What is wasted spark ignition

Since waste sparks use almost as much energy as ignition sparks, a waste spark engine will waste almost as much fuel again! And this is just at idle! Two-stroke engines do not have wasted sparks, because they do not have an exhaust stroke. On a two-stroke engine, there is a compressed fuel-air mixture to ignite at top-dead-center on every revolution. Because the coil fires the spark plug on the exhaust stroke as well, it is appropriately named 'wasted spark ignition'. In effect, the spark plugs fire simultaneously and twice as often.

One of the two paired spark plugs is always negative polarity while the other spark plug is always positive polarity. Negative polarity means the spark plug's center electrode is negatively charged and its ground electrode is positively charged.

Positive polarity is the opposite. The earliest DIS featured a bank of coils; one coil for every two cylinders. Each pair of coils would provide power to two spark plugs. Each of the two paired coils would fire the paired spark plugs simultaneously, one on the compression stroke and the other on the exhaust stroke.

It is important to know that in a waste spark ignition system that spark plug electrode wear occurs differently based on the polarity.

The ignition module, located in the ECM or in the coil itself, controls on-time dwell. Limiting the amount of dwell reduces unwanted heat when demand is low but still provides full saturation for acceleration, a heavy load, and passing.

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