Does the Spark Plug Work Continuously?

[Terrence]

The spark plug works continuously. The function of the spark plug is to discharge the pulsed high-voltage electricity sent by the high-voltage wire, break down the air between the two electrodes of the spark plug, and generate an electric spark to ignite the mixed gas in the cylinder. Its characteristics include high-energy stable sparks, uniformly mixed gas, and high compression ratio. Spark plugs are divided into: 1. Standard spark plug: The insulator skirt is slightly retracted into the shell end face, and the side electrode is outside the shell end face; 2. Insulator-protruding spark plug: The insulator skirt is longer and protrudes outside the shell end face; 3. Fine-electrode spark plug: The electrode is thin, characterized by strong sparks and good ignition capability.

[Palacios]

I also used to think that spark plugs worked continuously, but later I learned that they actually operate intermittently like a metronome. In a four-stroke engine, the spark plug only fires for a brief moment at the end of the compression stroke, with each ignition lasting about one-millionth of a second. The rest of the time, it's idle, waiting for the piston to complete the intake, compression, and exhaust strokes before the next ignition. So, when the engine runs at 3000 RPM, it has to ignite the air-fuel mixture 15,000 times per minute, with only 0.02 seconds between each ignition. This intermittent operation actually extends its lifespan, typically lasting up to 80,000 kilometers. However, during rapid acceleration, the ignition frequency spikes, making the spark plug electrodes more prone to carbon buildup. I just cleaned the carbon deposits in my car last week, so I recommend checking the gap size regularly.

[DelBeckett]

When I first started driving, I also wondered if spark plugs were on standby 24/7. In reality, their working rhythm is completely synchronized with the engine cycle: they only fire once every two crankshaft rotations, and each ignition lasts just the duration of a spark. Especially at idle, you can distinctly feel the longer intervals between ignitions—at this point, the spark plugs are practically in a semi-dormant state. But when you floor it to overtake and the tachometer needle suddenly jumps to 5000 RPM, they have to fire 25,000 times per minute, like a machine gun. This high-stress condition can easily cause the insulating ceramic to crack—my neighbor’s car once broke down mid-drive because of this. So during every maintenance check, it’s best to test the ignition coil voltage; a stable 9V-12V ensures the spark plugs don’t retire prematurely.

[Melanie]

Spark plugs work like precision fireworks, igniting only when needed. Each cylinder's spark plug releases a spark precisely when the compressed air-fuel mixture reaches its limit, a process lasting just 0.3 milliseconds. During daily driving, idling at red lights requires about 700 ignitions per minute, while highway cruising surges to 4,000. However, frequent short trips are most damaging - cold starts allow cylinder moisture to crack the ceramic insulator, which forced me to replace all spark plugs in my old car. Remember, long-distance driving is actually gentler on the ignition system.