• Coil on plug
• Waste spark
In the coil on plug system, each spark plug will have its own individual coil that sits right on top of it. This is a so called Direct Ignition module.
In a waste spark system, the two spark plugs will share the same coil. So therefore, in this system both spark plugs are attached to the coil and they are fired simultaneously. While one cylinder is toward the end of its compression stroke, its piston pair is nearing the end of the exhaust stroke, and both plugs are then fired.
Even though the spark plugs are manufactured exactly the same, if they are re-installed after there has been some extended use, they should then go back into the cylinder from which they came from. The reason for this is because the electrons will align themselves favorably with one direction of current flow. While the one plug will receive positive potential (voltage) at the wire side, the piston pair will receive the negative potential. The negative potential is what causes the second plug to fire instead of the voltage just going straight to ground after firing the first one. Vehicles seem to use the conventional theory as opposed to the electron theory of current flow.
The waste spark system is better than having a single coil, and it is cheaper than having a coil on plug. The disruptive discharge tesla coil is an earlier coil of the ignition coil in the ignition system. It also used the same principles of the ignition coil that is used in today’s vehicles.