The ignition system is designed to ignite the air-fuel mixture in each cylinder at a certain point in time. In gasoline engines, this is achieved by an electric spark (electrical discharge), created between the electrodes of the spark plug.
Reliable ignition performance throughout the engine operating range is essential for the efficient operation of a catalytic converter.
Ignition by a spark of a small cloud of a finely dispersed air-fuel mixture is sufficient to start the combustion process.
The spark plug determines the length of the spark, which also depends on the type and design of the ignition system, as well as the conditions under which ignition occurs.
For a spark to occur, the voltage between the electrodes of the spark plug must rise sharply from zero to the voltage required to form an arc. After the spark discharge occurs, the voltage drops to the level necessary for the spark to propagate, and the air-fuel mixture is ignited.
To obtain the energy of sparking, an ignition coil is used, which operates on the principle of an autotransformer and accumulates the ignition energy. When current is applied to the primary winding of the ignition coil, the current energy is converted into the energy of the magnetic field until the current is stopped. At the same time, the magnetic field sharply decreases, inducing a high voltage current in the secondary winding of the ignition coil, which flows through high-voltage wires to one spark plug.
Approximately 2 ms elapses between the initial moment of ignition of the working mixture and its complete combustion. Therefore, spark generation must occur before the piston reaches TDC, which ensures optimal combustion over the entire engine speed range. The ignition timing is determined depending on the crankshaft speed, load, engine design features, fuel quality and current operating conditions (starting, idling, throttle opening, etc.).
The spark plug serves to transfer the high voltage current generated in the ignition coil to the electrodes in the combustion chamber, where this current produces a spark discharge to ignite the working mixture.