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Acceleration Enrichment is a complex matter to discuss but it must be tuned to provide good engine response in transient situations. Lets say our engine is idling and we quickly stab the throttle without any acceleration enrichment. The engine will stumble and fail to immediately rev up due to insufficient fuel creating a lean condition. So why does this happen?
When an engines injector pulse width is relatively static, a film of fuel is “built” up inside the intake port. The amount of fuel this film holds varies depending on intake pressure, temperature, injector pulse with and etc. When we quickly change one of those variables the fuel film is consumed or built up. In our example above we made a quick change in the intake manifold pressure by opening the throttle quickly. This increase in manifold pressure (from vacuum to atmospheric pressure) means the fuel film can grow larger and as such a portion of the injected fuel goes into building up a larger fuel film instead of going into the cylinder for combustion. This results in a lean condition as not all of the injected fuel made it into the cylinder. To compensate for this we need to inject more fuel than is technically needed for combustion during these transient conditions; this is Acceleration Enrichment.
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