[Diy_efi] Re: CIS EFI via Fuel Pump PWM

[Bernd Felsche]

Kenny Bauman tapped away at the keyboard with:

> Not sure I understand the 100:1 range needed of the
> pump.
> 
> Perhaps you can clarify?

Idle fuel requirements vs. peak fuel at max revs at WOT.

> The CIS injectors only see a range of 45 to 60 psi
> during operation. I think some of the dynamic range is
> handled by the PWM effect of the injectors themselves.

PWM effect? The injectors are either on or off, injecting
"continuously" when sufficient pressure is available to open the
pintle valve.

> Remember they have a spring loaded valve that
> constantly closes and opens. Sort of a mechanical PWM
> that changes with pressure. Which of course changes
> flow. But I really don't have that good of an
> understanding of it all.

I wasn't aware of that.  The valve pin vibrates to aid atomization.
Maybe Bosch literature is over-simplifying their descriptions.

> I think part of the original intent has been lost over
> the posts. The orginal idea was a dead nuts simple
> system that did away with the fuel regulator and
> return line.

Another spanner in the works is that the Bosch roller cell fuel pump
is cooled by the flow of fuel. Reduce fuel flow and you reduce
cooling. At idle, you'd only get perhaps 5% of the maximum fuel flow
through the pump - if you're prepared to idle fast. Most of the time
(if you're not racing), 10% to 20% would be typical.

The roller-cell pump is not positive-displacement - it requires a
minimum speed of operation to provide pressure. (That speed is
usually at around 8V supply voltage for a new pump.)

Another type of pump could do the job.

-- 
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