Alpha-N vs. Speed Density?

[Bernd Felsche]

steve ravet tapped away at the keyboard with:

> Alpha-N uses two inputs:  Throttle position (alpha) and RPM (n).  These
> two numbers are used to estimate airflow, then fuel is injected based on
> that airflow.

> speed-density uses MAP (manifold absolute pressure/density) and RPM
> (speed) as its main inputs, but usually incorporates other factors like
> air temp.  From RPM you know the volume of air going thru the engine,
> and from MAP you know the pressue, you can measure or guess at
> temperature, and from all that you can calculate the mass of air going
> into the engine.  Then inject fuel based on that.  In practice the
> calculations are done ahead of time and put into a table that has RPM on
> one axis, MAP on the other, and VE is the value returned.

> alpha-n is the most basic type of EFI, AFAIK only used on engines where
> you can't really measure MAP (throttle/cylinder, lots of overlap, etc.).

Or on cost-sensitive systems such as Bosch Mono-Motronic/Jetronic.
These tend to use EGO feedback for mixture "calibration", typically
on small engines (under 2 litres).

-- 
Bernd Felsche - Innovative Reckoning
Perth, Western Australia
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