Air flow measurement

[Todd Knighton]

> Through all the discussions regarding air flow measurement, I think we have established that using a MAF sensor
> as the main input generally results in some error due to air flow reversion.  I have two questions:
> 
> 1)  What is the best way to quantify the error on an actual engine?

	We typically just let the mass air flow sensor think whatever it wants
and write in a trim map, just like you would a pressure sensing system
to compensate for the volumetric efficiency curve.  As long as the
condition is repeatable, who really cares if the computer thinks it's
getting 10% more flow at a given rpm because of reversion effects, as
long as you can trim the fuel quantity repeatably to a good output fuel
number.  If you're trying to use a maf for high resolution data
aquisition however, you'll have to put a very large plenum between the
engine and the maf to dampen out any reversion or pulsations and read
only incoming airflow.


Todd Knighton
Protomotive Engineering