pintle vs. disc injector types

[Jeffrey Engel]

I don't think outside pressure would affect it.  The systems I am 
aware of reference the FPR to the intake manifold, so:

Fuel pressure is:              P1 + Constant (about 30-41 psi) and P1 
                                                       is the pressure inside the intake

the pressure at the end of the injector is: P1 (minus a bit due to 
                                                                    air flow resistance.
                                                              Maybe a max of 1-3inHg)

Keeping a constant pressure differential across the injector allows the
computer to assume a fairly constant mass/time(open).  It could work 
the other way as well, but it would take a lot more tuning.

============================================
> Date:          Thu, 21 Aug 1997 17:57:07 -0700
> From:          Michael McBroom <bodhi at earthlink.net>
> Organization:  http://mcbrooms.com
> To:            diy_efi at coulomb.eng.ohio-state.edu
> Subject:       Re: pintle vs. disc injector types
> Reply-to:      diy_efi at coulomb.eng.ohio-state.edu

> A70Duster at aol.com wrote:
> > 
> > The pintle type is pretty linear between 10% and about 80%.  At least with
> > the pintle type, the fuel flow rate changes as the square root of the ratio
> > of the different pressures.
> > 
> >                                Q2 = Q1 (P2/P1)^0.5
> 
> A follow-up to this, if I might.  In the turbocharged applications I'm
> familiar with, a 1:1 fuel pressure regulator is used, which increases
> fuel rail pressure in direct proportion to the increase in boost
> pressure.  What I'm wondering is, if the presssure downstream of the
> injector has increased by the same amount as the pressure upstream of
> the injector, won't this affect the predicted outcome?  And if it will,
> shouldn't a ratio of delta-Ps be used instead, where delta-P1 = [(fuel
> rail pressure + atmospheric) - (atmospheric)] and delta-P2 = ([(fuel
> rail pressure + atmospheric) + (boost * fpr ratio)] - [atmospheric +
> boost])?  At a 1:1 fpr ratio, P2/P1 will equal 1, thus Q2 = Q1.  But at
> a different fpr, which is a popular mod some folks use to increase fuel
> flow, Q2 should increase, but only by the differential amount.  Right?
> 
> EG #1:
> 
> 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)
> 
>             P2 - (1 + 0.8)                   ([3 + 1] + [0.8 * 1]) - (1
> + 0.8)
> Q2 = Q1 x (----------------)^0.5  =  300 x
> (-----------------------------------)^0.5 = 300ml/min = Q1
>                (P1 - 1)                               ([3 + 1] - 1)
> 
> EG #2:
> 
> Given: all of the above, but with a 2:1 rising rate fuel pressure
> regulator
> 
>                ([3 + 1] + [0.8 * 2]) - (1 + 0.8)
>  Q2 = 300 x (------------------------------------)^0.5 = 338ml/min
>                          ([3 + 1] - 1)
> 
> -- 
> Best,
> 
> Michael McBroom
> 
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> 
je
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