Automotive

1 Ignition system

The ignition system of an internal−combustion engine is an important part of the overall engine system. It provides
for the timely burning of the fuel mixture within the engine. Not all engine types need an ignition system − for
example, a diesel engine relies on compression−ignition, that is, the rise in temperature that accompanies the rise in
pressure within the cylinder is sufficient to ignite the fuel spontaneously. All conventional petrol (gasoline) engines,
by contrast, require an ignition system.
1.1 Contact ignition
The earliest petrol engines used a very crude ignition system. This often took the form of a copper or brass rod
which protruded into the cylinder, which was heated using an external source. The fuel would ignite when it came
into contact with the rod. Naturally this was very inefficient as the fuel would not be ignited in a controlled manner.
This type of arrangement was quickly superseded by spark ignition, a system which is generally used to this day,
albeit with sparks generated by more sophisticated circuitry.
1.2 Glow plug ignition
Glow plug ignition is used on some kinds of simple engines, such as those commonly used for model aircraft. A glow
plug is a coil of wire (made from e.g. nichrome) that will glow red hot when an electric current is passed through it.
This ignites the fuel on contact, once the temperature of the fuel is already raised due to compression. The coil is
electrically activated for engine starting, but once running, the coil will retain sufficient residual heat on each stroke
due to the heat generated on the previous stroke. Glow plugs are also used to aid starting of diesel engines.
1.3 Magneto system
The simplest form of spark ignition is that using a magneto. The engine spins a magnet inside a coil, and also
operates a contact breaker, interrupting the current and causing the voltage to be increased sufficiently to jump a
small gap. The spark plugs are connected directly from the magneto output. Magnetos are not used in modern cars,
but they are often found on mopeds, with 2−stroke engines and also in aircraft piston engines, where their simplicity
and self−contained nature confers a generally greater reliability as well as lighter weight. Aircraft engines usually
have multiple magnetos to provide redundancy in the event of a failure.
1.4 Mechanical ignition
Most four−stroke engines have used a mechanical ignition system. Here, the power source is a lead−acid battery,
kept charged by the car's electrical system, which generates electricity using a dynamo or alternator. The engine
operates contact breaker points, which interrupt the current flow to an induction coil − a form of autotransformer.
This steps up the voltage, which is fed via a rotating switch called a distributor to the spark plugs. This sytem is not
greatly different from a magneto system, except that more separate elements are involved. There are also
advantages to this arrangement, for example, the position of the contact breaker points relative to the engine angle
can be changed a small amount dynamically, allowing the ignition timing to be automatically advanced with
increasing revolutions per minute (RPM), giving better efficiency. This system was used almost universally until the