Accel enrichment

[Raymond C Drouillard]

On Mon, 23 Mar 1998 16:27:42 -0600 Joe Boucher <BoucherJC at lmtas.lmco.com>
writes:
>Okay you scurvy dogs, why don't you sparkies and software geeks  move
>aside and let this M.E. type have some elbow room and REALLY make a fool
>of himself and try on a HUGE cone shaped hat.

<snip>

>Let's review.  Steady state at 20% throttle equals 19 inches of vacuum.
>40% throttle equals 16 inches.  When the throttle snaps from 20% to 40%,
>the needle will drop to as low as 10 inches.  The pressure in the
>manifold goes beyond the upcoming steady state value, then sinks back to
>the new value.  That means there are more molecules bouncing around in
>the manifold than at steady state.  I can't for the life of me visualize
>why.

When you open the throttle, a whole bunch of air rushes in.  As the
pressure equalizes, the air is still moving.  The inertia of the fast
moving column of air "rams" more air in.  This effect is used to increase
low-end torque in an engine.  An engine designed for low-end torque will
have narrow passages in the intanke and exhaust manifolds.  This
increases the velocity of the gas.

<snip>

>So what's my point?  Well, the fuel may be flashing out of solution as a
>previous poster suggested (I thought the amount of liquid suspension
went
>UP when pressure increases, that's why it rains when the temperature and
>barometric pressure go down) but, for some mysterious reason, there is
>also more air in the manifold and therefore to keep the proper recipe,
>more fuel is required for acceleration.

The fuel comes out of solution because the pressure has gone above the
vapor pressure of the fuel.

If you put a dish of water into a vacuum, it will boil.  The vapor
pressure is higher than the ambient pressure.  Gasoline acts the same
way.

>Joe Boucher
>'70 RS/SS Camaro  '81 TBI Suburban


Ray Drouillard, BSEE
(who was forced to take physics and thermodynamics in school, and is
currently working at earning a conical hat)

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