It have to: 1) stay cool enough to prevent pre-ignition 2) stay hot enough to burn off combustion deposits 3) provide spark to ignite A/F mixture. Spark plug is passive component with 3 basic functions. However engine knock sensor is often not working properly, or is purposely eliminated on some performance applications, which exposes engine and spark plug to damage from severe detonation. Modern engines are equipped with a Knock Sensor which provides feed back to engine ECU/PCM to adjust engine ignition timing in order to prevent prolonged detonation. However prolonged and severe detonation will hurt the engine and the spark plug, and is probably the most common cause of failure due to inconsistency of the octane rating of gasoline. They use knock sensors to "listen" for the pinging and retard the timing accordingly. Modern engines in order to reach the maximum fuel economy run on the edge of pinging. Detonation (can be also heard as engine knock or pinging) is not necessarily damaging to the engine if it is not prolonged and only very small amount of un-burnt mixture detonate. Pre-ignition will destroy the engine, put hole trough the piston, or even blow it up. Pre-ignition is far more destructive to the engine than detonation because maximum cylinder pressure is reached far before the piston reach the TDC (top dead center). Please note that detonation is a different event than pre-ignition where the mixture is ignited by usually hot spot, glowing carbon deposit or overheated ground spark plug electrode, prior to the mixture ignition by spark form spark plug. The damage to the spark plug is a result of the events and the high frequency shock wave. This event takes place in a split second and cause extreme pressure shock wave, which often pits the piston surface (looks sandblasted as it compresses less dense micro-portions of the aluminum alloy) and almost always breaks ceramic insulator on the spark plug. As the flame front propagate trough the combustion chamber, the pressure and heat on the remaining yet un-burnt mixture increases dramatically pass the point of fuel octane rating and any hot spot (most often hot side of the piston) will detonate (explode) the remaining yet un-burnt mixture. These terms are commonly misunderstood and confused with each other.ĭetonation occurs after normal combustion (controlled burning) was initiated from a spark between spark plug electrodes. The two most destructive combustion events to the engine and the Spark Plug are: PRE-IGNITION and DETONATION. Spark plug is like a dipstick into your engine, which will let you see what is going on inside of the combustion chamber. Excessive formation of combustion depositsĭust penetration into the combustion area
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