General information about the ignition system [Toyota RAV4 XA10]

The ignition system is designed to ignite the fuel-air mixture in each cylinder at a specific point in time. In gasoline engines this is achieved by an electric spark (electric discharge), created between the spark plug electrodes.

Reliable ignition operation throughout the entire engine operating range is an essential factor for the efficient operation of the catalytic converter.

Ignition of a small cloud of finely dispersed fuel-air mixture by a spark 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 spark plug electrodes must increase sharply from zero to the voltage required to form an arc. After the spark discharge occurs, the voltage drops to the level required for the spark to propagate, causing the fuel-air mixture to ignite.

To obtain spark energy, an ignition coil is used, which operates on the principle of an autotransformer and accumulates ignition energy. When current is applied to the primary winding of the ignition coil, the energy of the current is converted into the energy of the magnetic field until the current supply is stopped. The magnetic field is then sharply reduced, inducing a high voltage current in the secondary winding of the ignition coil, which flows through the high voltage wires to one spark plug.

Approximately 2 milliseconds elapse between the initial ignition of the fuel mixture and its complete combustion. Therefore, spark generation must occur before the piston reaches TDC, ensuring optimal combustion across the entire engine speed range. The ignition timing is determined depending on the crankshaft speed, load, engine design features, fuel quality and operating conditions at the current moment (starting, idle speed, throttle opening, etc.).

The spark plug is used to transmit 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.