Engine knocking

Uncommon card · No. 193336

In spark-ignition internal combustion engines, knocking (also called knock, detonation, spark knock, or pinging) occurs when combustion of some of the air/fuel mixture in the cylinder results from a source other than the flame front ignited by the spark plug, in other words, when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel–air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive. Knocking should not be confused with pre-ignition—they are two separate events. However, pre-ignition can be followed by knocking. The phenomenon of detonation was described in November 1914...

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