Accel enrichment

[Gary Derian]

During periods of high intake vacuum, the fuel in an intake manifold,
especially wet flow types, evaporates easily.  There is little wet fuel
clinging to the manifold walls.  When the throttle is opened, the fuel in
the air stream, quickly condenses onto the manifold walls creating a very
lean mixture.  The accelerator pump makes up for this.  Manifold design and
temperature have a large effect on the amount of enrichment needed.  When
the throttle is snapped shut, the opposite happens and a rich slug of fuel
goes through the engine.  This is why carbureted and TBI injection has a
hard time meeting emissions when used with stick shift transmissions.  At
every shift there is a spike of HC.  Port injection (dry flow) needs very
little accel enrichment compared to wet flow systems.

Gary Derian <gderian at cybergate.net>


Tony Bryant <Tony.Bryant at psc.fp.co.nz> wrote


>Why is accel enirchment (== throttle pump) needed?
<snip>
>I'm trying to optimize this part of my algorithm, and I need to
>have some sort of understanding of what I'm trying to fix.
>