Why Does a Spark Plug Exhibit Corona Phenomenon?

[StIsabela]

Spark plugs exhibiting corona phenomenon indicate prolonged usage, which can lead to poor sealing and reduced engine power. Timely replacement is recommended. The functions and precautions for spark plugs are as follows: Functions of Spark Plugs: The spark plug's role is to introduce the high-voltage electricity generated by the ignition coil into the engine cylinder, creating a spark across the electrode gap to ignite the air-fuel mixture. Precautions for Spark Plug Usage: When disconnecting the high-voltage lead, handle it gently. Avoid forcefully shaking the spark plug insulator during operation, as this may compromise the spark plug's sealing performance. Only remove the spark plug after the engine has cooled down. Before unscrewing the spark plug, use a thin, soft tube to clean any debris around it to prevent contaminants from falling into the combustion chamber upon removal.

[McRiley]

I've seen quite a few cases of spark plug corona discharge, which is mainly caused by sealing issues. If you look closely at the ceramic part of the spark plug, you'll notice brownish marks, right? That's a sign of high-voltage leakage. The most common reason is incorrect torque during installation - too loose causes gas leakage, while too tight crushes the ceramic. Another cause is excessive oil contamination in the engine bay or high humidity on rainy days, where dirt adheres to the ceramic and forms a conductive path, diverting the electricity. In some older cars, deteriorated or deformed rubber gaskets on the spark plugs can also reduce sealing performance and lead to this issue. Don't underestimate corona discharge - it weakens ignition energy, making the car feel sluggish and increasing fuel consumption. In such cases, it's recommended to reinstall or replace the spark plugs entirely. Remember to clean off any surrounding oil contamination and use a torque wrench to tighten them according to the manufacturer's specifications.

[TannerDella]

A while ago, my car was shaking badly, and upon inspection, it turned out to be a spark plug corona issue. Simply put, corona occurs when high-voltage electricity doesn't jump properly from the center electrode but instead leaks along the ceramic insulator, leaving a yellowish-brown mark. There could be several reasons for this: first, improper cleaning during installation, where sweat or dust on the ceramic creates a leakage path; second, excessive moisture in the engine bay, which worsens the leakage; and third, using the wrong spark plug model, where a mismatched heat range causes uneven heat dissipation. When I handled it myself, I noticed the old spark plug's rubber seals had deteriorated, so I replaced them with new NGK plugs of the same model, thoroughly cleaned the ignition coil contacts with anhydrous alcohol, and haven't had any issues for three months since installation.

[Jimmy]

Corona discharge is essentially an insulation failure. The ceramic insulator in the center of a spark plug is designed to isolate high voltage electricity, but when contaminated with oil or carbon deposits, it becomes conductive, allowing the high voltage to leak along the ceramic surface, forming brownish traces. This commonly occurs in two scenarios: first, when the ceramic insulator is slightly cracked by wrench contact during installation; second, when the engine cylinder head is uneven, causing the spark plug to tilt. It is recommended to choose iridium spark plugs with anti-fouling coatings to reduce contamination. Always wear gloves during installation to avoid contaminating the ceramic insulator, and check the elasticity of the sealing ring during each maintenance. While it may not affect driving in the short term, prolonged leakage can shorten the lifespan of the ignition coil.