting?
The correct number of degrees beyond neutral
(E-gap)
What do properly operating points look like?
Fine grained frosty or silvery appearance
Increasing the breaker point gap will do what?
Advance the spark and decrease its intensity
How do you use a timing magneto?
Connect a timing light to both magnetos and adjust until both magneto points open simultaneously
Why does the starter spark occur late?
To prevent engine kickback
What does impulse coupling do?
Provides a hot & late spark
What does the booster coil require?
Battery power
What does the second electrode or trailing finger do?
Distributes the output of the booster coil
What does the “shower of sparks” do?
Provides both a hot & late spark
What is the standard terminal end size?
5/8 - 24
What is the all-weather terminal end size?
3/4 - 20
How do you eliminate capacitance afterfiring?
With resistor type spark plugs
What is the function of a spark plug?
To conduct a short impulse of high-voltage current through the wall of the combustion chamber to ignite the fuel/air charge
What are the 3 major parts of a spark plug?
-Electrodes
-Ceramic or silicone insulator
-Metal shell
What do resistor type spark plugs do?
(Besides eliminate capacitance afterfiring)
Reduce the burning & erosion of the electrodes in engines having shielded harnesses
What are the 2 sizes of spark plug shell threads?
14mm or 18 mm (most common)
What is spark plug reach?
The threaded portion of the spark plug
What is spark plug heat range?
The ability to transfer heat from the firing end of the spark plug to the cylinder head
What are the rules for spark plug heat range?
Hot running engine = Cold spark plug
Cool running engine = Hot spark plug
What might happen if a cold plug is installed in a cool running engine?
The tip of the plug will collect unburned carbon and cause it to foul the plug
A spark plug with too large of a gap will cause what?
Hard starting
When are spark plugs considered to be worn out?
When their electrodes have worn away to approximately 1/2 of their original dimensions
What are the 3 main components of a turbine ignition system?
-Exciter box
-Ignition leads
-Igniters
Gas-turbine ignition systems are required to:
Operate for starting only
What are turbine ignition systems rated in?
Joules
Reciprocating engine ignition systems are rated in what?
Volts
What is another name for transformer units?
Exciter box
In the low-tension DC input system, what holds the points closed when the cockpit switch is off?
A Permanent Magnet
In the low-tension DC input system, what is the purpose of the bleed resistor?
To allow the capacitor to bleed off its charge when the system is de-energized
In the high-tension AC input system, what is not required because the system uses alternating current?
A Vibrator
(This eliminates the problems associated with the use of vibrating contacts)
In the high-tension AC input system, what is the name of the transformer that steps the 4,000 V DC to 20,000 V DC prior to the igniter?
The Trigger Transformer
What are the 4 parts of an igniter?
-Insulators
-Electrodes
-Shell body
-Internal seals
Since the igniter usually operates just long enough to start the engine, what happens?
The total erosion over a long period of engine operation is not great.
What are the 3 types of igniter plugs?
-Low voltage
-High voltage
-Glow plugs
(High, Low, Glow)
What are 2 types of low voltage igniter plugs?
-Shunted surface gap (parallel or across)
-Glow coil element
What are 4 types of high voltage igniter plugs?
-Air surface gap
-Surface gap
-Recessed surface gap
-Constrained gap
The constrained gap igniter plug used in some gas turbine engines operates at a cooler temperature because:
The construction is such that the spark occurs beyond the face of the combustion chamber liner
The capacitor type ignition system is used almost universally on turbine engines because of its:
High voltage and high heat intensity
What is the most common type of magneto?
High-tension , 2 Pole
What is a magneto?
A self-contained Alternating Current generator that produces electrical pulsations of high voltage for the purpose of ignition
How do you increase Flux Linkage?
• Add more turns in the coil of wire.
• Use a stronger magnet.
• Increase the speed of the magnet.
What is Lenz’s Law?
An induced voltage always operates in such a direction as to oppose the source of its creation.
The ratio of magneto shaft speed to crankshaft speed is:
Number of cylinders
——————————
2 x number of poles
What components are in the primary circuit?
• Primary Windings.
• Breaker Points.
• Condenser (Capacitor).
• Ignition Switch.
What components are in the secondary circuit?
• Secondary Winding.
• Carbon Brush.
• Rotor.
• Distributor Block.
• Ignition Leads.
• Spark Plugs.
• The rotor and distributor block
What are the SIZES OF IGN. LEADS?
• 5MM, 7MM & 9MM
MODERN HARNESSES USE 5MM.
What is CAPACITANCE AFTERFIRING?
WHEN THE SHIELDING OF THE IGNITION LEAD STORES A CHARGE AND CAUSES THE SPARK PLUG TO FIRE OUT OF SEQUENCE.
What are the 2 TYPES OF ELECTRODES?
• FINE WIRE
• MASSIVE ELECTRODE (most common)
Why should you PLACE EACH SPARK PLUG IN A TRAY WITH NUMBERED HOLES?
THE CONDITION OF THE PLUG WILL INDICATE THE CONDITION OF THE CYLINDER.
What are the 4 BASIC TYPES OF ENGINE STARTERS for reciprocating engines?
• HAND PROPPING
• DIRECT CRANKING (ELECTRIC)
• INERTIA (FLYWHEEL)
• COMBUSTION (EXPANDING GAS)
What are the 4 types of starters for turbine engines?
- DIRECT CRANKING (ELECTRIC)
- AIR TURBINE
- COMBUSTION A.K.A .CARTRIDGE (EXPANDING GAS)
- AIR IMPINGEMENT
What are the two types of turbine starter systems?
AC &DC
