The aircraft engine is a powerful apparatus, enabling the generation of propulsion that allows for flight to be possible. For an engine to begin operation, it requires ignition for the combustion of fuel mixtures and other processes. While the aircraft ignition system may differ from aircraft to aircraft, they all share various common components and processes that are critical for their functionality. In this blog, we will discuss the composition of the aircraft ignition system, helping you to better understand how engines are started and function.
In general, an ignition system engine will consist of magnetos, spark plugs, an ignition switch, a source of electricity, solenoids, starter motors, and various wires that connect the system together. The magneto is a type of electrical generator that provides periodic alternating current pulses through the use of permanent magnets, and they supply the engine spark plugs with electricity for ignition. Magnetos operate from the engine electrical system, thus are independent from the rest of the aircraft. For their operation, a magneto begins firing when the starter is engaged, and it continues to fire while the crankshaft rotates. Generally, an aircraft will have two magnetos and four spark plugs, and each magneto will supply current to one of the two spark plugs that are present within each engine cylinder. The aircraft spark plugs are what allows for fuel air mixtures to be combusted, and they do so by providing a short impulse of electric current that is passed through the combustion chamber walls. While spark plugs are simple in design, they are often one of the most important components as without proper functionality, an engine will be unable to function.
Magneto ignition is controlled by the ignition switch, located within the flight deck for pilot operation. The ignition switch has multiple positions that may be used depending on the need, and these include OFF, R (right), L (left), BOTH, and START. With the use of the right or left position, a pilot can individually operate each magneto as needed, while the BOTH option allows for simultaneous operation. During preflight checks, pilots will often monitor the RPM of the engine while switching the ignition switch from BOTH to RIGHT, and then BOTH to LEFT. if there is an RPM value below allowed limits, or the engine stops operating while selecting a single magneto, an issue may be present that should always be addressed before continuing operations.
Across aircraft types, many modern models have a starter that is capable of automatically engaging and disengaging during operation, though some models may require the pilot to manually operate a lever for starting the engine. When the starter is engaged, it actuates the flywheel, causing the engine to revolve at a speed that allows for proper operation. The power needed to actuate the starter is typically provided through a battery of the engine electrical system, though some starters may require external power. To properly conduct the starting procedure of the aircraft ignition system, one should always follow basic safety rules and manufacturer recommendations.
If all parts of the aircraft ignition system engine are functioning properly, then combustion should occur in a predictable manner that is consistent. Generally, magneto ignition with the spark plugs should be instantaneously, and temperature and pressure should be built up smoothly. If there is abnormal combustion, such as uncontrolled detonation or pre-ignition, the aircraft should not be operated until the issue is addressed.
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