Ignition Magneto - Aviation

Aviation

Because it requires no battery or other source of energy, the magneto is a compact and reliable self-contained ignition system, which is why it remains in use in many general aviation applications.

Since the beginning of World War I in 1914, magneto-equipped aircraft engines have typically been dual-plugged, whereby each cylinder has two spark plugs, with each plug having a separate magneto system. Dual plugs provide both redundancy should a magneto fail, and better engine performance (through enhanced combustion). Twin sparks provide two flame fronts within the cylinder, these two flame fronts decreasing the time needed for the fuel charge to burn, thereby burning more of the fuel at a lower temperature and pressure. As the pressure within a cylinder increases, the temperature rises; and if there is only a single plug, the unburnt fuel away from the original flame front can self-ignite, producing a separate unsynchronized flame front. This leads to a rapid rise in cylinder pressure, producing engine "knock". Higher octane fuel delays the time required for auto-ignition at a given temperature and pressure, reducing knock; so by burning the fuel charge faster, two flame fronts can decrease an engine's octane requirement. As the size of the combustion chamber determines the time to burn the fuel charge, dual ignition was especially important for the large-bore aircraft engines around World War II.