Air Flow Measurement

[Anthony Tsakiris]

>>(FYI - Air flow could be calculated from a differential pressure manometer
by measuring air pressure in an appropriately sized (perhaps 4 inch dia.)
venturi located before the throttle plates.  Air velocity through the
venturi throat is related to the difference in pressure between the venturi
throat and the pressure before the venturi.  Air velocity is thus used
(along with air temperature) to determine total air mass flowing into the
intake system.)

If you knew velocity and area, you could calculate
volumetric flow rate.  This assumes that average 
velocity measure you have adequate represents the
real velocity profile over the area.  You still to 
know density to determine mass flow rate.

>If you know BAP and MAP, you know delta-P across opening -- granted,
the opening size varies with throttle position, but you've got TPS
for that -- seems that air flow could be rather accurately determined
without much hassle?????

OK, now you've added barometric pressure (and you had
temperature above), so you can figure out ambient air 
density.  And you're transforming throttle angle
to area, so presumably you can get mass flow rate.  
(Assumption: flow coefficient of throttle (or orifice for
that matter) is known.)

But is it any less of a hassle than using a MAF sensor?
I don't see a huge advantage of one system over the other.

Anthony Tsakiris



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