This system only passed a very low current through the ignition points, using a PNP transistor to perform high-voltage switching of the ignition current, allowing for a higher voltage ignition spark, as well as reducing variations in ignition timing due to arc-wear of the breaker points. In mid-1963, Ford offered transistorized ignition on their new 427 FE V8. This typically applies to automotive use marine gasoline engines generally use a similar system but without vacuum advance. Many of these engines will also use a vacuum advance that advances timing during light loads and deceleration, independent of the centrifugal advance. The distributor's centrifugal timing advance mechanism makes the spark occur sooner as engine speed increases. Spark timing, relative to piston position, is based on static (initial or base) timing without mechanical advance. The spark ignition system of mechanically controlled gasoline internal combustion engines consist of a mechanical device, known as a distributor, that triggers and distributes ignition spark to each cylinder relative to piston position-in crankshaft degrees relative to top dead centre (TDC). Usually, any major engine changes or upgrades will require a change to the ignition timing settings of the engine. These include the timing of the intake valve(s) or fuel injector(s), the type of ignition system used, the type and condition of the spark plugs, the contents and impurities of the fuel, fuel temperature and pressure, engine speed and load, air and engine temperature, turbo boost pressure or intake air pressure, the components used in the ignition system, and the settings of the ignition system components. There are many factors that influence proper ignition timing for a given engine. Older engines that use mechanical distributors rely on inertia (by using rotating weights and springs) and manifold vacuum in order to set the ignition timing throughout the engine's RPM and load range.Įarly cars required the driver to adjust timing via controls according to driving conditions, but this is now automated. Modern engines that are controlled in real time by an engine control unit use a computer to control the timing throughout the engine's RPM and load range. Many variables also affect what the "best" timing is. The ignition timing affects many variables including engine longevity, fuel economy, and engine power. Sparks occurring too soon or too late in the engine cycle are often responsible for excessive vibrations and even engine damage. Setting the correct ignition timing is crucial in the performance of an engine. Sparks occurring after top dead center (ATDC) are usually counter-productive (producing wasted spark, back-fire, engine knock, etc.) unless there is need for a supplemental or continuing spark prior to the exhaust stroke. Advancing the spark BTDC means that the spark is energized prior to the point where the combustion chamber reaches its minimum size, since the purpose of the power stroke in the engine is to force the combustion chamber to expand. In a vast majority of cases, the angle will be described as a certain angle advanced before top dead center (BTDC). The combustion gases take a period of time to expand and the angular or rotational speed of the engine can lengthen or shorten the time frame in which the burning and expansion should occur. The need for advancing (or retarding) the timing of the spark is because fuel does not completely burn the instant the spark fires. 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. Pressure in cylinder pattern in dependence on ignition timing: (a) - misfire, (b) too soon, (c) optimal, (d) too late. JSTOR ( January 2017) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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