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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.
Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events.
Pressure in cylinder pattern in dependence on ignition timing: (a) - misfire, (b) too soon, (c) optimal, (d) too late. In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke.
Spark plug with single side electrode An electric spark on the spark plug. A spark plug (sometimes, in British English, a sparking plug, [1] and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing combustion pressure within ...
A fourth problem can arise when one or more of an engine's spark plugs becomes "fouled." Fouling, caused by combustion-byproducts that form deposits on a spark plug's internal insulator, creates an electrically conductive path that dissipates the coil's energy before its secondary voltage can rise high enough to produce a spark.
The contact breaker is operated by an engine-driven cam.On an engine with a distributor, the contact breaker can be found beneath the distributor cap.The position of the contact breaker is set so that it opens (and hence generates a spark) at exactly the optimum moment to ignite the fuel/air mixture.
A wasted spark system is a type of ignition system used in some four-stroke cycle internal combustion engines. In a wasted spark system, the spark plugs fire in pairs, with one plug in a cylinder on its compression stroke and the other plug in a cylinder on its exhaust stroke. The extra spark during the exhaust stroke has no effect and is thus ...
Since the CDI system provides only a reduced duration spark, it's also possible to combine this ignition system with ionization measurement. This is done by connecting a low voltage (about 80 V) to the spark plug, except when fired. The current flow over the spark plug can then be used to calculate the temperature and pressure inside the cylinder.