Air/Fuel Ratio.

[Bruce Bowling]

> 
> How do we calculate the amount of fuel needed for a given engine rpm,
> Displacement, etc? Especially if the engine is turbocharged. Can anyone help
> me? or are there any sites that I can find such info?
> 
> 
> thanks and merry christmas
> 
> 

For a speed/density system, one can use the following:

PW=((187.9*CID*(Baro-vp))/(Ncyl*(temp+459.7)*injsiz))*(Map/MapWOT)*Ve

Where:

PW = computed pulse width in milliseconds
CID = cubic inch displacement
Baro = Barometric pressure in Inches Mercury
vp = vapor pressure in Inches Mercury
Ncyl = number of cylinders (integer)
temp = air inlet temperature in F
injsiz = injector flow size in lbs/hr
Map = Manifold Absolute Pressure in any units (like Kpa)
MapWOT = Map reading at wide-open throttle, in any units (consistent w/ Map)
Ve = volumetric efficiency in (percent/100)

The above computes the fuel pulse width needed for one engine cylinder,
with one complete engine "cycle", assuming 14.7 stoch. 

Note that the Map/MapWOT is basically a ratiometric scaling of the
manifold absolute pressure reading.

To add enrichments, like acceleration, warmup, etc, simply
add up the enrichments, and multiply this to the PW in the
form of (1 + SumEnrichments), with the enrichments being in
a form of (PercentEnrichment/100), such that a 100% enrichment
will double the pulse width.

Some simplifications which make the above easier to use:

For a standard correction environment (dry air, 29.92 Inches Hg 
Barometer at sea-level, and 60 degrees F), the above reduces down to:

   PW=((10.8*CID)/(Ncyl*injsiz))*(Map/MapWOT)*Ve

To see the above (generalized) in action, go to:

    http://efi332.eng.ohio-state.edu/bowling/fi.html

To see real detailed mathematics on computation of FI parameters, see:

    http://efi332.eng.ohio-state.edu/grippo/equations.html

- Bruce

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                 Bruce A. Bowling
                 Staff Scientist
   Thomas Jefferson National Accelerator Facility
    12000 Jefferson Ave - Newport News, VA 23606
                 (804) 249-7240
bowling at cebaf.gov  http://devserve.cebaf.gov/~bowling
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