Accel enrichment

[Joe Boucher]

Before we spin off the original request by trying to out thermo each
other (obviously I've forgotten too much to win) and look at what was
asked.

Tony Bryant wrote:

> Why is accel enirchment (== throttle pump) needed?

I say more air is being used.  I can't prove it scientifically.

> I'm talking about the momentary increase in required injector
> duration when the throttle is quickly opened, as opposed to constant
> running at WOT at that RPM.
>
> For example a transition between from 15" vac to 0" (WOT) at say 2000
> RPM.
>
> 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.
>
> What is going on in terms of MAP, air flow velocity, pressure,
> fuel vaporisation and VE?

MAP; I explained my observations.Air Flow Velocity; My observations lead
me to think the air flow increases beyond the steady state for that
throttle setting.  Pressure; Above what is needed at that steady state
throttle setting.
Fuel vaporisation; because the pressure rises, fuel may flash out of
suspension adding to the requirement of more fuel.  However, Smokey
Whatsisname put a plexiglass window in a manifold and observed rivers of
fuel running down the manifold runners in one of his NASCAR engines at
full throttle.  So, we talk about vaporization, but is what really
happens?  Look down a GM TBI while it's idling.  You can see the fuel
running off the throttle blades.  I'm sure it flashes to vapor after it
passes into the low pressure region on the other side of the TBI.
VE; at wide open throttle, the VE of an engine depends on the matching of
the camshaft, intake, and exhaust designs and is RPM dependent.  Nothing
new there.  Peter added the observation that the flow rate is a sine
function for a butterfly throttle system.

>
>
> What algorithm are in use, and what do they depend on?

I haven't figured that out, yet.

>
>
> Any help greatly appreciated.

Have we helped you, any?

My suggestion is to mount a vacuum gage on a car and watch it's behavior
under various throttle postitions and accelerations.

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