rising rate fuel pressure regulators

[jon hanson]

Michael McBroom wrote 

>Boy, did my equations get fouled up in the word-wrap process.  Let me
>try this again.  For a turbocharged application in which a proportional
>fuel pressure regulator is used, then it seems to me that one cannot use
>the equation:
>
>             P2
> Q2 = Q1 * (----)^0.5
>             P1
>
>to determine flow.  It seems that instead one must use the ratio of the
>differences between fuel rail pressures and intake pressures in order to
>determine new flow rates, since fuel rail pressure increases with
>boost.  The way I see it, the following equation would have to be used:
>
>             P2 - (atmospheric + boost)       
> Q2 = Q1 x (----------------------------)^0.5
>                 (P1 - atmospheric)
>
>where: P1 = fuel rail pressure + atmospheric pressure
>       P2 = P1 + (boost * fpr ratio)
>
>EG #1: using a 1:1 fuel pressure regulator
>
>Given: 1:1 fpr
>       0.8 bar boost
>       Q1 = 300ml/min
>       P1 = 3 bar + 1 bar (rail pressure + atmospheric pressure)
>       P2 = P1 + (boost * fpr ratio)
>
>               ([3 + 1] + [0.8 * 1]) - (1 + 0.8)
>Q2  =  300 x (-----------------------------------)^0.5
>                          ([3 + 1] - 1)
>
>    = 300ml/min = Q1
>
>
>EG #2: using a 2:1 rising rate fuel pressure regulator
>
>Given: all of the above, but with a 2:1 rrfpr
>
>               ([3 + 1] + [0.8 * 2]) - (1 + 0.8)
> Q2 = 300 x (------------------------------------)^0.5
>                         ([3 + 1] - 1)
>
>    = 338ml/min
>
>
>This still seems to be the right approach to me.  If I've committed an
>egregious error anywhere, though, please let me know.
>
>-- 
>Best,
>
>Michael McBroom

Here's my 2c worth
I installed an fse rising rate fpr to overcome a problem of running my
injectors at too high a duty cycle at highest revs and WOT.
the adds for fse say fp increases 1.7 parts for every part of air
I took this to mean it is a 1.7 : 1 fp reg(simpler if they just said so)
The Engine is NON TURBO but the same argument applies
I set fuel pressure at idle to 2.7 bar (at which the nippondenso injectors
deliver 20.55 lbs/hr) my MAP reading at idle is 0.25 bar.
MAP at WOT is 1 bar so there is an increase of pressure 0f 0.75 bar
in opening the throttle from idle to WOT.
if it was a 1:1 reg then the fp would have risen by 0.75 bar
to maintain a const 2.7 bar accross the injectors.Since it is a 1.7 : 1 fpr
the EXTRA increase in fp is (0.7 * 0.75)= 0.525 bar
so P new = 2.7 + 0.525 = 3.225 bar
   P old = 2.7

new flow rate at WOT = 20.55 (old flow rate) * sqrt(3.225/2.7)
                     = 22.46 lbs/hr

the flow rate at idle remains 20.55 lbs/hr
  
This is the same end result as Michaels formula
so I agree with him.
I'm a begginer so if this is all wrong I would appreciate being
pointed in the right direction

Regards Jon Hanson.