KMS MD35 manual
Version 4.16 28
3.2.4.1.6 Throttle pump effect
When the throttle valve is opened, the engine will draw in
more air and therefore need more fuel to keep the mix
ratio at a constant level. As air is a gaseous substance, it
will reach the inlet valve earlier than the liquid fuel, which
because of its higher inertia needs more time to
accelerate. As a result, there will briefly be a weak mix,
causing the engine to 'hesitate'. The faster the throttle
valve is opened, the greater this effect will be. To
neutralise the effect of fuel having a higher inertia than
air, acceleration enrichment can be applied. This means
that, depending on the throttle valve opening speed, extra
fuel is injected. This prevents the formation of a poor
mixture.
There are two types of acceleration enrichment (these can
be set on/off separately).
We recommend to use „Type 2‟ acceleration enrichment.
Type 1:
The quantity of extra fuel to be injected can be set for the
three engine speed ranges indicated. The duration of
enrichment can be set by entering the number of
crankshaft rotations. The acceleration enrichment will automatically decrease at lower throttle
valve opening speeds. Acceleration enrichment type 1 is always linked to "Engine load 1".
Type 2:
With most engines it is recommended to use only this
acceleration type2. However type 2 can be combined with
type 1 (for some engines useful).
Acceleration enrichment type 2 is always linked to main
engine load.
The initial burst is one pulse that is directly injected when
needed no matter what crank position and will intervene to
avoid a short lean mixture. The sensitivity is linked to
opening speed of the throttle. A low value for sensitivity means that the initial burst won‟t occur
fast, a high throttle opening speed is needed. For a high sensitivity value a lower throttle opening
speed is needed for initial burst enrichment to occur. The amplifier is more or less a factor for the
amount of fuel injected. A higher amplifier results in more enrichment.
Additional enrichment follows after the initial burst. After the initial burst, the mixture briefly can
get lean again. More enrichment is
needed. You can choose how many
rotations the additional enrichment is
needed. The amount of extra fuel will
slowly decrease during these
rotations. Sensitivity and the amplifier
function the same as they do with the
initial burst. The additional
enrichment can be increased by a
percentage for the water
temperature. More enrichment is
needed with a low water
temperature.
The figure on the right gives an
indication of how these two types of
enrichments affect the mixture, when
suddenly the throttle valve is opened.
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