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Acceleration Enrichment

EFI Tuning Fundamentals

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I have some doubts regarding Acceleration Enrichment. In the video it explains that, the fuel being supplied behind valve, get evaporated due to the high temperature in the cylinder. the volume of fuel deposited behind the valve is directly proportional to the manifold pressure. At higher manifold pressure more fuel has to be injected to compensate the evaporation process. If this is what I have understood from the video. then my question is.

Why do we need to compensate the evaporation process, even the fuel in gaseous form gets burnt , right?

Also when there is rapid change in the throttle body, the manifold pressure also increases rapidly. Hence more evaporation occurs. why do I need to add more fuel , if the evaporated fuel goes inside at gets burnt. Am I not making the A/F ratio more richer my adding more fuel through acceleration enrichment option.

Please make this concept clear to me. If I have understood it wrongly. :-)

Actually, less evaporation occurs, which is why you need to add fuel, so more will be available for evaporation.

The requirement for accel enrichment is all down to the size of the fuel puddle on the port wall. Under steady state conditions the fuel puddle is being topped up at the same rate as the fuel is evaporating off or in some way entering the cylinder and combusting so all the fuel being delivered by the injector essentially gets combusted. The size of the fuel puddle varies depending on air speed and manifold pressure and under transient conditions we can see a lean period as the puddle size is being increased (so some portion of the injected fuel is momentarily increasing the fuel puddle size and is not entering the cylinder. Once steady state is achieved under the new operating conditions we're back to all the fuel that's injected being combusted. The opposite occurs when we tip out of the throttle as the fuel puddle size decreases so we end up with more fuel entering the cylinder than the injector is supplying.

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