Engine Ignition Systems

• The ignition system is a critical component in combustion engines.
• Spark-ignition engines require a system to ignite the compressed fuel-air mixture.
• The function of the ignition system is to generate an electrical spark that ignites the fuel/air mixture in the cylinders.
• The engine's ignition system is separate from the airplane's electrical system.
• The ignition timing occurs inside the cylinder at the conclusion of the compression stoke.
• The ignition system is part of the electrical system, responsible for delivering the electrical current to the spark plugs at the correct time, to ignite the air-fuel mixture.

Types of Ignition Systems

• Battery Ignition System
• Magneto Ignition System

Battery Ignition System

• Operates with a battery charged by an engine-driven generator.
• A cam, rotated by the engine disrupts the flow of current in the primary circuit.
• The collapsing magnetic field induces a high voltage at the ignition coil.

Magneto Ignition System

• Uses a magneto for the generation of electricity.
• Magnetos are mainly used on reciprocating aircraft engines.
• Magnetos are self-contained, engine-driven units that supply electrical current without using an external source of current.
• Aircraft batteries provide the electrical power initially to operate the starter which turns the engine crankshaft to start the engine.
• The starter actuates the armature of the magneto to produce ignition sparks for each cylinder.
• Once the engine is running, the starter system is disengaged.
• The battery no longer contributes to the engine operation.
• Modern airplane engines require a dual ignition system comprised of two separate magnetos.
• A dual ignition system is used to supply electric current to two spark plugs in each cylinder.
• One magneto system supplies current to one set of spark plugs, with the second magneto system supplying the other set.
• Dual ignition systems provide increased safety and more complete combustion, leading to improved engine performance.

Battery Ignition System vs Magneto Ignition System

• Battery Ignition System requires a battery for starting, while Magneto Ignition System does not need a battery.
• Battery Ignition System is harder to start if the battery is discharged, while the Magneto Ignition System has no issues with battery discharge.
• Battery Ignition System is more prone to maintenance problems due to the battery, while Magneto Ignition System is less prone to maintenance problems.
• Battery Ignition System obtains current for the primary circuit from the battery, while the Magneto Ignition System generates the electric circuit by the magneto.
• Efficiency decreases with reduced spark intensity in a Battery Ignition System, while Efficiency improves due to high-intensity spark in a Magneto Ignition System.
• The spark quality is high in Battery Ignition Systems, but the spark quality is poor during starting in Magneto Ignition Systems due to low speed.
• Battery Ignition System uses a battery for the current in a primary circuit, while a Magneto Ignition System uses a magneto to generate the required electric current.

Dual Ignition System Advantages

• Increased safety because if one system fails, the engine can run on the other to allow for a safe landing.
• Routine magneto checks are important for good operation during takeoff.
• Magneto switches should be tested according to manufacturer recommendations.
• This involves moving from "BOTH" to the farthest "ON", back to "BOTH", then to the nearest "ON," and back to "BOTH".
• Magneto switch sequence assures that the switch returns to the "BOTH" position for normal operation in flight.
• Comparison of each ignition system's performance is made in the "BOTH" position.
• Enhanced combustion is achieved, improving engine performance as the fuel mixture is ignited from both sides of combustion chamber towards the center.

Essential Parts of an Ignition System

• Magneto
• Spark Plugs
• Ignition Switch
• Ignition Harness
• Distributor

Magneto Details

• The magneto is an engine-driven electrical generator that uses permanent magnets and coils to produce high voltage.
• Aircraft magnetos are commonly used in piston aircraft engines because of its simplicity and reliability.
• The magneto generates electrical power from the engine's rotation of a permanent magnet.
• This rotation induces a current in the coil winding.
• When the current flow stops, the magnetic field collapses across a second set of windings in the coil, generating a high voltage which is used to arc across the spark plug gap.
• Magneto operation is timed to cause the spark at a specific number of crankshaft degrees before top dead center piston position.

