Ignition

The electric ignition system is, at the moment, the last recognising sign of the petrol engine. It has the task of igniting the fuel- air mixture under all working conditions, so that the pressure increase occurs shortly after TDC. Whereby, the igntion should occur as early as possible, by no means however, too early, this would cause a spontaneous combustion and thus, knocking. Nowadays, the ignition point is mostly electronically regulated, either for the values of each operational condition (characteristic map) or through supervision e.g., by a knocking sensor.

The production of an electric arc in the spark-plug is called induced ignition. This is made possible by the conversion of 12V-DC into, generally, more than 10.000V of high tension. The necessary energy (see picture) is provided either by the battery, (starting) the generator (running engine) or by a permanent magnet. To reach the high tension, a transformer is also necessary (mostly in stand-by mode). In multi-cylinder engines, there is an exactly defined firing order, which not only depends on the amount of cylinders, but also on their layout. Modern ignition coils are either linked individually to each cylinder or to two of them.

The forerunners of todays ignition are, the glow-pipe, the buzzer and the magneto ignition, from which only the latter is still able to hold its own. The electronic ignition is partly responsible for the decontamination of the exhaust gasses and for the prevention of CO₂-emission. It has become an integral part of the engine management. On the outside, only components such as the ignition coil and the spark plug are recognisable. In the meantime, even these are being used as sensors, thus substituting e.g., for the knocking sensor.

To generate an electric arc, a tension distinctly higher than that of the battery is necessary. This is achieved through induction. Induction always occurs at the ends of a conductor then, when it is moved through an electrically or magnetically built up field. The word itself, comes from the Latin verb 'inducere' and means as much as 'to lead in'. Apart from in the ignition coil, one can observe induction also in any relay, the inductive sensor or in the generator.

One calls wound around, mutually insulated wire a coil, it generally makes no difference whether the coil is moved against a permanent magnet or vice versa. One can also move a current carrying coil against one not supplied with tension, a tension is always measurable on the latter, whose plus-/minus alignment is dependent on the direction of movement through the energy-field. 02/10