Powerplant Systems & Components: Ignition & Starting Systems 🔊

Question 1

What is a magneto?

Answer 1

It is a self-contained AC generator driven by the engines for the purpose of ignition in a reciprocating engine

Question 2

Why are magneto ignition systems preferred over battery type ignition systems for reciprocating engines?

Answer 2

Magnetos are an independent ignition source and do not rely on battery power to provide ignition

Question 3

What can cause a reciprocating engine to continue to run when the ignition switch is in the OFF position?

Answer 3

If there is a break in the p-lead wire from the magneto to the switch, then the ignition switch cannot ground the magneto primary circuit

Question 4

What is the purpose of the condenser in a high-tension magneto electrical system?

Answer 4

To prevent arcing at the points and to hasten the collapse of the magnetic field around the primary coil

Question 5

Where is the E-gap position?

Answer 5

E-gap position is when the poles of the rotating magnet are a few degrees past the neutral position when the points begin to open

Question 6

What are the three major circuits of a high-tension magneto system?

Answer 6

The magnetic circuit, primary electrical circuit, and secondary electrical circuit

Question 7

What are the components of a high-tension magnetic circuit?

Answer 7

The magnetic circuit consists of a permanent rotating magnet, soft iron core, and pole shoes

Question 8

What happens when the primary breaker points open in a magneto?

Answer 8

Opening the points stops the flow of current in the primary coil. The magnetic field that was emitted by the primary coil collapses. As this magnetic field collapses, the flux lines that cut across the windings of the secondary coil induce a pulse of high voltage current in the secondary coil needed to fire the spark plugs.

Question 9

What is the position when the spark occurs in a cylinder?

Answer 9

The piston is a specific number of degrees before top dead center on the compression stroke

Question 10

What is a dual magneto?

Answer 10

A dual magneto incorporates two magnetos in one housing. They share a rotating magnet and cam, however they have their own sets of points, coils, and distributor blocks.

Question 11

What is the difference between a low tension and a high-tension ignition system?

Answer 11

In a high-tension system, the high voltage is generated in the magneto and flows to the plugs through high tension leads. In low tension systems, the low voltage is generated in the magneto and flows through the low tension leads to the primary winding of a transformer coil located near each spark plug. There the voltage is increased to high voltage by transformer action and is conducted to the plugs by very short high tension leads.

Question 12

When the ignition switch is in the OFF position, what is the condition of the primary circuit?

Answer 12

It is completed through the ignition switch to ground.

Question 13

What three conditions are required to fire plugs in a cylinder when the piston is in the prescribed position?

Answer 13

The magneto’s magnet poles must be in the E-gap position, the breaker points must open, and the distributor rotor must be aligned with a distributor electrode for that cylinder.

Question 14

What is a dual ignition system and what part of the system is grounded when the ignition switch is placed in the RIGHT position?

Answer 14

A dual ignition system uses two separate magnetos with the harness arranged so that each magneto fires one plug in each cylinder. If the switch is set to RIGHT, the left magneto will be grounded, preventing it from firing.

Question 15

What is internal timing of a magneto?

Answer 15

It is adjusting the breaker points to open when the poles of the rotating magnet are at the E-gap position

Question 16

What is the purpose of an impulse coupling used with a magneto?

Answer 16

The impulse coupling is used to retard the timing of the spark to after top dead center for starting the engine. It provides a momentary high rotational speed to produce a spark at low crankshaft rpm.

Question 17

What is staggered ignition timing?

Answer 17

It is the firing of one spark plug before the other. Instead of firing them simultaneously.

Question 18

What is the proper spark plug reach?

Answer 18

The proper spark plug reach is when the electrode end of the plug inside the cylinder is in the best position to achieve ignition

Question 19

Why is it important to keep track of the cylinder that spark plugs are installed in?

Answer 19

Because spark plugs can provide a lot of information about the health of a specific cylinder

Question 20

What type of ignition system is used in most turbine engines?

Answer 20

A typical turbine engine is equipped with an electronic capacitor type ignition system

Question 21

What is the function of the ignitor plugs in a turbine engine?

Answer 21

The function of the ignitor plug is to provide a discharge gap for current, which is stored in the capacitor. The discharge results in a high intensity spark which ignites the fuel-air mixture.

Question 22

When are turbine engine ignition systems normally in use?

Answer 22

The ignition system is required only for starting or restarting an engine

Question 23

What are two types of ignitor plugs?

Answer 23

Annular gap - a long reach plug that extends into the combustion chamber. Constrained gap - a short reach plug that does not extend into the chamber because the spark does not remain close to the plug.

Question 24

What is the purpose of the dual magneto configuration?

Answer 24

For redundancy and safety in case one magneto fails

Question 25

How can you tell if a starter commutator is dirty or worn?

Answer 25

An excessively noisy starter

Question 26

What does it mean when the starter relay clicks when the starter switch is placed in the START position?

Answer 26

This indicates that the supply voltage is too low to supply enough current to the relay coil to fully engage the contact points.

Question 27

What is an advantage of air-turbine starters when compared to electric starters for large turbine engines?

Answer 27

They are light weight and do not have the same cool down periods as electric starters

Question 28

Why do turbine ignitors not get carbon fouled as often as reciprocating engine spark plugs?

Answer 28

Due to extremely high rates of electrical discharge in the turbine ignitors

Question 29

What are three parts of an ignition systems of a turbine?

Answer 29

Exciter, ignition lead, ignitor

Question 30

What is the difference between a temporary magnet and a permanent magnet?

Answer 30

A permanent magnet is one that retains its magnetic properties for a long period of time. Temporary magnets also called an electromagnet are those that simply act like permanent magnets when they are within a strong magnetic field or have current flowing near them.

Question 31

What does the ignition light indicate when timing a magneto?

Answer 31

It indicates when the points are beginning to open