Magneto Check

• Magneto check is an inspection of the entire ignition system.
• The magneto drop-off check is based on engine speed, it is typically done during the pre-flight inspection.
• The purpose is to determine the amount of engine speed loss when magnetos are switched from BOTH to one magneto (LEFT or RIGHT).
• It's important to refer to the appropriate operating manual for correct rpm numbers during the magneto check.
• Switch the magneto from the Both position to the R and L positions at the recommended power setting.
• Always go back to the Both position when moving the switch.
• Expect a drop in power, but it should not exceed the maximum allowable.
• Significant rpm drop could indicate issues like a fouled plug, bad ignition wire, or improper timing.

Other Magneto Check Considerations

• Have it checked by a mechanic if needed.
• No rpm drop can indicate a broken P-lead.
• Place the ignition switch to OFF to check; if the P-lead breaks, the engine continues running, and the engine will not start if the P-leads are good.
• Place the mag switch back to ON immediately if the first attempt leads to the engine beginning to halt to restart the engine.
• Improper magneto timing can cause little or no rpm drop.
• If unsure, seek professional inspection.
• The difference in rpm drop between left and right magnetos is noted.
• The operating manual specifies maximum allowable difference.
• A typical RPM drop is about 50 rpm.
• Differences between the mags' rpm can be excessive, even if within individual limits, indicating timing issues of one or both magnetos.
• Get it checked if there is any doubt or unusual readings, as a small difference could also signal a problem.
• If a magneto develops a timing issue, it could greatly affect engine performance.
• Switching to L and R positions can help determine if the engine runs better on a single magneto compared to both.
• The L and R positions of the mag switch shut off one magneto each.
• A bad mag will make the engine run badly when switched to one position, while it will run better in the other switch position.
• If necessary, continue flight to an airport for repairs on one magneto.
• The active magneto isn't overworked, and isn't negatively impacted when the partner is turned off.
• Aircraft maintenance guides provide the limits drop in RPM caused by grounding the magnetos.

Three Conditions to Satisfy When Checking Magnetos

• The magneto grounding wires are connected; If this is not completed, there will be no drop in RPM when that magneto is selected.
• The drop in RPM falls within the recommended limits in the Aircraft Maintenance Operating Handbook; Ensuring this check ensures the aircraft is capable of one magneto at reduced performance.
• The differential drop between magnetos falls within the limits the Aircraft Maintenance Operating Handbook specifies; Any large differences are demonstrating a malfunction within one of the magnetos.

Ignition Switch

• The operation of the magneto is controlled in the flight deck.
• When RIGHT or LEFT is selected, only the magneto is activated.
• BOTH uses two simultaneously.
• A malfunctioning ignition system can be detected during pre-takeoff by monitoring the decreased in rpm when the ignition switch moves from BOTH to RIGHT then BOTH to LEFT.
• The permissible decrease is listed in the AFM or POH
• Do not fly the aircraft until the issue is addressed if the engine dies when switched to one magneto.
• Do not fly the aircraft until the issue is addressed if the rpm drop surpasses established limitations, or if there is no drop detected
• The issue could be caused by fouled plugs, damaged wire, or incorrectly timed plugs.
• The ignition switch has four positions: OFF, L, R, and BOTH.
• In "L or "R" positions, only one magneto supplies current to only one set of spark plugs per cylinder.
• In the BOTH position, both magnetos supply current to both spark plugs.
• Following engine shutdown, it is important to switch the ignition switch to the OFF position.
• Even when switches are in the OFF position, the engine could start if the propeller rotated with residual fuel and the ground wire is disconected.
• If this occurs, move the mixture level to idle cutoff to stop the engine.

Ignition Booster

• This component comes in the form of a booster magneto, with high-tension coil that primary current from a battery supplies.
• The impulse coupling increases the magneto’s voltage during starting.
• Impulse coupling briefly gives high rotational speed to the rotor of magneto during starting.

Impulse Coupling

• It gives brief acceleration specifically to the one magneto attached to the left side of the engine to have an intense spark for starting.

Distributor

• It is an enclosed rotating shaft used in spark-ignition internal combustion engines that have mechanically-timed ignition.

Ignition Harness

• This is completely screened with cables and terminals; connects spark plugs of reciprocating engines and carry high-voltage current from magnetos or the electronic ignition.