Designed to limit energy loss between the coil and the spark plugs, these operate without high tension leads and mounted directly on the spark plugs, taking advantage of restricted space and independent high-voltage source for each cylinder. In modern car, single spark technology is more popular for automotive manufacturers.
Four types of coil-on-plug
1.\tCoil-on-plug with single spark technology
(1) Pencil coil (the high-voltage transformer is in the coil head, also called compact coil).
Design of plug to coil as known as single spark ignition coils, which generate one ignition spark per power stroke, therefore they must be synchronized with the camshaft.
(2)\tPencil coil (The high-voltage transformer is in the cylindrical coil body)
2. Coil-on-plug (with wasted spark design) With double spark technology